GLOSSARY

A

5' VNTR.: A specific variation outside the insulin gene that is implicated in NIDDM and IDDM susceptibility.
AADC INHIBITORS.: Drugs that block the amino acid decarboxylase; one type of enzyme that breaks down dopamine. Also called DC inhibitors, they include carbidopa and benserazide.
ABDOMINAL HERNIA.: Bulging of an organ or tissue through the muscle of the stomach wall.
ABDUCENS NERVE.: Cranial nerve VI; the nerve that extends from the midbrain to the lateral rectus muscle of the eye and controls movement of the eye toward the ear (abduction).
ABDUCTION.: Turning away from the body.
ABSCESS.: A localized collection of pus or infection that is walled off from the rest of the body.
ABSENCE SEIZURE.: A brief seizure with an accompanying loss of awareness or alertness.
ACAMPROSATE.: An anti-craving medication used in Europe to reduce the craving for alcohol. It is presently undergoing tests for approval in the United States.
ACANTHOCYTOSIS.: The presence of acanthocytes in the blood. Acanthocytes are red blood cells that have the appearance of thorns on their outer surface.
ACANTHOSIS NIGRICANS.: A skin condition characterized by darkly pigmented areas of velvety wart-like growths. Acanthosis nigricans usually affects the skin of the armpits, neck, and groin.
ACCOMMODATION.: The ability of the lens to change its focus from distant to near objects. It is achieved through the action of the ciliary muscles that change the shape of the lens.
ACETYLCHOLINE.: A neurotransmitter (chemical messenger) used to certain nerve cells to send messages to adjacent cells.
ACETYLCHOLINESTERASE (ACHE).: An enzyme found in nerve tissue.
ACHROMATOPSIA.: The inability to distinguish any colors.
ACID MALTASE.: The enzyme that regulates the amount of glycogen stored in muscle cells. When too much glycogen is present, acid maltase is released to break it down into waste products.
ACIDOSIS.: A condition of decreased alkalinity resulting from abnormally high acid levels (low pH) in the blood and tissues. Usually indicated by sickly sweet breath, headaches, nausea, vomiting, and visual impairments.
ACONDROPLASIA.: An autosomal dominant form of dwarfism caused by a defect in the formation of cartilage at the ends of long bones. Affected individuals typically have short limbs, a large head with a prominent forehead and flattened profile, and a normal-sized trunk.
ACQUIRED ANGIONEUROTICEDEMA.: Abbreviated AANE, or AAE, this is a non-hereditary form of angio edema that generally begins to show symptoms in, or after, the fourth decade of life.
ACQUIRED IMMUNITY.: Also called "specific immunity," refers to immune reaction mediated by B-cells and/or T-cells. Includes humoral and cellular immunity.
ACROCENTRIC.: A chromosome with the centromere positioned at the top end.
ACROCEPHALOPOLYSYNDACTYLY SYNDROMES.: A collection of genetic disorders characterized by cone shaped abnormality of the skull and partial fusing of adjacent fingers or toes.
ACROCEPHALY.: An abnormal cone shape of the head.

ACROMELIC.: The anatomical term used to denote the end of a limb (arm or leg). In the context of Robinow syndrome, it refers to bones of the hands and feet.
ACROOSTEOLYSIS.: Loss of bone tissue at the ends of the fingers and/or toes.
ACROPARESTHESIAS.: Painful burning sensation in hands and feet.
ACTION POTENTIAL.: The wave-like change in the electrical properties of a cell membrane, resulting from the difference in electrical charge between the inside and outside of the membrane. The action potential acts as a signal for certain activities and processes in the body.
ACUPUNCTURE.: An alternative health procedure based on ancient Chinese methods, involving insertion of thin needles at specific pressure points in the body.
ACUTE PHASE REACTANTS.: Blood proteins whose concentrations increase or decrease in reaction to the inflammation process.
ACUTE PHASE.: The initial phase of LHON where visual blurring begins in both eyes, and central vision is lost.
ADDUCTED THUMBS.: Thumbs clasped across the palm.
ADDUCTION.: Movement toward the body. In Duane retraction syndrome, turning the eye inward toward the nose.
ADENOCARCINOMA.: A type of cancer which is in a gland-like form.
ADENOMATOUS.: Derived from glandular structures
ADRENAL.: A pair of glands located on top of the kidneys that secrete substances or hormones, like steroids and adrenaline, which regulate various functions, such as water balance and stress response.
ADRENAL GLAND.: A triangle-shaped endocrine gland, located above each kidney, that synthesizes aldosterone, cortisol, and testosterone from cholesterol. The adrenal glands are responsible for salt and water levels in the body, as well as for protein, fat, and carbohydrate metabolism.
ADRENAL INSUFFICIENCY.: Problems with the adrenal glands that can be life threatening if not treated. Symptoms include sluggishness, weakness, weight loss, vomiting, darkening of the skin and mental changes.
ADRENOCORTICOTROPIN (CORTICOTROPHIN).: A hormone that acts on cells of the adrenal cortex, causing them to produce male sex hormones and hormones that control water and mineral balance in the body.
ADVANCED BONE AGE.: The bones, on x-ray, appear to be those of an older individual.
ADYSPLASIA.: A term referring to the combination of renal agenesis (complete absence of one or both kidneys) and renal dysplasia (developmental anomaly of the kidney).
AFFECTIVE FLATTENING.: A loss or lack of emotional expressiveness. It is sometimes called blunted or restricted affect.
AFLATOXIN.: A substance produced by molds that grow on rice and peanuts. Exposure to aflatoxin is thought to explain the high rates of primary liver cancer in Africa and parts of Asia.
AGE-ASSOCIATED MEMORY IMPAIRMENT (AAMI).: A condition in which an older person suffers some memory loss and takes longer to learn new information. AAMI is distinguished from dementia in that it is not progressive and does not represent a serious decline from the person's previous level of functioning.
AGENESIS.: Failure of an organ, tissue or cell to develop or grow.
AGENESIS OF THE CORPUS CALLOSUM.: Failure of the corpus callosum to form and develop. The corpus callosum is the band of nerve fibers located between the two sides, or hemispheres, of the brain.
AGNOSIA.: Loss of the ability to recognize objects by use of the physical senses.
AGYRI.: A lack of convolutions (gyri) or normal folds in the brain tissue.
AKATHISIA.: Agitated or restless movement, usually affecting the legs and accompanied by a sense of discomfort. It is a common side effect of neuroleptic medications.
AKINESIA.: A loss of the ability to move; freezing in place.
ALKALINE.: Having a basic pH; not acidic.
ALKALINIZATION.: The process of making a solution more basic, rather than more acidic, by raising the pH.
ALLELE.: One of two or more alternate forms of a gene.
ALLELIC.: Related to the same gene.
ALLELIC VARIANTS.: A disease is said to have allelic variants when different mutations in the same allele result in identical, or nearly identical, symptoms. An allele is the combined locations of a gene on the two paired chromosomes that contain this gene.

ALLERGEN.: A substance or organism foreign to the body; allergens stimulate the immune system to produce antibodies.
ALLERGIC RHINITIS.: Hay fever.
ALLERGY.: Condition in which immune system is hypersensitive to contact with allergens; an abnormal response by the immune system to contact with an allergen; condition in which contact with allergen produces symptoms such as inflammation of tissues and production of excess mucus in respiratory system.
ALLOSTERIC ACTIVATOR SITE.: Site at which an enzyme is regulated separate from its site of catalytic enzymatic activity.
ALOPECIA AREATA.: A nonscarring hair loss syndrome characterized by smooth round or oval hairless areas on the scalp.
ALOPECIA.: Loss of hair or baldness.
ALPHA-FETOPROTEIN (AFP).: A chemical substance produced by the fetus and found in the fetal circulation. AFP is also found in abnormally high concentrations in most patients with primary liver cancer.
ALPHA-L-IDURONIDASE..: An enzyme that breaks down dermatan sulfate and heparan sulfate. People with Hurler syndrome do not make enough of this enzyme.
ALPHA-THALASSEMIA.: Autosomal recessive disorder where no functional hemoglobin is produced. Leads to severe untreatable anemia.
ALTERATION.: Change or mutation in a gene, specifically in the DNA that codes for the gene.
ALTERNATE COMPLEMENT PATHWAY.: A cascade of enzymatic reactions that produce antibacterial proteins. This pathway helps to ward off infections.
ALZHEIMER DISEASE.: A neurodegenerative disease marked by the loss of cognitive ability, generally over a period of 10–15 years, associated with the development of abnormal tissues and protein deposits in the brain.
AMASTIA.: A birth defect involving absent breast(s).
AMBIGUOUS.: Unclear or open to more than one interpretation.
AMELOGENESIS IMPERFECTA.: A hereditary dental defect characterized by discoloration of the teeth.
AMINO ACID.: Organic compounds that form the building blocks of protein. There are 20 types of amino acids (eight are "essential amino acids" which the body cannot make and must therefore be obtained from food).
AMNIOCENTESIS.: A procedure performed between 16 and 18 weeks of pregnancy in which a needle is inserted through a woman's abdomen into the uterus to draw out a small sample of the amniotic fluid from around the fetus; either the fluid itself or cells from the fluid can be used for a variety of tests to obtain information about genetic disorders and other medical conditions in the fetus.
AMNION.: The thin, protective sac that suspends the fetus in a protective amniotic fluid.
AMNION.: Thin, tough innermost layer of the amniotic sac.
AMNIOTIC FLUID.: The liquid in the amniotic sac that cushions the fetus and regulates temperature in the placental environment. Amniotic fluid also contains fetal cells.
AMNIOTIC SAC.: The membranous sac that contains the fetus and the amniotic fluid during pregnancy.
AMNIOTIC SAMPLE.: Sample of amniotic fluid, the protective fluid surrounding a fetus in the womb.
AMPLIFICATION.: A process by which something is made larger. In clotting, only a very few chemicals are released by the initial injury; they result in a cascade of chemical reactions which produces increasingly larger quantities of different chemicals, resulting in an appropriately-sized, strong fibrin clot.
AMPUTATION.: Surgical removal of any portion of the body.
AMYLASE.: A digestive enzyme found in saliva or pancreatic fluid that breaks down starch and sugars.
AMYLOID.: A waxy translucent substance composed mostly of protein, that forms plaques (abnormal deposits) in the brain.
AMYLOIDOSIS.: Accumulation of amyloid deposits in various organs and tissues in the body such that normal functioning of an organ is compromised.
AMYOPLASIA.: The mildest form of arthrogryposis muliplex congenita, characterized by sporadic and recurrent contractures of the wrists, elbows, and knees; club feet, and an abnormal internal rotation of the shoulders.
AMYOTROPHIC LATERAL SCLEROSIS (ALS).: A neurodegenerative disease that is caused by degeneration of the motor fibers and neurons in the brain, brainstem, and spinal cord, leading to stiffness, weak muscles, and respiratory failure. Also called Lou Gehrig's disease.
ANAGEN.: The growth phase of the human hair growth cycle.
ANALYTE.: A chemical substance such as an enzyme, hormone, or protein.

ANDROGENS.: A group of steroid hormones that stimulate the development of male sex organs and male secondary sexual characteristics.
ANEMIA.: A condition in which there is an abnormally low number of red blood cells in the bloodstream. It may be due to loss of blood, an increase in red blood cell destruction, or a decrease in red blood cell production. Major symptoms are paleness, shortness of breath, unusually fast or strong heart beats, and tiredness.
ANESTHESIA.: Lack of normal sensation (especially to pain) brought on by medications just prior to surgery or other medical procedures.
ANESTHETIC.: Drug used to temporarily cause loss of sensation in an area of the body. An anesthetic may either be general, associated with a loss of consciousness, or local, affecting one area only without loss of consciousness. Anesthetics are administered either via inhalation or needle injection.
ANEUPLOIDY.: Having too many or too few copies of a specific chromosome; the most common forms are trisomy (three) and monosomy (one); two copies of a chromosome is normal.
ANEURYSM.: Widening of an artery, which could eventually bleed.
ANGELMAN SYNDROME.: A syndrome caused by a deletion in the maternally inherited chromosome 15 or uniparental disomy of the paternal chromsome 15.
ANGIOGRAPHY.: Radiographic examination of blood vessels after injection with a radiopaque contrast substance or dye.
ANGIOID STREAKS.: Gray, orange, or red wavy branching lines in Bruch's membrane.
ANGIOKERATOMA.: Skin rash comprised of red bumps. Rash most commonly occurs between the belly button and the knees.
ANGIOMA.: A benign tumor composed of blood vessels or lymph vessels.
ANGIONEUROTIC EDEMA.: Recurrent episodes of swelling of the tissues of the body caused by an overactive immune system. This is aslo called angioedema.
ANGIOTENSINOGEN.: A plasma globulin (protein) formed in the liver and directly involved in the regulation of blood pressure.
ANKYLOSIS.: Immobility of a joint due to the formation of new bone at the site of inflammation.
ANOMALOUS VENOUS RETURN.: Normally, the veins that bring blood containing oxygen from the lungs to the heart (called pulmonary veins) are connected to the left atrium. In this situation, the pulmonary veins are connected to the right atrium.
ANOMALOUS.: Irregular or different from normal.
ANOMALY.: Generally, something that is different from what is normal or expected. More specifically in medicine, a malformation or abnormality in any part of the body.
ANOPTHALMIA.: A medical condition in which one eye is missing.
ANOTIA.: Absence of an ear.
ANTERIOR FONTANELLE.: The soft-spot on the skull of an infant that is located in the center of the head just behind the hairline.
ANTERIOR HORN CELLS.: Subset of motor neurons within the spinal cord.
ANTI-ANDROGEN DRUGS.: Drugs that block the activity of the male hormone.
ANTIBIOTICS.: A group of medications that kill or slow the growth of bacteria.
ANTIBODY.: A special protein made by the body's immune system as a defense against foreign material (bacteria, viruses, etc.) that enters the body. It is uniquely designed to attack and neutralize the specific antigen that triggered the immune response.
ANTICIPATION.: The apparent tendency of certain diseases to appear at earlier ages and with increasing severity in successive generations.
ANTICOAGULANT.: Drugs used to prevent blood clots.
ANTIDIURETIC HORMONE (VASOPRESSIN).: A hormone that acts on the kidneys to regulate water balance.
ANTIGEN.: A substance or organism that is foreign to the body and stimulates a response from the immune system.
ANTIGEN PRESENTING CELL.: Cells that are able to present foreign antigen in conjunction with MHC proteins to the immune system.
ANUS.: The opening at the end of the intestine that carries waste out of the body
AORTA.: The main artery located above the heart which pumps oxygenated blood out into the body. Many congenital heart defects affect the aorta.
AORTIC REGURGITATION.: A condition in which the aortic valve does not close tightly, allowing blood to flow backwards from the aorta into the heart.

AORTIC ROOT.: The location where the aorta (main heart blood vessel) inserts in the heart. Enlargement of the aortic root can cause it to rupture.
AORTIC STENOSIS.: A condition in which the aortic valve does not open properly, making it difficult for blood to leave the heart.
APHASIA.: The loss of the ability to speak or to understand written or spoken language. A person who cannot speak or understand language is said to be aphasic.
APLASIA.: Defective development resulting in absence of all or part of an organ or tissue.
APLASTIC ANEMIA.: A form of anemia characterized by a greatly decreased formation of red and white blood cells as a result of abnormal bone marrow.
APNEA.: An irregular breathing pattern characterized by abnormally long periods of the complete cessation of breathing.
APOENZYME.: An enzyme that cannot function without assistance from other chemicals called cofactors.
APOPTOSIS.: The normally programmed cell death process in which cells die in order to be replaced with new cells.
APPENDECTOMY.: The procedure to surgically remove an appendix.
APPENDICITIS.: Inflammation of the appendix.
APPENDIX.: A portion of intestine attached to the cecum.
APRAXIA.: Impairment of the ability to make purposeful movements, but not paralysis or loss of sensation.
AQUEOUS HUMOR.: A fluid produced by the ciliary body and contained within the front chamber of the eye.
ARACHNODACTYLY.: A condition characterized by abnormally long and slender fingers and toes.
ARNOLD-CHIARI MALFORMATION.: A congenital anomaly in which parts of the brain protrude through the opening in the base of the skull into the spinal column.
ARRHYTHMIA.: Abnormal heart rhythm, examples are a slow, fast, or irregular heart rate.
ARTERIAL.: Term used to describe an artery or the entire system of arteries.
ARTERIOLE.: The smallest type of artery.
ARTERIOPATHY.: Damage to blood vessels.
ARTERIOSCLEROSIS.: Hardening of the arteries that often results in decreased ability of blood to flow smoothly.
ARTERIOVENOUS MALFORMATION (AVM).: Abnormal, direct connection between the arteries and veins (blood vessels). Can range from very small to large in size. Bleeding or an aneurysm may result.
ARTERY.: A blood vessel that carries blood away from the heart to peripheral tissues.
ARTHROCHALASIA.: Excessive loosness of the joints.
ARTHROGRYPOSIS.: Abnormal joint contracture.
ASPERGER SYNDROME.: A term used to describe high-functioning individuals with autism. These individuals usually have normal IQ and some language skills.
ASPHYXIA.: Lack of oxygen. In the case of cerebral palsy, lack of oxygen to the brain.
ASPIRATION PNEUMONIA.: Lung infection due to food or liquids accidentally getting into lungs.
ASPIRATION.: Inhalation of food or saliva.
ASPLENIA.: The absence of the spleen in the body.
ASSOCIATION.: A non-random occurrence in two or more individuals of the same group of anomalies that are not otherwise known to be a sequence or syndrome.
ASTIGMATISM.: A cause of poor eyesight, usually due to an error in the refraction of light within the eye.
ASTROCYTOMA.: Tumor of the central nervous system derived from astrocytes
ASYMMETRIC SEPTAL HYPERTROPHY.: A condition in which the septum (the wall that separates the atria of the heart) is abnormally excessively thickened. In microscopic examination, normal alignment of muscle cells is absent (myocardial disarray).
ASYMMETRY.: Without symmetry, as when a disease, condition, or symptom is not manifested equally on both sides of the body or body part.
ASYMPTOMATIC.: Without symptoms.
ASYMPTOMATIC CARRIER.: A person who carries a recessive trait but does not show any characteristics of the trait.
ATAXIA.: A condition marked by impaired muscular coordination, most frequently resulting from disorders in the brain or spinal cord.
ATHEROSCLEROSIS.: Hardening of the arteries caused by cholesterol and fat deposits. Increases risk of heart disease, stroke, and other complications.
ATHETOSIS.: A condition marked by slow, writhing, involuntary muscle movements.
ATOPIC.: A condition or disease that is the result of an allergic reaction.

ATOPIC ASTHMA.: Asthma caused by an allergic reaction; atopic asthma tends to have a strong inherited component (tends to run in families).
ATOPIC RHINITIS.: Also referred to as "hay fever"; symptoms of rhinitis caused by an allergic response to the presence of an allergen (such as tree or grass pollen).
ATP.: Adenosine triphosphate. The chemical used by the cells of the body for energy.
ATRESIA.: An abnormal condition in which a structure that should be hollow is fused shut.
ATRIA/ATRIUM.: The upper chamber of the heart. Typically, there are two atrias, one on the right side and one on the left side of the heart.
ATRIAL SEPTAL DEFECT (ASD).: An abnormal opening between the two upper chambers (atria) of the heart.
ATROPHIC DERMATOSIS.: Wasting away of the skin.
ATROPHIC PHASE.: The final phase of LHON where cells in the optic disc and optic nerve have atrophied, resulting in legal blindness. Peripheral vision remains.
ATROPHY.: The wasting away or decrease in size of a cell, tissue, organ, or part of the body caused by lack of nourishment, inactivity, or loss of nerve supply.
ATTENTION DEFICIT HYPERACTIVITY DISORDER (ADHD).: A condition in which a person (usually a child) has an unusually high activity level and a short attention span. People with the disorder may act impulsively and may have learning and behavioral problems.
ATYPIA.: Lacking uniformity.
ATYPICAL PERSONALITY DEVELOPMENT.: Another term for pervasive development disorder (PDD-NOS). Other synonyms for this diagnostic category are atypical autism and atypical PDD.
AUDIOGRAM.: A graph of hearing level versus frequency. An audiologist plots the hearing loss of a patient on this graph to help to determine the type of hearing loss and possible treatments.
AUDITORY NERVE.: The nerve responsible for transmitting electrical impulses created within the ear in response to sounds to the brain.
AURICULO.: Related to the ear.
AUTISM.: A developmental disability that appears early in life, in which normal brain development is disrupted and social and communication skills are retarded, sometimes severely.
AUTISTIC PSYCHOPATHY.: Hans Asperger's original name for Asperger syndrome, which is still used occasionally as a synonym for the disorder.
AUTISTIC SPECTRUM DISORDERS.: Another term for the pervasive developmental disorders.
AUTOANTIBODY.: An antibody that reacts against part of the self.
AUTOIMMUNE.: Referring to an immune reaction erroneously directed toward 'self' tissues.
AUTOIMMUNE DISORDER.: One of a group of disorders, like rheumatoid arthritis and systemic lupus erythematosus, in which the immune system is overactive and has lost the ability to distinguish between self and non-self. The body's immune cells turn on the body, attacking various tissues and organs.
AUTONOMIC NERVOUS SYSTEM.: The part of the nervous system that regulates heart muscle, smooth muscle, and glands.
AUTOSOMAL.: Relating to any chromosome besides the X and Y sex chromosomes. Human cells contain 22 pairs of autosomes and one pair of sex chromosomes.
AUTOSOMAL DISEASE.: A disease caused by a gene located on an autosomal chromosome.
AUTOSOMAL DOMINANT.: A pattern of inheritance in which only one of the two copies of an autosomal gene must be abnormal for a genetic condition or disease to occur. An autosomal gene is a gene that is located on one of the autosomes or non-sex chromosomes. A person with an autosomal dominant disorder has a 50% chance of passing it to each of his or her offspring.
AUTOSOMAL RECESSIVE.: A pattern of inheritance in which both copies of an autosomal gene must be abnormal for a genetic condition or disease to occur. An autosomal gene is a gene that is located on one of the autosomes or non-sex chromosomes. When both parents have one abnormal copy of the same gene, they have a 25% chance with each pregnancy that their offspring will have the disorder.
AXON.: Skinny, wire-like extension of nerve cells.

B

B CELL.: Specialized type of white blood cell that is capable of secreting infection-fighting antibodies.
BALANCED CHROMOSOME TRANSLOCATION.: A rearrangement of the chromosomes in which two chromosomes have broken and exchanged pieces without the loss of genetic material.
BAND.: A specific region of a chromosome that is identified by its characteristic staining pattern and location within a chromosome, as seen in a karyotype. A band is either part of the short arm (p arm) or the long arm (q arm) of a chromosome and is further defined by a numeric location, such as chromosome band 11q24.1.

BARIUM ENEMA X RAY.: A procedure that involves the administration of barium into the intestines by a tube inserted into the rectum. Barium is a chalky substance that enhances the visualization of the gastrointestinal tract on x ray.
BARIUM.: A chemical put into a solution and swallowed to help with outlining the gastrointestinal system during an x-ray study.
BASAL CELL CARCINOMA.: A cancer originating from skin.
BASAL GANGLIA.: A section of the brain responsible for smooth muscular movement.
BASE PAIRS.: Building blocks of DNA, the chemical that genes are made of.
BASEMENT MEMBRANE.: Part of the epithelium, or outer layer of the cornea.
BECKER MUSCULAR DYSTROPHY (BMD).: A type of muscular dystrophy that affects older boys and men, and usually follows a milder course than Duchenne muscular dystrophy.
BECKWITH-WIEDEMANN SYNDROME.: A collection of health problems present at birth including an omphalocele, large tongue, and large body size.
BENIGN.: A non-cancerous tumor that does not spread and is not life-threatening.
BENIGN PROSTATIC HYPERPLASIA (BPH).: A noncancerous condition of the prostate that causes growth of the prostate tissue, thus enlarging the prostate and blocking urination.
BENIGN TUMOR.: An abnormal proliferation of cells that does not spread to other sites.
BENZOQUINONE ACETIC ACID.: Toxic compound that is formed when oxygen reacts with homogentisic acid.
BETA-2 MICROGLOBULIN.: A component protein of class I MHC.
BETA-ADRENERGIC BLOCKER.: A drug that works by controlling the nerve impulses along specific nerve pathways.
BETA CELLS.: Specialized cells of the pancreas that make insulin.
BIFID UVULA.: The uvula is the small, tear drop–shaped piece of flesh hanging in the back of the throat; the uvula is bifid if the bottom area is split in two parts.
BILATERAL.: Relating to or affecting both sides of the body or both of a pair of organs.
BILATERAL BREAST CANCER.: Cancer of both breasts, caused by two separate cancer processes.
BILE.: A substance produced by the liver, and concentrated and stored in the gallbladder. Bile contains a number of different substances, including bile salts, cholesterol, and bilirubin.
BILE ACIDS.: Steroid acids such as cholic acid that occur in bile, an alkaline fluid secreted by the liver and passed into a part of the small intestine where it aids in absorption of fats.
BILE ALCOHOL.: A steroid acid with an alcohol group attached.
BILE DUCT.: A passageway that carries bile (fluid secreted by the liver involved in fat absorption) from the liver to the gallbladder to the small intestine.
BILIRUBIN.: A yellow pigment that is the end result of hemoglobin breakdown. This pigment is metabolized in the liver and excreted from the body through the bile. Bloodstream levels are normally low; however, extensive red cell destruction leads to excessive bilirubin formation and jaundice.
BIOCHEMICAL TESTING.: Measuring the amount or activity of a particular enzyme or protein in a sample of blood or urine or other tissue from the body.
BIOFEEDBACK.: A technique in which patients are trained to gain some voluntary control over certain physiological conditions, such as blood pressure and muscle tension, and to promote relaxation.
BIOPSY.: The surgical removal and microscopic examination of living tissue for diagnostic purposes.
BIOPTICS.: Glasses that have small telescopes fitted in the lens.
BIOSYNTHESIS.: The manufacture of materials in a biological system.
BIOTIN.: A growth vitamin of the vitamin B complex found naturally in liver, egg yolks, and yeast.
BIPOLAR DISORDER.: Formerly called "manic depression," this psychological disorder is characterized by periods of mania followed by periods of depression.
BITEMPORAL CONSTRICTION.: Abnormal narrowing of both sides of the forehead.
BLACKFAN-DIAMOND SYNDROME (BDS).: A disorder with congenital hypoplastic anemia. Some researchers believe that some or all individuals with Aase syndrome actually have BDS, that Aase syndrome and BDS are not separate disorders.

BLADDER.: This is the organ that stores urine after it flows out of the kidneys and through the ureters.
BLEPHAROPHIMOSIS.: A small eye opening without fusion of the upper eyelid with the lower eyelid at the inner and outer corner of the eye.
BLEPHAROSPASM.: A focal dystonia marked by excessive blinking and involuntary closing of the eyes.
BLOOD VESSELS.: General term for arteries, veins, and capillaries which transport blood throughout the body.
BODY ASYMMETRY.: Abnormal development of the body in which the trunk and/or the limbs are not of equal size from one side of the body to the other.
BODY MASS INDEX (BMI).: Assessment of health related to weight and height.
BOILS.: Painful areas of inflammation.
BONE DYSPLASIA.: Abnormal bone development.
BONE MARROW TRANSPLANT (BMT).: A medical procedure used to treat some diseases that arise from defective blood cell formation in the bone marrow. Healthy bone marrow is extracted from a donor to replace the marrow in an ailing individual. Proteins on the surface of bone marrow cells must be identical or very closely matched between a donor and the recipient.
BONE MARROW.: A spongy tissue located in the hollow centers of certain bones, such as the skull and hip bones. Bone marrow is the site of blood cell generation.
BONE REMODELING.: The process of breaking down old bone and building up new bone.
BONE SCLEROSIS.: Increased bone density and hardness.
BOTULINUM TOXIN.: A class of neurotoxins that are produced by a bacteria and that cause paralysis and weakness of muscles.
BOWMAN'S LAYER.: Transparent sheet of tissue directly below the basement membrane.
BOY IN THE BUBBLE.: A description for SCID since these children need to be isolated from exposure to germs, until they are treated by bone marrow transplantation or other therapy.
BRACHYCEPHALY.: An abnormal thickening and widening of the skull.
BRACHYDACTYLY.: Abnormal shortness of the fingers and toes.
BRACHYMELIA.: A general medical term used to describe short limbs.
BRADYKINESIA.: Extremely slow movement.
BRAILLE.: An alphabet represented by patterns of raised dots which may be felt with the fingertips. It is the main method of reading used by the blind today.
BRAIN VENTRICLES.: A set of four connected cavities that are located deep in the core of the brain. Cerebrospinal fluid is made by cells lining the walls of the first two ventricles, then flows through the third, then fourth ventricle before flowing out of the brain. The fluid-filled cavities provide mechanical cushion for the brain, and the CSF provides nutrients to, and carries metabolic wastes away from, the cells of the brain.
BRANCHED-CHAIN.: An open chain of atoms having one or more side chains.
BRANCHING ENZYME.: Enzyme responsible for building the branched structure of glycogen stores.
BRCA1 AND BRCA2.: Genes that encode for proteins that supress tumor growth. Inherited mutations in these genes have been associated with hereditary forms of breast cancer.
BREAST BIOPSY.: Small sample of tissue taken from the breast and studied, to diagnose and determine the exact type of breast cancer.
BREAST SELF-EXAM (BSE).: Examination by an individual of their own breasts.
BREECH DELIVERY.: Birth of an infant feet or buttocks first.
BROAD LIGAMENT.: The ligament connecting the ovaries to the uterus.
BRONCHI.: Branching tube-like structures that carry air in and out of the lungs; walls of bronchi contain circular muscles that can constrict (tighten up to make airways narrower) or dilate (relax to make airways wider); bronchi divide into smaller bronchioles within the lung tissue.
BRONCHIECTASIS.: An abnormal condition of the bronchial tree, characterized by irreversible widening and destruction of the bronchial walls of the lungs.
BRUCH'S MEMBRANE.: A membrane in the eye between the choroid membrane and the retina.
BRUTON TYROSINE KINASE (BTK).: An enzyme vital for the maturation of B cells.
BULBAR MUSCLES.: Muscles that control chewing, swallowing, and speaking.
BUNDLES OF PROBST.: Abnormally developed nerve fibers in the brain.
BUNION.: A bulge on the first joint of the big toe, caused by the swelling of a fluid sac under the skin.

BUPHTHALMOS.: A characteristic enlargement of one or both eyes associated with infantile glaucoma.

C

C1 INHIBITOR.: Abbreviated C1-INH, this protein is responsible for preventing the action of the C1 complement molecules in the body. It is this protein that is either deficient or malformed in HANE.
CA-125 (CARBOHYDRATE ANTIGEN 125).: A protein that is sometimes high when ovarian cancer is present. A blood sample can determine the level of CA-125 present.
CAESAREAN SECTION.: Surgical method to deliver a baby that requires making an incision in the mother's abdomen to remove the infant.
CAFÉ-AU-LAIT SPOTS.: Birthmarks that may appear anywhere on the skin; named after the French coffee drink because of the light-brown color of the marks.
CALCIFICATION.: A process in which tissue becomes hardened due to calcium deposits.
CALCITRIOL.: A substance that assists in bone growth by helping to maintain calcium and phosphate levels in the blood. Vitamin D is converted into this substance by the body.
CALCIUM.: One of the elements that make up the hydroxyapatite crystals found in bone.
CAMPTODACTYLY.: An abnormal permanent bending of one or more fingers or toes.
CANAVAN DISEASE.: A serious genetic disease more common in the Eastern European Jewish population that causes mental retardation and early death. Canavan disease is caused by the lack of an enzyme called aspartoacylase.
CANCER.: A disease caused by uncontrolled growth of the body's cells.
CANCER CELLS.: Have characteristics that distinguish them from normal cells and non-cancerous cells; they are threatening, harmful, and resistant to treatment
CANDIDATE GENE.: A gene that encodes proteins believed to be involved in a particular disease process.
CAPILLARY.: Very narrow tube that carries liquid like blood or lymphatic fluid.
CARBOHYDRATE.: Any of various natural compounds of carbon, hydrogen, and oxygen (as in sugars and starches) that are burned by the body for energy.
CARCINOGEN.: Any substance capable of causing cancer by mutating the cell's DNA.
CARCINOMA.: Any cancer that arises in the epithelium, the tissue that lines the external and internal organs of the body.
CARDIAC CONDUCTION DEFECT.: Abnormality of the electrical system of the heart that regulates the heartbeat.
CARDIAC MUSCLE.: The muscle of the heart.
CARDINAL SYMPTOMS.: A group of symptoms that define a disorder or disease.
CARDIOMYOPATHY.: A thickening of the heart muscle.
CARNITINE PALMITOYLTRANSFERASE (CPT).: An enzyme that transfers a palmitoyl group. CPT is a major regulatory enzyme of lipid metabolism, required for the transport of long-chain fatty acids across the inner mitochondria membrane. This transport depends on carnitine.
CARNITINE.: An amino acid necessary for metabolism of the long-chain fatty acid portion of lipids. Also called vitamin B7.
CARRIER.: A person who possesses a gene for an abnormal trait without showing signs of the disorder. The person may pass the abnormal gene on to offspring. Also refers to a person who has a particular disease agent present within his or her body, and can pass this agent on to others, but who displays no symptoms of infection.
CARRIER TESTING.: Testing performed to determine if someone possesses one changed copy and one unchanged copy of a particular gene.
CARTILAGE.: A tough, elastic connective tissue found in the joints, outer ear, nose, larynx, and other parts of the body.
CARTILAGE OLIGOMERIC MATRIX PROTEIN GENE.: A gene that codes for a specific protein involved in the formation of cartilage.
CASEIN HYDROLYSATE.: A preparation made from the milk protein casein, which is hydrolyzed to break it down into its constituent amino acids. Amino acids are the building blocks of proteins.
CATAGEN.: The breakdown phase of the hair growth cycle.
CATALYST.: A substance that changes the rate of a chemical reaction, but is not physically changed by the process.
CATALYZE.: Facilitate. A catalyst lowers the amount of energy required for a specific chemical reaction to occur. Catalysts are not used up in the chemical reactions they facilitate.

CATAPLEXY.: A symptom of narcolepsy in which there is a sudden episode of muscle weakness triggered by emotions. The muscle weakness may cause the person's knees to buckle, or the head to drop. In severe cases, the patient may become paralyzed for a few seconds to minutes.
CATARACT.: A clouding of the eye's lens or its surrounding membrane that obstructs the passage of light and causes blurred vision. Surgery may be performed to remove the cataract.
CATATONIC BEHAVIOR.: Behavior characterized by muscular tightness or rigidity and lack of response to the environment. In some patients rigidity alternates with excited or hyperactive behavior.
CATECHOLAMINES.: Biologically active compounds involved in the regulation of the nervous and cardiovascular systems, rate of metabolism, body temperature, and smooth muscle.
CATHETER.: A narrow, flexible tube used to create a pathway for introducing drugs, nutrients, fluids, or blood products into the body and/or for removing fluid or other substances from the body.
CATHETERIZATION.: The process of inserting a hollow tube into a body cavity or blood vessel.
CATIONIC TRYPSINOGEN GENE.: Gene known to cause hereditary pancreatitis when significantly altered.
CAUDAL.: Pertaining to the tail (bone).
CAUTERIZATION.: Process of burning tissue either with a laser or electric needle to stop bleeding or destroy damaged tissue.
CDKN2A OR P16.: A gene that encodes for the tumorsupressing proteins p16 and p19. When this gene is altered it is known to cause familial atypical multiple mole melanoma (FAMMM) syndrome and possibly increased pancreatic cancer risk.
CECUM.: The first part of the large bowel.
CELL.: The smallest living units of the body which group together to form tissues and help the body perform specific functions.
CELL ADHESION MOLECULE.: Any one of several thousand proteins that together control the cell-to-cell communication that must take place in order for cells to migrate to their proper places, develop into the proper types of cells, and make the appropriate connections with other cells.
CELLULAR IMMUNITY.: A type of acquired immunity mediated by killer T-cells; important in fighting "hidden" infections, such as those caused by cellular parasites and some viruses.
CENTRAL NERVOUS SYSTEM.: Part of the nervous system consisting of the brain, cranial nerves, and spinal cord. The brain is the center of higher processes, such as thought and emotion and is responsible for the coordination and control of bodily activities and the interpretation of information from the senses. The cranial nerves and spinal cord link the brain to the peripheral nervous system, that is the nerves present in the rest of body.
CENTRAL POLYDACTYLY.: Occurring between the thumb and little finger or between the big toe and the little toe.
CENTRAL VISION.: The ability to see objects located directly in front of the eye. Central vision is necessary for reading and other activities that require people to focus on objects directly in front of them.
CENTROMERE.: The constricted region of a chromosome. It performs certain functions during cell division.
CEREBELLAR ATAXIA.: Unsteadiness and lack of coordination caused by a progressive degeneration of the part of the brain known as the cerebellum.
CEREBELLUM.: The lower back part of the brain responsible for functions such as maintaining balance, and coordinating and controlling voluntary muscle movement.
CEREBRAL CORTEX.: The outer surface of the cerebrum made up of gray matter and involved in higher thought processes.
CEREBRAL PALSY.: Movement disability resulting from nonprogressive brain damage.
CEREBRAL VENTRICLES.: Spaces in the brain that are located between portions of the brain and filled with cerebrospinal fluid.
CEREBRO.: Related to the head or brain.
CEREBROSIDES.: Fatty carbohydrates that occur in the brain and nervous system.
CEREBROSPINAL FLUID.: The clear, normally colorless fluid that fills the brain cavities (ventricles), the subarachnoid space around the brain, and the spinal cord and acts as a shock absorber.
CEREBRUM.: The largest section of the brain, which is responsible for such higher functions as speech, thought, vision, and memory.
CEROID.: The byproduct of cell membrane breakdown.
CERULOPLASMIN.: A protein circulating in the bloodstream that binds with copper and transports it.
CERVICAL DYSTONIA.: A focal dystonia that causes neck muscles to contract involuntarily, leading to abnormal movements and posture of the head and neck. Also known as spasmodic torticollis.

CERVICITIS.: Inflammation of the cervix.
CERVICO-MEDULLARY JUNCTION.: The area where the brain and spine connect.
CFTR.: Cystic fibrosis transmembrane conductance regulator. The protein responsible for regulating chloride movement across cells in some tissues. When a person has two defective copies of the CFTR gene, cystic fibrosis is the result.
CGG OR CGG SEQUENCE.: Shorthand for the DNA sequence: cytosine-guanine-guanine. Cytosine and guanine are two of the four molecules, otherwise called nucleic acids, that make up DNA.
CHAPERONIN.: A molecule that captures and refolds misshapen proteins that might interfere with normal cellular functions; also called a protein cage.
CHEMICAL METHYL GROUP.: One carbon and three hydrogen molecules that can be attached as a signal to DNA in the regulation of gene expression.
CHEMOTHERAPY.: Treatment of cancer with synthetic drugs that destroy the tumor either by inhibiting the growth of the cancerous cells or by killing the cancer cells.
CHIARI II ANOMALY.: A structural abnormality of the lower portion of the brain (cerebellum and brain stem) associated with spina bifida. The lower structures of the brain are crowded and may be forced into the foramen magnum, the opening through which the brain and spinal cord are connected.
CHOANAL ATRESIA.: A bony or membranous blockage of the passageway between the nose and pharynx at birth.
CHOLESTEROL.: A fatty-like substance that is obtained from the diet and produced by the liver. Cells require cholesterol for their normal daily functions.
CHOLINESTERASE.: Enzyme whose role is to break down released acetylcholine in the gap between nerve cells.
CHONDROCYTE.: A specialized type of cell that secretes the material which surrounds the cells in cartilage.
CHONDROSARCOMA.: A malignant tumor derived from cartilage cells.
CHOREA.: Involuntary, rapid, jerky movements.
CHOREOATHETOSIS.: Involuntary rapid, irregular, jerky movements or slow, writhing movements that flow into one another.
CHORIOCAPILLARIS.: Capillary layer of the choroid.
CHORION.: The outer membrane of the amniotic sac. Chorionic villi develop from its outer surface early in pregnancy. The villi establish a physical connection with the wall of the uterus and eventually develop into the placenta.
CHORIONIC VILLUS SAMPLING (CVS).: A procedure used for prenatal diagnosis at 10-12 weeks gestation. Under ultrasound guidance a needle is inserted either through the mother's vagina or abdominal wall and a sample of cells is collected from around the early embryo. These cells are then tested for chromosome abnormalities or other genetic diseases. Also known as chorionic villus biopsy.
CHOROID.: In the human eye, the thin layer of tissue that lies between the sclera and the retina. The choroid is rich in blood vessels that nourish the retina, and the dark pigments of the choroid absorb light rays so that they are not reflected back out of the eye.
CHOROID PLEXUS.: Specialized cells located in the ventricles of the brain that produce cerebrospinal fluid.
CHROMATID.: Each of the two strands formed by replication of a chromosome. Chromatids are held together by the centromere until the centromere divides and separates the two chromatids into a single chromosome.
CHROMOSOMAL ANEUPLODIES.: A condition in which the chromosomal number is either increased or decreased.
CHROMOSOME.: A microscopic thread-like structure found within each cell of the human body and consisting of a complex of proteins and DNA. Humans have 46 chromosomes arranged into 23 pairs. Chromosomes contain the genetic information necessary to direct the development and functioning of all cells and systems in the body. They pass on hereditary traits from parents to child (like eye color) and determine whether the child will be male or female.
CHROMOSOME DELETION.: A missing sequence of DNA or part of a chromosome.
CHROMOSOME INVERSION.: Rearrangement of a chromosome in which a section of a chromosome breaks off and rejoins the chromosome upside down.
CHROMOSOME TRANSLOCATION.: The exchange of genetic material between chromosomes, which can lead to extra or missing genetic material.
CHRONIC ATROPHIC GASTRITIS.: Irritation and break down of the stomach wall over a period of time.

CHYLOMICRON.: A type of lipoprotein made in the small intestine and used for transporting fats to other tissues in the body.
CILIARY BODY.: A structure within the eye that produces aqueous humor.
CIRCUMCISION.: The surgical removal of the fore-skin of the penis.
CIRRHOSIS.: A chronic degenerative disease of the liver in which normal cells are replaced by fibrous tissue. Cirrhosis is a major risk factor for the later development of liver cancer.
CLASS I MHC.: Major histocompatibility complex class I includes HLA-A, HLA-B, and HLA-C. These are proteins important in cellular immunity.
CLASS II MHC.: Major histocompatibility complex class II includes HLA-DP, HLA-DQ, and HLA-DR. These are proteins important in humoral immunity.
CLASS III MHC.: Major histocompatibility complex class III includes the complement system.
CLAUDICATION.: Pain in the lower legs after exercise caused by insufficient blood supply.
CLAVICLE.: Also called the collarbone. Bone that articulates with the shoulder and the breast bone.
CLEFT.: An elongated opening or slit in an organ.
CLEFT LIP.: A separation of the upper lip that is present from birth but originates early in fetal development. A cleft lip may appear on one side (unilateral) or both sides (bilateral) and is occasionally accompanied by a cleft palate. Surgery is needed to completely repair cleft lip.
CLEFT PALATE.: A congenital malformation in which there is an abnormal opening in the roof of the mouth that allows the nasal passages and the mouth to be improperly connected.
CLINICAL BREAST EXAM (CBE).: Examination of the breasts, performed by a physician or nurse.
CLINICAL TRIAL.: The testing of a drug or some other type of therapy in a specific population of patients.
CLINODACTYLY.: An abnormal inward curving of the fingers or toes.
CLITORIS.: A small mass of erectile tissue in the female genitalia.
CLONE.: A cell or organism derived through asexual (without sex) reproduction containing the identical genetic information of the parent cell or organism.
CLONUS.: A sustained series of involuntary rhythmic jerks following quick stretch of a muscle.
CLOSED-ANGLE GLAUCOMA.: An increase in the fluid pressure within the eye due to a complete, and sometimes sudden, blockage of the fluid drainage passages.
CLOVERLEAF SKULL.: An abnormal, or cloverleaf, appearance to the skull caused by premature fusion of the bones in the skull of an infant.
CLUBFOOT.: Abnormal permanent bending of the ankle and foot. Also called talipes equinovarus.
CO-DOMINANT.: Describes the state when two alleles of the same gene are both expressed when inherited together.
CO-ENZYME.: A small molecule such as a vitamin that works together with an enzyme to direct a biochemical reaction within the body.
COAGULATION.: Generally, the solidification or change from a fluid state to a semisolid mass. More specifically, the entire process of blood clotting; blood coagulation helps to close open wounds.
COAGULOPATHY.: A disorder in which blood is either too slow or too quick to coagulate (clot).
COARCTATION.: A narrowing of the aorta that is often associated with bicuspid aortic valve.
COBB ANGLE.: A measure of the curvature of scoliosis, determined by measurements made on x rays.
COCHLEA.: A bony structure shaped like a snail shell located in the inner ear. It is responsible for changing sound waves from the environment into electrical messages that the brain can understand, so people can hear.
COCHLEAR IMPLANTATION.: A surgical procedure in which a small electronic device is placed under the skin behind the ear and is attached to a wire that stimulates the inner ear, allowing people who have hearing loss to hear useful sounds.
COFACTOR.: A substance that is required by an enzyme to perform its function.
COGNITION.: The mental activities associated with thinking, learning, and memory.
COGNITIVE.: Brain functions involved in the ability to think, learn, and remember.
COGNITIVE/BEHAVIORAL THERAPIES.: Psychological counseling that focuses on changing the behavior of the patient.
COLCHICINE.: A compound that blocks the assembly of microtubules—protein fibers necessary for cell division and some kinds of cell movements, including neutrophil migration. Side effects may include diarrhea, abdominal bloating, and gas.

COLECTOMY.: Surgical removal of the colon.
COLITIS.: Inflammation of the colon.
COLLAGEN.: The main supportive protein of cartilage, connective tissue, tendon, skin, and bone.
COLOBOMA.: A birth defect in which part of the eye is absent or does not form completely.
COLON.: The large intestine.
COLONOSCOPY.: Procedure for viewing the large intestine (colon) by inserting an illuminated tube into the rectum and guiding it up the large intestine.
COLORECTAL.: Of the colon and/or rectum
COLOSTOMY.: The creation of an artificial opening into the colon through the skin for the purpose of removing bodily waste. Colostomies are usually required because key portions of the intestine have been removed.
COMPLEMENT SYSTEM.: Class III MHC (major histocompatobility complex) proteins capable of destroying invading organisms directly via natural immunity, as well as indirectly through an interaction with other components of the immune system.
COMPLETE SITUS INVERSUS.: A laterality defect resulting in a mirror image of the normal organ formation with heart, spleen, and stomach on the right, and the liver and gallbladder on the left side.
COMPOUND HETEROZYGOTE.: Having two different mutated versions of a gene.
COMPUTED TOMOGRAPHY (CT).: An imaging technique in which cross-sectional x rays of the body are compiled to create a three-dimensional image of the body's internal structures; also called computed axial tomography.
COMT INHIBITORS.: Drugs that block catechol-O-methyltransferase, an enzyme that breaks down dopamine. COMT inhibitors include entacapone and tolcapone.
CONCEPTUS.: The products of conception, or the union of a sperm and egg cell at fertilization.
CONCORDANCE.: When two individuals have the same disease, such as when identical twins both have diabetes.
CONDUCTIVE HEARING LOSS.: Hearing loss that is the result of a dysfunction of the parts of the ear responsible for collecting sound. In this type of hearing loss, the auditory nerve is generally not damaged.
CONES.: Receptor cells that allow the perception of colors.
CONGENITAL.: Present at birth.
CONGENITAL ANOMALY.: An abnormality that is present at birth.
CONGENITAL CATARACT.: Clouding of the lens in the eye that is present at birth.
CONGENITAL HEART DISEASE.: Structural abnormality of the heart at birth. Examples include a ventricular septal defect and atrial septal defect.
CONGENITAL HYPOPLASTIC ANEMIA (CHA).: A significant reduction in the number of red blood cells present at birth, usually referring to deficient production of these cells in the bone marrow. Also sometimes called congenital aplastic anemia.
CONNECTIVE TISSUE.: A group of tissues responsible for support throughout the body; includes cartilage, bone, fat, tissue underlying skin, and tissues that support organs, blood vessels, and nerves throughout the body.
CONNEXIN.: A protein that joins cells together and allows them to exchange small substances.
CONOTRUNCAL HEART ABNORMALITY.: Congenital heart defects particularly involving the ventricular (lower chambers) outflow tracts of the heart includes subarterial ventricular septal defect, pulmonic valve atresia and stenosis, tetralogy of Fallot and truncus arteriosus.
CONSANGUINEOUS.: Sharing a common bloodline or ancestor.
CONSANGUINITY.: A mating between two people who are related to one another by blood.
CONTINENCE.: Normal function of the urinary bladder and urethra, allowing fluid flow during urination and completely stopping flow at other times.
CONTINGUOUS GENE DELETION SYNDROME.: A genetic disorder due to the deletion of a number of genes that lie close to one another on a specific chromosome.
CONTINGUOUS GENE SYNDROME.: Conditions that occur as a result of microdeletions or microduplications involving several neighboring genes.
CONTRACTURE.: A tightening of muscles that prevents normal movement of the associated limb or other body part.
CONVULSION.: Involuntary contractions of body muscles that accompany a seizure episode.
COPROLALIA.: The involuntary expression of obscene words or phrases.
COPROPRAXIA.: The involuntary display of unacceptable/obscene gestures.

CORDOCENTESIS.: A prenatal diagnostic test, usually done between 16-30 weeks of gestation. Using ultrasound guidance, a thin needle is introduced through the abdomen into the amniotic sac. A blood sample is taken directly from the umbilical cord. Tests can then be done on the blood sample.
CORNEA.: The clear, dome-shaped outer covering of the eye that lies in front of the iris and pupil. The cornea lets light into the eye.
CORNEAL TRANSPLANT.: Removal of impaired and diseased cornea and replacement with corneal tissue from a recently deceased person.
CORONAL SUTURE.: Skull suture that lies behind the forehead area, across the head from left side to the right side.
CORPORA ALBICANTIA.: Plural of corpus albicans. The scar tissue that remains on an ovarian follicle after ovulation.
CORPUS CALLOSUM.: A thick bundle of nerve fibers deep in the center of the forebrain that provides communications between the right and left cerebral hemispheres.
CORTICOSPINAL TRACT.: A tract of nerve cells that carries motor commands from the brain to the spinal cord.
CORTICOSTEROIDS.: Anti-inflammatory medications. Related to cortisol, a naturally produced hormone that controls many body functions.
COXA VARA.: A deformed hip joint in which the neck of the femur is bent downward.
CRANIAL NERVES.: The twelve nerves that originate in the brain, and control functions such as hearing, vision and facial expression.
CRANIAL SUTURE.: Any one of the seven fibrous joints between the bones of the skull.
CRANIOFACIAL.: Relating to or involving both the head and the face.
CRANIOPAGUS.: Conjoined wins with separate bodies and one shared head.
CRANIOPHARYNGIOMA.: A tumor near the pituitary gland in the craniopharyngeal canal that often results in intracranial pressure.
CRANIOSYNOSTOSIS.: A premature closure of one or more of the joints (fissures) between the bones of the skull, which causes an abnormally shaped skull.
CRANIUM.: The skeleton of the head, which include all of the bones of the head except the mandible.
CREATINE KINASE (CK).: An enzyme that is normally found in the skeletal or voluntary muscle and cardiac muscle; very high levels in the blood usually indicate breakdown of either heart or voluntary muscle.
CREATININE.: The metabolized by-product of creatine, an organic acid that assists the body in producing muscle contractions. Creatinine is found in the bloodstream and in muscle tissue. It is removed from the blood by the kidneys and excreted in the urine. Higher than normal levels of this substance may indicate kidney disease.
CREUTZFELDT-JAKOB DISEASE.: A degenerative disease of the central nervous system caused by a prion, or "slow virus."
CRI DU CHAT SYNDROME.: A syndrome caused by a deletion in chromosome 5; characterized by a strange cry that sounds like the mewing of a cat.
CRYPTOPHTHALMOS.: An abnormal formation of the eye in which the eyelid, or overlaying skin of the eye, is fused shut. Literally, "hidden eye."
CRYPTORCHIDISM.: Undescended testes, a condition in which a boy is born with one or both testicles in the lower abdomen rather than the scrotum.
CURETTAGE.: A surgical scrapping or cleaning.
CUTANEOUS.: Of, pertaining to, or affecting the skin.
CUTANEOUS SYNDACTYLY.: Fusion of the soft tissue between fingers or toes resulting in a webbed appearance.
CYANOSIS.: A bluish tinge to the skin that can occur when the blood oxygen level drops too low.
CYCLOOXYGENASE-2 (COX-2) INHIBITORS.: Anti-inflammatory drugs that work by blocking the COX-2 enzyme, which plays a role in the inflammatory process, but do not block the COX-1 enzyme, which helps protect the digestive tract.
CYDROCEPHALY.: Excessive accumulation of cerebral spinal fluid in the brain ventricles.
CYST.: An abnormal sac or closed cavity filled with liquid or semisolid matter.
CYSTIC FIBROSIS.: A respiratory disease characterized by chronic lung disease, pancreatic insufficiency and an average age of survival of 20 years. Cystic fibrosis is caused by mutations in a gene on chromosome 7 that encode a transmembrane receptor.
CYSTIC HYGROMA.: An accumulation of fluid around the head and neck caused by the blockage of drainage of lymphatic fluid.

CYSTIC HYGROMA.: An accumulation of fluid behind the fetal neck, often caused by improper drainage of the lymphatic system in utero.
CYSTIC HYGROMA.: Birth defect that appears as a soft bulging under the skin at the neck; the bulging is actually abnormal growths of sac-like structures filled with lymphatic fluid.
CYSTINE.: A sulfur-containing amino acid, sometimes found as crystals in the kidneys or urine, that forms when proteins are broken down by digestion.
CYTOKINES.: Chemicals made by the cells that act on other cells to stimulate or inhibit their function. They are important controllers of immune functions. At high levels, cytokines may be toxic to nerve cells in the developing brain.
CYTOPLASM.: The substance within a cell including the organelles and the fluid surrounding the nucleus.
CYTOSKELETON.: The network of proteins underlying and maintaining the integrity of the red blood cell membrane.

D

DANDY-WALKER MALFORMATION.: A complex structural abnormality of the brain frequently associated with hydrocephalus, or accumulation of excess fluid in the brain. Abnormalities in other areas of the body may also be present. Individuals with Dandy-Walker malformation have varying degrees of mental handicap, or none at all.
DE NOVO.: Latin term for new.
DE NOVO DELETION.: A deletion that occurs for the first time in the affected individual. The cause of de novo deletions is not known.
DE NOVO MUTATION.: Genetic mutations that are seen for the first time in the affected person, not inherited from the parents.
DEBRANCHING ENZYME.: Enzyme responsible for breaking down the branched structure of glycogen stores to release glucose into the bloodstream.
DECIDUOUS TEETH.: The first set of teeth or "baby teeth."
DECREASED PENETRANCE.: Individuals who inherit a changed disease gene but do not develop symptoms.
DEEP VEIN THROMBOSIS.: A blood clot in one of the systemic veins deep in the body.
DEFORMATION.: Abnormal shape or function in otherwise normal tissue produced by unusual mechanical forces on the embryo/fetus.
DEGENERATION.: Nerves progressively withering.
DEGENERATIVE DISC DISEASE.: Narrowing of the disc space between the spinal bones (vertebrae).
DEGENERATIVE DISORDER.: A disorder by which the body or a part of the body gradually loses its ability to fucntion.
DEGRADATION.: Loss or diminishing.
DEHYDRATION.: An extreme loss of water in the body which, if untreated, can lead to brain damage and death.
DELAYED BONE AGE.: an abnormal condition in which the apparent age of the bones, as seen in x rays, is less than the chronological age of the patient.
DELETION.: The absence of genetic material that is normally found in a chromosome. Often, the genetic material is missing due to an error in replication of an egg or sperm cell.
DELIRIUM.: A disturbance of consciousness marked by confusion, difficulty paying attention, delusions, hallucinations, or restlessness. It can be distinguished from dementia by its relatively sudden onset and variation in the severity of the symptoms.
DELUSION.: A fixed, false belief that is resistant to reason or factual disproof.
DEMENTIA.: Loss of memory and other higher functions, such as thinking or speech, lasting six months or more.
DEOXYRIBONUCLEIC ACID (DNA).: The genetic material in cells that holds the inherited instructions for growth, development, and cellular functioning.
DEPIGMENTATION.: Loss of pigment or skin color.
DEPOLARIZATION.: The dissipation of an electrical charge through a membrane. In the heart, depolarization causes the heart muscle to contract.
DEPOT DOSAGE.: A form of medication that can be stored in the patient's body tissues for several days or weeks, thus minimizing the risk of the patient forgetting daily doses.
DEPRIVATIONAL DWARFISM.: A condition where emotional disturbances are associated with growth failure and abnormalities of pituitary function.
DERMATOLOGIC.: Pertaining to the field of dermatology, the science of the skin and diseases that affect the skin.

DERMATOLOGIST.: A physician that specializes in disorders of the skin.
DERMATOSPARAXIS.: Skin fragility caused by abnormal collagen.
DERMIS.: The layer of skin beneath the epidermis.
DESCEMET'S MEMBRANE.: Sheet of tissue that lies under the stroma and protects against infection and injuries.
DESFEROXAMINE.: The primary drug used in iron chelation therapy. It aids in counteracting the life-threatening buildup of iron in the body associated with long-term blood transfusions.
DESMOID TUMOR.: Benign, firm mass of scarlike connective tissue
DESMOPRESSIN (DDAVP).: A drug used in the treatment of von Willebrand's disease.
DEUTERANOPIA.: The inability or difficulty in distinguishing red/green colors.
DEVELOPMENT.: The process whereby undifferentiated embryotic cells replicate and differentiate into limbs, organ systems, and other body components of the fetus.
DEVELOPMENTAL DELAY.: The failure of a child to meet certain developmental milestones, such as sitting, walking, and talking, at the average age. Developmental delay may indicate a problem in development of the central nervous system.
DEVELOPMENTAL MILESTONES.: Infants and toddlers develop skills at certain ages. For example, by nine months, a child should be able to grasp and toss a bottle.
DEXTROCARDIA.: Defect in which the position of the heart is the mirror image of its normal position.
DIABETES.: An inability to control the levels of sugar in the blood due to an abnormality in the production of, or response to, the hormone insulin.
DIABETES MELLITUS.: The clinical name for common diabetes. It is a chronic disease characterized by the inability of the body to produce or respond properly to insulin, a hormone required by the body to convert glucose to energy.
DIAGNOSTIC TESTING.: Testing performed to determine if someone is affected with a particular disease.
DIALYSIS.: A process of filtering and removing waste products from the bloodstream, it is used as a treatment for patients whose kidneys do not function properly. Two main types are hemodialysis and peritoneal dialysis. In hemodialysis, the blood flows out of the body into a machine that filters out the waste products and routes the cleansed blood back into the body. In peritoneal dialysis, the cleansing occurs inside the body. Dialysis fluid is injected into the peritoneal cavity and wastes are filtered through the peritoneum, the thin membrane that surrounds the abdominal organs.
DIAPHRAGMATIC HERNIA.: An abnormal opening in the diaphragm, the layer of muscle that separates the chest cavity from the abdominal cavity. The intestines are herniated through the diaphragm into the chest cavity.
DIAPHYSIS.: The middle portion, or shaft, of a long bone.
DIARRHEA.: Loose, watery stool.
DIASTOLIC BLOOD PRESSURE.: Blood pressure when the heart is resting between beats.
DICEPHALUS.: Conjoined twins who share one body but have two separate heads and necks.
DIFFERENTIATE.: Specialized development to perform a particular function.
DIGESTIVE ENZYME.: Proteins secreted by the pancreas that enter the small intestine and break down food so it can be absorbed by the body.
DIGIT.: A finger or toe.
DIHYDROTESTOSTERONE (DHT).: A male sex hormone formed from testosterone by the enzyme 5-alpha-reductase. DHT causes hair follicles to shut down, shortening the growth phase of the hair growth cycle and leading to miniaturization.
DILATED CARDIOMYOPATHY.: A diseased and weakened heart muscle that is unable to pump blood efficiently.
DIOPTER (D).: A unit of measure for describing refractive power.
DIPLEGIA.: Paralysis affecting like parts on both sides the body, such as both arms or both legs.
DIPLOID.: Means "double number." The normal number of chromosomes (two) for all cells of the human body, except for the sex cells.
DISRUPTION.: A type of anomaly formation in which a breakdown or inhibition of normal tissue development occurs.
DISTAL.: Away from the point of origin, midline, or central point.
DISTAL ARTHROGRYPOSIS.: A disorder characterized by contractions of the muscles in the hands.
DISTAL MUSCLES.: Muscles that are furthest away from the center of the body.

DISTAL MUSCULAR DYSTROPHY (DD).: A form of muscular dystrophy that usually begins in middle age or later, causing weakness in the muscles of the feet and hands.
DISULFIRAM.: A medication that has been used since the late 1940s as part of a treatment plan for alcohol abuse. Disulfiram, which is sold under the trade name Antabuse, produces changes in the body's metabolism of alcohol that cause headaches, vomiting, and other unpleasant symptoms if the patient drinks even small amounts of alcohol.
DIURETICS.: Medications that increase the excretion of urine.
DIVERTICULAE.: Sacs or pouches in the walls of a canal or organ. They do not normally occur, but may be acquired or present from birth. Plural form of diverticula.
DIZYGOTIC.: From two zygotes, as in non-identical, or fraternal twins. The zygote is the first cell formed by the union of sperm and egg.
DNA.: Deoxyribonucleic acid, inheritable material that constitutes the building blocks of life.
DNA MUTATION ANALYSIS.: A direct approach to the detection of a specific genetic mutation or mutations using one or more laboratory techniques.
DNA REPEATS.: A three letter section of DNA, called a triplet, which is normally repeated several times in a row. Too many repeats often cause the gene to not function properly, resulting in disease.
DNA TESTING.: Analysis of DNA (the genetic component of cells) in order to determine mutations in genes that may indicate a specific disorder.
DOLICOCEPHALY.: Elongated and narrow skull shape due to premature closure of the sagittal suture that runs from the forehead to the back of the skull.
DOMINANT GENE.: A gene, whose presence as a single copy, controls the expression of a trait.
DOMINANT INHERITANCE.: A type of genetic inheritance pattern results in one form of a gene being dominant over other forms. Therefore, the dominant allele can express itself and cause disease, even if only one copy is present.
DOMINANT PROGRESSIVE HEARING LOSS.: The main type of non-syndromic progressive sensorineural hearing loss seen in humans.
DOMINANT TRAIT.: A genetic trait where one copy of the gene is sufficient to yield an outward display of the trait; dominant genes mask the presence of recessive genes; dominant traits can be inherited from a single parent.
DOPAMINE RECEPTOR ANTAGONISTS (DAS).: The older class of antipsychotic medications, also called neuroleptics, which primarily block the site on nerve cells that normally receive the brain chemical dopamine.
DOPAMINE.: A neurochemical made in the brain that is involved in many brain activities, including movement and emotion.
DORSAL RHIZOTOMY.: A surgical procedure that cuts nerve roots to reduce spasticity in affected muscles.
DORSAL ROOT GANGLIA.: The subset of neuronal cells controlling impulses in and out of the brain.
DOWN SYNDROME.: A genetic condition characterized by moderate to severe mental retardation, a characteristic facial appearance, and, in some individuals, abnormalities of some internal organs. Down syndrome is always caused by an extra copy of chromosome 21, or three rather than the normal two. For this reason, Down syndrome is also known as trisomy 21.
DOWNSHOOT.: Downward movement of the eye.
DRPLA.: Dentatorubral-pallidoluysian atrophy; also called Haw River syndrome and Natito-Oyanagi disease. DRPLA is a disorder of ataxia, choreoathetosis, and dementia in adults, and ataxia, myoclonus, epilepsy, and mental retardation in children.
DRUSEN.: Fatty deposits that can accumulate underneath the retina and macula, and sometimes lead to agerelated macular degeneration (AMD). Drusen formation can disrupt the photoreceptor cells, which causes central and color vision problems for people with dry AMD.
DUCHENNE MUSCULAR DYSTROPHY (DMD).: The most severe form of muscular dystrophy, DMD usually affects young boys and causes progressive muscle weakness, usually beginning in the legs.
DUCT.: Tube-like structure that carries secretions from glands.
DUCTUS.: The blood vessel that joins the pulmonary artery and the aorta. When the ductus does not close at birth, it causes a type of congenital heart disease called patent ductus arteriosus.
DUCTUS ARTERIOSUS.: The temporary channel or blood vessel between the aorta and pulmonary artery in the fetus.
DUODENUM.: Portion of the small intestine nearest the stomach; the first of three parts of the small intestine.
DUPLICATION.: A type of chromosomal defect in which a broken segment of a chromosome attaches to the chromosome pair resulting in extra chromosomal material.

DWARFISM.: Any condition that results in extremely shortened limbs.
DYSARTHRIA.: Slurred speech.
DYSGENESIS.: Defective or abnormal formation of an organ or part usually occuring during embryonic development.
DYSKINESIA.: Impaired ability to make voluntary movements.
DYSMORPHIC.: Literally meaning misshapen, it is most often used as a general descriptive term for anomalous physical characteristics.
DYSMORPHIC FEATURE.: A change in appearance such as low set ears or a flattened nasal bridge that suggests a genetic syndrome may be present.
DYSOSTOSIS MULTIPLEX.: A variety of bone and skeletal malformations.
DYSPHORIA.: Feelings of anxiety, restlessness, and dissatisfaction.
DYSPLASIA.: Abnormal development of tissues, organs, or cells.
DYSTHYMIA.: A psychological condition of chronic depression that is not disabling, but prevents the sufferer from functioning at his or her full capacity.
DYSTONIA.: Painful involuntary muscle cramps or spasms.
DYSTOPIA CANTHORUM.: A wide spacing between the inner corners of the eyes, with the eyes themselves having normal spacing. Also called telecanthus.
DYSTROPHIN.: A protein that helps muscle tissue repair itself. Both Duchenne muscular dystrophy and Becker muscular dystrophy are caused by flaws in the gene that instructs the body how to make this protein.
DYSTROPHY.: Progressive abnormal changes in a tissue or organ.

E

E-CADHERIN/CDH1.: A gene involved in cell-to-cell connection. Alterations in this gene have been found in several families with increased rates of gastric cancer.
EAR TAGS.: Excess pieces of skin on the outside of the ear.
EARLY ON SET DYSTONIA.: Dystonia that begins in adolescence. Most common among Jews of Eastern European ancestry.
ECHOCARDIOGRAPHY.: A non-invasive technique that uses ultrasonic waves to look at the various structures and functions of the heart. The image obtained with this technique is called an echocardiogram.
ECHOLALIA.: Involuntary echoing of the last word, phrase, or sentence spoken by someone else.
ECHOPRAXIA.: The imitation of the movement of another individual.
ECTODERM.: The outermost of the three embryonic cell layers, which later gives rise to the skin, hair, teeth, and nails. These are cells affected in Ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome.
ECTODERMAL DYSPLASIA.: A hereditary condition that results in the malformation of the skin, teeth, and hair. It is often associated with malfunctioning or absent sweat glands and/or tear ducts.
ECTOPIA LENTIS.: Dislocation of the lens of the eye. It is one of the most important single indicators in diagnosing Marfan syndrome.
ECTOPIC.: Tissue found in an abnormal location.
ECTRODACTYLY.: A birth defect involving a split or cleft appearance of the hands or feet, also referred to as a "lobster-claw malformation."
ECZEMA.: Inflammation of the skin with redness and other variable signs such as crusts, watery discharge, itching.
EDEMA.: Extreme amount of watery fluid that causes swelling of the affected tissue.
EDWARDS SYNDROME.: A syndrome caused by trisomy 18; characterized by multi-system defects; and usually lethal by age 1.
EFFLUVIUM.: The medical term for massive hair loss or shedding.
ELASTIC FIBER.: Fibrous, stretchable connective tissue made primarily from proteins, elastin, collagen, and fibrillin.
ELASTIN.: A protein that gives skin the ability to stretch and then return to normal.
ELECTROCARDIOGRAM (ECG, EKG).: A test used to measure electrical impulses coming from the heart in order to gain information about its structure or function.
ELECTROCONVULSIVE THERAPY.: A psychological treatment in which a series of controlled electrical impulses are delivered to the brain in order to induce a seizure within the brain.

ELECTROLYTE.: A solution or a substance in a solution consisting of various chemicals that can carry electric charges. They exist in the blood as acids, bases, and salts, such as sodium, calcium, potassium, chlorine, and magnesium.
ELECTROMYOGRAPHY (EMG).: A diagnostic test that records the electrical activity of muscles. In the test, small electrodes are placed on or in the skin; the patterns of electrical activity are projected on a screen or over a loudspeaker. This procedure is used to test for muscle disorders, including muscular dystrophy.
ELECTRORETINOGRAPHY (ERG).: A diagnostic test that records electrical impulses created by the retina when light strikes it.
EMBOLIZATION THERAPY.: Introduction of various substances into the circulation to plug up blood vessels in order to stop bleeding.
EMBRYO.: The earliest stage of development of a human infant, usually used to refer to the first eight weeks of pregnancy. The term fetus is used from roughly the third month of pregnancy until delivery.
EMBRYOGENESIS.: The formation and growth of the embryo.
EMOLLIENT.: Petroleum or lanolin based skin lubricants.
EMPHYSEMA.: A chronic lung disease that begins with breathlessness during exertion and progresses to shortness of breath at all times, caused by destructive changes in the lungs.
ENCAPSULATED.: Referring to bacteria that have a thick capsule protecting their cell wall.
ENCEPHALOCELE.: A gap in the skull through which membranes and brain tissue may protrude.
ENCEPHALOPATHY.: A degenerative disease of the brain that has a sudden onset.
ENCHONDROMAS.: Benign cartilaginous tumors arising in the cavity of bone. They have the possibility of causing lytic destruction within the bone.
ENDOCARDITIS.: A dangerous infection of the heart valves caused by certain bacteria.
ENDOCRINE SYSTEM.: A system of ductless glands that regulate and secrete hormones directly into the bloodstream.
ENDOLYMPH.: The fluid in the inner ear.
ENDOSCOPIC RETROGRADE CHOLANGIOPANCREATOGRAPHY (ERCP).: A method of viewing the pancreas by inserting a thin tube down the throat into the pancreatic and bile ducts, injection of dye, and performing x rays.
ENDOSCOPY.: A slender, tubular optical instrument used as a viewing system for examining an inner part of the body and, with an attached instrument, for biopsy or surgery.
ENDOSTEAL.: Relating to the endosteum, which is the lining of the medullary cavity.
ENDOTHELIAL CELLS.: The cells lining the inner walls of the blood vessels.
ENDOTHELIUM.: Extremely thin innermost layer of the cornea.
ENLARGED VESTIBULAR AQUEDUCT (EVA).: An enlargement of a structure inside the inner ear called the vestibular aqueduct, which is a narrow canal that allows fluid to move within the inner ear. EVA is seen in approximately 10% of people who have sensorineural hearing loss.
ENTEROCOLITIS.: Severe inflammation of the intestines that affects the intestinal lining, muscle, nerves and blood vessels.
ENTEROSCOPY.: A procedure used to examine the small intestine.
ENTEROVIRUS.: Any of a group of viruses that primarily affect the gastrointestinal tract.
ENTHESITIS.: Inflammation at the place where the ligaments insert into the bone.
ENTHESOPATHY.: Disorder of the ligament attachment to the bone.
ENZYMATIC/ENZYME REPLACEMENT THERAPY.: A treatment method used to replace missing enzymes. It is possible to synthesize enzymes and then inject them intravenously into patients.
ENZYME.: A protein that catalyzes a biochemical reaction or change without changing its own structure or function.
ENZYME EFFICIENCY.: The rate at which an enzyme can perform the chemical transformation it is expected to accomplish. This is also called turnover rate.
EPENDYMOMA.: Tumor of the central nervous system derived from cells that line the central canal of the spinal cord and the ventricles of the brain.
EPIBULBAR DERMOIDS.: Cysts on the eyeball.
EPICANTHAL FOLD.: Fold of skin extending from the eyelid over the inner corner of the eye.

EPIDERMIS.: The outermost layer of the skin.
EPIDERMOID CYST.: Benign, cystic tumor derived from epithelial cells.
EPIDIDYMUS.: Coiled tubules that are the site of sperm storage and maturation for motility and fertility. The epididymis connects the testis to the vas deferens.
EPIGENETIC.: Implying a modification outside of actual mutation of the DNA sequence, such as the addition of a methyl group.
EPILEPSY.: A neurological disorder characterized by recurrent seizures with or without a loss of consciousness.
EPIPHYSIS.: The end of a long bone, usually terminating in a joint.
EPITHELIAL CELLS.: The layer of cells that cover the open surfaces of the body such as the skin and mucous membranes.
EPITHELIUM.: The layer of cells that cover the open surfaces of the body such as the skin and mucous membranes.
ERYTHEMA.: Redness of the skin due to dilatation of capillaries.
ERYTHEMA NODOSUM LEPROSUM.: A complication of leprosy characterized by development of painful small swellings due to inflammation of a blood or lymph vessel. It is often accompanied by inflammation of a nerve or nerves, causing decreased function of the affected area.
ERYTHROPOIESIS.: The process through which new red blood cells are created; it begins in the bone marrow.
ERYTHROPOIETIC.: Referring to the creation of new red blood cells.
ESOPHAGUS.: The part of the digestive tract which connects the mouth and stomach; the foodpipe.
ESTROGEN.: A female sex hormone.
ETHANOL.: The chemical name for beverage alcohol. It is also sometimes called ethyl alcohol or grain alcohol to distinguish it from isopropyl or rubbing alcohol.
ETIOLOGY.: The cause of a disease, syndrome, or anomaly.
EUGENICS.: A social movement in which the population of a society, country, or the world is to be improved by controlling the passing on of hereditary information through mating.
EVOKED RESPONSE TESTS.: Tests that measure the speed of brain connections.
EXCISION.: Surgical removal.
EXOCRINE PANCREAS.: The secreting part of the pancreas.
EXOMPHALOS.: An umbilical protrusion or hernia.
EXON.: The expressed portion of a gene. The exons of genes are those portions that actually chemically code for the protein or polypeptide that the gene is responsible for producing.
EXOSTOSIS.: An abnormal growth (benign tumor) on a bone.
EXPANSION.: A genetic abnormality caused by a sequence of nucleotides that is repeated too many times in a section of a gene.
EXTERNAL MEATUS.: The external opening through which urine and seminal fluid (in males only) leave the body.
EXTRAOCULAR MUSCLE FIBROSIS.: Abnormalities in the muscles that control eye movement.
EXTRAPYRAMIDAL SYMPTOMS (EPS).: A group of side effects associated with antipsychotic medications. EPS include parkinsonism, akathisia, dystonia, and tardive dyskinesia.
EXUDATE.: Fluid that accumulates and penetrates the walls of vessels, leaking into the surrounding tissue.

F

FACIAL ASYMMETRY.: Term used to describe when one side of the face appears different than the other.
FACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY (FSH).: This form of muscular dystrophy, also known as Landouzy-Dejerine condition, begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles of the face, shoulders, and upper arms.
FACTOR VIII.: A protein involved in blood clotting that requires vWF for stability and long-term survival in the bloodstream.
FACTORS.: Coagulation factors are substances in the blood, such as proteins and minerals, that are necessary for clotting. Each clotting substance is designated with roman numerals I through XIII.
FAILURE TO THRIVE.: Significantly reduced or delayed physical growth.
FALLOPIAN TUBE.: Either of a pair of tubes that conduct ova from the ovaries to the uterus.
FAMILIAL.: A trait observed with higher frequency than would be expected by chance within the same family, whether the origin is genetic, environmental, or a combination of both.

FAMILIAL ADENOMATOUS POLYPOSIS (FAP).: Inherited syndrome causing large numbers of polyps and increased risk of colon cancer and other cancers.
FAMILIAL GASTRIC CANCER.: Gastric cancer that occurs at a higher rate in some families.
FANCONI SYNDROME.: A reabsorbtion disorder in the kidney tubules.
FASCICULATIONS.: Involuntary twitching of patient's muscles.
FATTY ACIDS.: The primary component of fats (lipids) in the body. Carnitine palmitoyl transferase (CPT) deficiency involves abnormal metabolism of the longchain variety of fatty acids.
FECAL (OCCULT) BLOOD TEST.: Study of stool (feces) to identify loss of blood in the gastrointestinal system.
FETAL ALCOHOL SYNDROME.: Syndrome characterized by distinct facial features and varying mental retardation in an infant due to impaired brain development resulting from the consumption of alcohol during pregnancy.
FETAL HYDROPS.: A condition in which there is too much fluid in the fetal tissues and/or cavities.
FETOSCOPY.: A technique by which a developing fetus can be viewed directly using a thin, flexible optical device (fetoscope) inserted into the mother's uterus.
FETUS.: The term used to describe a developing human infant from approximately the third month of pregnancy until delivery. The term embryo is used prior to the third month.
FETUS IN FETU.: One fetus growing inside the body of its twin.
FIBRILLATION.: A rapid, irregular heartbeat.
FIBRILLIN.: A protein that is an important part of the structure of the body's connective tissue. In Marfan's syndrome, the gene responsible for fibrillin has mutated, causing the body to produce a defective protein.
FIBRILLIN-2.: A protein that forms part of the body's connective tissue. The precise function of fibrillin-2 is not known.
FIBRIN.: The final substance created through the clotting cascade, which provides a strong, reliable plug to prevent further bleeding from the initial injury.
FIBRINOGEN.: A fibrous protein that circulates in blood and participates in blood clotting by attaching to platelets.
FIBROBLAST.: Cells that form connective tissue fibers like skin.
FIBROBLAST GROWTH FACTOR RECEPTOR GENE.: A type of gene that codes for a cell membrane receptor involved in normal bone growth and development.
FIBROID/FIBROMA.: A non-cancerous tumor of connective tissue made of elongated, threadlike structures, or fibers, which usually grow slowly and are contained within an irregular shape. Fibroids are firm in consistency but may become painful if they start to break down or apply pressure to areas within the body. They frequently occur in the uterus and are generally left alone unless growing rapidly or causing other problems. Surgery is needed to remove fibroids.
FIBROSIS.: The abnormal development of fibrous tissue; scarring.
FINASTERIDE.: An oral medication used to treat male pattern hair loss. Finasteride, sold under the trade names Proscar and Propecia, is an androgen inhibitor.
FINE NEEDLE ASPIRATION (FNA).: Insertion of a thin needle through the skin to an area of sample tissue.
FIRST-DEGREE RELATIVE.: A parent, child or sibling is a first degree relative. First-degree relatives have one half of their genes in common.
FIRST-RANK SYMPTOMS.: A set of symptoms designated by Kurt Schneider in 1959 as the most important diagnostic indicators of schizophrenia. These symptoms include delusions, hallucinations, thought insertion or removal, and thought broadcasting. First-rank symptoms are sometimes referred to as Schneiderian symptoms.
FISH (FLUORESCENCE IN SITU HYBRIDIZATION).: Technique used to detect small deletions or rearrangements in chromosomes by attempting to attach a fluorescent (glowing) piece of a chromosome to a sample of cells obtained from a patient.
FISTULA.: An abnormal passage or communication between two different organs or surfaces.
FLEXION.: The act of bending or condition of being bent.
FLEXION CREASES.: The lines present on the palms of the hands and the soles of the feet from normal bending of these body parts. Some individuals affected with arthrogryposis lack these characteristic lines.
FLUORESCEIN ANGIOGRAPHY.: Procedure to look at the blood vessel system of the eye. Fluorescein, a dye, is injected and photographs are taken as the dye passes through the eye's blood vessels.
FLUOROCHROME.: A fluorescent compound used for visualization in FISH.

FMR-1 GENE.: A gene found on the X chromosome. Its exact purpose is unknown, but it is suspected that the gene plays a role in brain development.
FOCAL SEIZURE.: A seizure that causes a brief and temporary change in movement, sensation, or nerve function.
FOLATE-SENSITIVE FRAGILE SITE.: A chromosome location which, under folate-deficient conditions, appears as a gap in the chromosome and is susceptible to breakage.
FOLLICLE.: A pouch-like depression.
FOLLICLE-STIMULATING HORMONE (FSH).: A hormone that in females stimulates estrogen and in males stimulates sperm production.
FONTANELLE.: One of several "soft spots" on the skull where the developing bones of the skull have yet to fuse.
FORAMEN.: A small opening or hole in a body part or tissue. Dandy-Walker malformation is characterized by the absence or failure to develop the three foramina in the fourth ventricle of the brain.
FOREBRAIN.: The anterior of the front section of the brain.
FOUNDER EFFECT.: increased frequency of a gene mutation in a population that was founded by a small ancestral group of people, at least one of whom was a carrier of the gene mutation.
FRAGILE X SYNDROME.: A condition caused by an abnormality of a region on the X chromosome which may be expressed in males or females, and may increase in severity when inherited from the mother.
FRONTAL BOSSING.: A term used to describe a rounded forehead with a receded hairline.
FRONTAL PLAGIOCEPHALY.: An abnormal condition of the skull in which the front is more developed on one side than it is on the other side.
FUNCTIONAL MAGNETIC RESONANCE IMAGING (FMRI).: A form of imaging of the brain that registers blood flow to functioning areas of the brain.
FUNDUS.: The interior back wall of the eyeball.

G

G-TUBE.: A gastrostomy tube, which is inserted surgically into the stomach and used for feeding and for administering medications.
GAIT.: A manner of walking.
GAIT DISTURBANCES.: Disturbances that affect the manner of walking.
GALACTITOL.: An alcohol derivative of galactose that builds up in the lens and causes cataracts.
GALACTOSE.: One of the two simple sugars, together with glucose, that makes up the protein, lactose, found in milk. Galactose can be toxic in high levels.
GALACTOSEMIA.: Abnormally high levels of galactose in the blood due to an inherited defect in the conversion of galactose to glucose.
GALACTOSURIA.: High levels of galactose found in the urine that is seen with galactosemia.
GALLBLADDER.: A small, pear-shaped organ in the upper right hand corner of the abdomen. It is connected by a series of ducts (tube-like channels) to the liver, pancreas, and duodenum (first part of the small intestine). The gallbladder receives bile from the liver, and concentrates and stores it. After a meal, bile is squeezed out of the gallbladder into the intestine, where it aids in digestion of food.
GAMETE.: A reproductive cell; an ovum or sperm
GAMMA AMINO BUTYRIC ACID (GABA).: An amino acid that functions as the major inhibitory neurotransmitter in the nervous system.
GAMMA KNIFE.: Equipment that precisely delivers a concentrated dose of radiation to a predetermined target using gamma rays.
GANGLIONEUROBLASTOMA.: A tumor of the nerve fibers and ganglion cells.
GANGLIOSIDE.: A fatty (lipid) substance found within the brain and nerve cells.
GANGRENE.: Decay or death of body tissue because the blood supply is cut off. Tissues that have died in this way must be surgically removed.
GASTRIC.: Associated with the stomach.
GASTRIC TUBE.: A tube that is surgically placed though the skin of the abdomen to the stomach so that feeding with nutritional liquid mixtures can be accomplished.
GASTROENTEROLOGIST.: A physician who specializes in disorders of the digestive system.
GASTROESPHAGEAL REFLUX.: The return of the contents of the stomach back up into the esophagus.
GASTROINTESTINAL.: Pertaining to the digestive organs and structures, including the stomach and intestines.

GASTROINTESTINAL (GI) SYSTEM.: The body system involved in digestion, the breaking down and use of food. It includes the stomach, small intestine, and large intestine. Also known as the gastrointestinal tract.
GASTROSCHISIS.: A small defect in the abdominal wall normally located to the right of the umbilicus, and not covered by a membrane, where intestines and other organs may protrude.
GASTROSTOMY.: The construction of an artificial opening from the stomach through the abdominal wall to permit the intake of food.
GAUCHER DISEASE.: Autosomal recessive metabolic disorder caused by dysfunction of the lysosomal enzyme beta-glucosidase.
GAVAGE.: Feeding tube.
GENE.: A building block of inheritance, which contains the instructions for the production of a particular protein, and is made up of a molecular sequence found on a section of DNA. Each gene is found on a precise location on a chromosome.
GENE MUTATION.: A permanent change in genetic material that is transmittable.
GENE THERAPY.: Replacing a defective gene with the normal copy.
GENE TRANSCRIPTION.: The process by which genetic information is copied from DNA to RNA, resulting in a specific protein formation.
GENETIC.: Referring to genes and characteristics inherited from parents.
GENETIC ANTICIPATION.: The tendency for an inherited disease to become more severe in successive generations.
GENETIC COUNSELOR.: A health professional with advanced training in genetics and psychology who educates people about genetic conditions and testing.
GENETIC DISEASE.: A disease that is (partly or completely) the result of the abnormal function or expression of a gene; a disease caused by the inheritance and expression of a genetic mutation.
GENETIC ENGINEERING.: The manipulation of genetic material to produce specific results in an organism.
GENETIC HETEROGENEITY.: The occurrence of the same or similar disease, caused by different genes among different families.
GENETIC SEX.: The gender determined by the sex chromosomes; XX is female, XY is male.
GENETIC SUSCEPTIBILITY.: The predisposition to a disease resulting from one or more genetic traits.
GENETIC TEST.: Testing of chromosomes and genes from an individual or unborn baby for a genetic condition. Genetic testing can only be done if the gene is known.
GENETICIST.: A specialist (MD or PhD) who has training and certification in diagnosing, managing, and counseling individuals/families with genetic disorders. Genetics counselors hold a master's degree in medical genetics, and provide many of the same services as geneticists.
GENETICS.: The study of hereditary traits passed on through the genes.
GENITAL TRACT.: The organs involved in reproduction. In a male, they include the penis, testicles, prostate and various tubular structures to transport seminal fluid and sperm. In a female, they include the clitoris, vagina, cervix, uterus, fallopian tubes and ovaries.
GENITAL.: Refers to the sexual or reproductive organs that are visible outside the body.
GENITAL TRACT.: The organs involved in reproduction. In a male, they include the penis, testicles, prostate, and various tubular structures to transport seminal fluid and sperm. In a female, they include the clitoris, vagina, cervix, uterus, fallopian tubes, and ovaries.
GENITOURINARY.: Related to the reproductive and urinary systems of the body.
GENOME.: All of the DNA in one cell.
GERM-LINE GENE THERAPY.: The introduction of genes into reproductive cells or embryos to correct inherited genetic defects that can cause disease.
GERM LINE MOSAICISM.: A rare event that occurs when one parent carries an altered gene mutation that affects his or her germ line cells (either the egg or sperm cells) but is not found in the somatic (body) cells.
GERMLINE.: The cell line from which gametes arise.
GESTATIONAL AGE.: An estimation of the age of the pregnancy. The beginning of gestation or pregnancy is counted from the first day of the woman's last menstrual period, although conception usually takes place about two weeks later.
GESTATIONAL DIABETES.: Diabetes of pregnancy that can be insulin- or non-insulin-dependent. Usually resolves following delivery, but may predispose to recurrent gestational diabetes and/or other forms of diabetes.
GILLBERG'S CRITERIA.: A six-item checklist for Asperger syndrome developed by Christopher Gillberg, a Swedish researcher. It is widely used as a diagnostic tool.

GINGIVITIS.: Inflammation of the gums of the mouth, characterized by redness, swelling, and a tendency to bleed.
GLAUCOMA.: A common eye disease characterized by increased fluid pressure in the eye that damages the optic nerve, which carries visual impulses to the brain. Glaucoma can be caused by another eye disorder, such as a tumor or congenital malformation, or can appear without obvious cause, but if untreated it generally leads to blindness.
GLIOBLASTOMA MULTIFORME.: Tumor of the central nervous system consisting of undifferentiated glial cells.
GLOBIN.: One of the component protein molecules found in hemoglobin. Normal adult hemoglobin has a pair each of alpha-globin and beta-globin molecules.
GLOBOID CELLS.: Large cells containing excess toxic metabolic "waste" of galactosylceramide and psychosine.
GLOBUS PALLIDUS.: A small paired structure present in the deep portion of the brain, in front of the brainstem, that is considered a part of the basal ganglia and helps in movement control.
GLOMERULI.: Tiny clusters of capillaries in the kidney.
GLOMERULUS.: A structure in the kidney composed of blood vessels that are actively involved in the filtration of the blood.
GLUCOCEREBROSIDE.: A cerebroside that contains glucose in the molecule.
GLUCOSE.: One of the two simple sugars, together with galactose, that makes up the protein, lactose, found in milk. Glucose is the form of sugar that is usable by the body to generate energy.
GLUTEN.: A protein found in wheat, rye, barley, and oats.
GLYCOGEN.: The chemical substance (a macromolecule) used by muscles to store sugars and starches for later use. It is composed of repeating units of glucose.
GLYCOGENESIS.: The metabolic process responsible for the formation of glycogen from many glucose molecules.
GLYCOGENOLYSIS.: The metabolic process responsible for the break down of glycogen to mobilize glucose.
GLYCOLYSIS.: The pathway in which a cell breaks down glucose into energy.
GLYCOPROTEIN.: A protein with at least one carbohydrate group.
GLYCOPROTEIN IIB/IIIA (GP IIB/IIIA).: Sugar-proteins on the surface of platelets that bind to the fibrous protein, fibrinogin. These sugar-proteins are defective in Glanzmann's thrombasthenia.
GLYCOSYLPHOSPHATIDYLINOSITOL (GPI).: A fat that attaches proteins to the outside walls of blood cells.
GOITER.: An enlargement of the thyroid gland, causing tissue swelling that may be seen and/or felt in the front of the neck. May occur in people who have overactive production of thyroid hormones (hyperthyroidism), decreased production of thyroid hormones (hypothyroidism), or among people who have normal production of thyroid hormones.
GONAD.: The organ that will become either a testis (male reproductive organ) or ovary (female reproductive organ) during fetal development.
GONADOTROPHIN.: Hormones that stimulate the ovary and testicles.
GONIOSCOPE.: An instrument used to examine the trabecular meshwork; consists of a magnifier and a lens equipped with mirrors.
GRAFT-VERSUS-HOST DISEASE.: In bone marrow transplantation, the complication that occurs when the donor's cells attack the recipient's tissues, in part due to non-identical donor-recipient HLA types.
GRAND MAL SEIZURE.: A seizure that causes a loss of consciousness, a loss of bladder control, generalized muscle contractions, and tongue biting.
GRANULOCYTOPENIA.: A reduced number of white blood cells in the circulation.
GRAY MATTER.: Areas of the brain and spinal cord that are comprised mostly of unmyelinated nerves.
GREAT TOE.: The first and largest toe on the foot.
GRIEF REACTION.: The normal depression felt after a traumatic major life occurrence such as the loss of a loved one.
GROWTH FACTORS.: Cellular-signaling components that stimulate cell division or other cell processes.
GROWTH HORMONE.: A hormone that eventually stimulates growth. Also called somatotropin.
GUSTATORY LACRIMATION.: Abnormal development of the tear ducts causing tears when chewing.

H

HALLUCAL POLYDACTYLY.: The appearance of an extra great toe.
HALLUCINATION.: A sensory experience of something that does not exist outside the mind. A person can experience a hallucination in any of the five senses. Auditory hallucinations are a common symptom of schizophrenia.
HALLUX.: The great toe.
HAMARTOMA.: An overgrowth of normal tissue.
HAPLOID.: Means "half the number"; refers to a single set of chromosomes, the number in a sperm or egg cell, but half the number in a non-sex cell.
HAPLOINSUFFICIENCY.: The lack of one of the two normal copies of a gene. Haploinsufficiency can result in a genetic disorder if normal function requires both copies of the gene and is one explanation for a dominant pattern of inheritance.
HAPLOTYPE.: A set of alleles that are inherited together as a unit on a single chromosome because of their close proximity.
HEAD TURN.: Habitual head position that has been adopted to compensate for abnormal eye movements.
HEARING THRESHOLD.: The minimum sound level at which a particular individual can hear. This is also called the hearing level (HL) of that person.
HEART VALVE.: One of four structures found within the heart that prevents backwards flow of blood into the previous chamber.
HEIMLICH MANEUVER.: An action designed to expel an obstructing piece of food from the throat. It is performed by placing the fist on the abdomen, underneath the breastbone, grasping the fist with the other hand (from behind), and thrusting it inward and upward.
HELICOBACTER PYLORI (H. PYLORI).: Bacterium that infects humans and may be associated with an increased risk of gastric cancer.
HELLER'S SYNDROME.: Another name for Childhood Disintegrative Disorder (CDD). It is also sometimes called dementia infantilis.
HELPER T-CELL.: Specialized white blood cell that assists in humoral and cellular immunity.
HEMANGIOBLASTOMA.: A tumor of the brain or spinal cord arising in the blood vessels of the meninges or brain.
HEMANGIOMA.: Benign skin tumor made up of clusters of newly formed blood vessels.
HEMATIN.: A drug administered intravenously to halt an acute porphyria attack. It causes heme biosynthesis to decrease, preventing the further accumulation of heme precursors.
HEMATOMA.: An accumulation of blood, often clotted, in a body tissue or organ, usually caused by a break or tear in a blood vessel.
HEMATOPOETIC GROWTH FACTORS.: Substances that assist in the formation of blood cells.
HEMATURIA.: The presence of blood in the urine.
HEME.: The iron-containing molecule in hemoglobin that serves as the site for oxygen binding.
HEMIFACIAL MICROSOMIA.: Term used to describe when one side of the face is smaller than the other.
HEMIHYPERPLASIA.: A condition in which overdevelopment or excessive growth of one half of a specific organ or body part on only one side of the body occurs.
HEMIHYPERTROPHY.: Asymmetric overgrowth in which there is an increase in size of existing cells.
HEMIPLEGIA.: Paralysis of one side of the body.
HEMIVERTEBRA.: A defect in which one side or half of a vertebra fails to form.
HEMIZYGOUS.: Having only one copy of a gene or chromosome.
HEMOCHROMATOSIS.: Accumulation of large amounts of iron in the tissues of the body.
HEMOGLOBIN.: An iron-containing pigment of red blood cells composed of four amino acid chains (alpha, beta, gamma, delta) that delivers oxygen from the lungs to the cells of the body and carries carbon dioxide from the cells to the lungs.
HEMOGLOBIN A.: Normal adult hemoglobin that contains a heme molecule, two alpha-globin molecules, and two beta-globin molecules.
HEMOGLOBIN A1C TEST.: A screening test for diabetes.
HEMOGLOBIN ELECTROPHORESIS.: A laboratory test that separates molecules based on their size, shape, or electrical charge.
HEMOGLOBIN S.: Hemoglobin produced in association with the sickle cell trait; the beta-globin molecules of hemoglobin S are defective.
HEMOLYTIC.: Refers to the type of anemia caused by the breakdown of red blood cells, as opposed to anemia due to decreased production, for example.

HEMOLYTIC ANEMIA.: Anemia that results from premature destruction and decreased numbers of red blood cells.
HEMORRHAGE.: Very severe, massive bleeding that is difficult to control. Hemorrhage can occur in hemophiliacs after what would be a relatively minor injury to a person with normal clotting factors.
HEMOSTASIS.: The arrest of bleeding by blood coagulation.
HEPATIC.: Referring to the liver.
HEPATITIS.: A viral disease characterized by inflammation of the liver cells (hepatocytes). People infected with hepatitis B or hepatitis C virus are at an increased risk for developing liver cancer.
HEPATOMEGALY.: An abnormally large liver.
HEPATOSPLENOMEGALY.: Enlargement of the liver and spleen.
HEREDITARY ANGIONEUROTIC EDEMA.: Abbreviated HANE, or HAE, this is an inherited kind of angioneurotic edema. Type I HANE is caused by a deficiency of C1-INH. Type II HANE is caused by a malformation of the C1-INH protein.
HEREDITARY NON-POLYPOSIS COLON CANCER (HNPCC).: A genetic syndrome causing increased cancer risks, most notably colon cancer; also called Lynch syndrome.
HERITABILITY.: The proportion of causative factors for a disease that can be attributed to genetics.
HERMANSKY-PUDLAK SYNDROME (HPS).: A rare form of albinism, most common in the Puerto Rican community, which can cause pigment changes, lung disease, intestinal disorders, and blood disorders.
HERNIA.: A rupture in the wall of a body cavity, through which an organ may protrude.
HETEROCHROMIA IRIDES.: A medical term for individuals with different-colored eyes.
HETEROGENEOUS.: A set of symptoms or a disorder caused by several different gene mutations.
HETEROPLASMY.: When all copies of mitochondrial DNA are not the same, and a mix of normal and mutated mitochondrial DNA is present.
HETEROTAXY.: Random organ positioning in an individual that can result in multiple malformations with severe heart defects, livers found in the middle of the body, spleen abnormalities, and intestines turned in the opposite direction from normal (gastrointestinal malrotation).
HETEROTOPIA.: Small nodules of gray matter that are present outside the cortex.
HETEROZYGOTE/HETEROZYGOUS.: Having two different versions of the same gene.
HETEROZYGOUS.: Having two different versions of the same gene.
HIGH-FUNCTIONING AUTISM (HFA).: A subcategory of autistic disorder consisting of children diagnosed with IQs of 70 or higher.
HIGH DENSITY LIPOPROTEIN (HDL).: A cholesterol carrying substance that helps remove cholesterol from the cells of the body and deliver it to the liver where it is digested and removed from the body.
HIGHLY AEROBIC TISSUES.: Tissue that requires the greatest amount of oxygen to thrive.
HIRSCHPRUNG DISEASE.: A deformation in which the colon becomes enlarged (megacolon), caused by abnormal nerve control of that portion of the large intestine.
HIRSUITISM.: The presence of coarse hair on the face, chest, upper back, or abdomen in a female as a result of excessive androgen production.
HISTAMINE.: A substance released by immune system cells in response to presence of allergen; stimulates widening of blood vessels and increased porousness of blood vessel walls so that fluid and protein leak out from blood to surrounding tissue, causing inflammation of local tissues.
HISTOLOGIC.: Pertaining to histology, the study of cells and tissues at the microscopic level.
HISTOLOGICAL STUDIES.: Laboratory tests performed on tissue samples and cells.
"HITCHHIKER" THUMBS.: A congenital anomaly of the thumb in which it is abnormally positioned at a right angle to the first joint.
HLA-B27.: Stands for a specific form of human leukocyte antigen, the proteins involved in immune system function. Strongly associated with ankylosing spondylitis.
HLA TYPE.: Refers to the unique set of proteins called human leukocyte antigens. These proteins are present on each individual's cell and allow the immune system to recognize "self" from "foreign." HLA type is particularly important in organ and tissue transplantation.
HMLH1 AND HMSH2.: Genes known to control mismatch repair of genes.
HOLOPROSENCEPHALY.: A malformation of the brain in which the two hemispheres or lobes of the brain do not separate properly.

HOLT-ORAM SYNDROME.: Inherited disorder characterized by congenital heart defects and abnormalities of the arms and hands; may be associated with Duane retraction syndrome.
HOMEOPATHIC.: A holistic and natural approach to healthcare.
HOMEOSTASIS.: A state of physiological balance.
HOMEOTIC GENES.: Developmental control genes active in the embryo.
HOMOCYSTEINE.: An amino acid that is not used to produce proteins in the human body.
HOMOGENTISATE 1,2-DIOXYGENASE (HGD).: Homogentisic acid oxidase, the fourth enzyme in the metabolic pathway for the breakdown of phenylalanine.
HOMOGENTISIC ACID (HGA).: 2,5-Dihydroxyphenylacetic acid, the third intermediate in the metabolic pathway for the breakdown of phenylalanine.
HOMOLOGOUS CHROMOSOMES.: Homologous chromosomes are two chromosomes of a doublet set that are identical, particularly for the genes that are on them.
HOMOLOGUES.: Chromosomes or chromosome parts identical with respect to their construction and genetic content (i.e. the two chromosome #1s are homologous, as are the two #2s, #3s, etc…).
HOMOPLASMY.: When all copies of mitochondrial DNA are the same, or have the same mutation.
HOMOZYGOTE/HOMOZYGOUS.: Having two identical copies of a gene or chromosome.
HOMOZYGOUS.: Having two identical copies of a gene or chromosome.
HORMONE.: A chemical messenger produced by the body that is involved in regulating specific bodily functions such as growth, development, and reproduction.
HORMONE THERAPY.: Treatment of cancer by changing the hormonal environment, such as testosterone and estrogen.
HUMAN GENOME PROJECT.: An international effort begun in 1990 to locate and identify the 100,000 genes on the 46 human chromosomes.
HUMAN LEUKOCYTE ANTIGENS (HLA).: Proteins that help the immune system function, in part by helping it to distinguish cells that are part of the body from those that come from outside.
HUMORAL IMMUNITY.: A type of acquired immunity mediated by B-cells and their secreted antibodies; important in fighting bacterial and some viral infections.
HUNTINGTON'S DISEASE.: A rare hereditary disease that causes progressive chorea (jerky muscle movements) and mental deterioration that ends in dementia. Huntington's symptoms usually appear in patients in their 40s. Also called Huntington's chorea and Huntington disease.
HYALINE.: A clear substance that occurs in cell deterioration.
HYDRAMNIOS.: A condition in which there is too much amniotic fluid in the womb during pregnancy.
HYDRANENCEPHALY.: Congenital enlargement of the head and brain.
HYDROCEPHALUS.: An abnormal accumulation of cerebrospinal fluid within the brain. This accumulation can be harmful by pressing on brain structures and damaging them.
HYDROLASE.: Enzyme that uses water to break down substances.
HYDROMETROCOLPOS.: An abnormal accumulation of fluids in the uterus and vagina.
HYDRONEPHROSIS.: Obstruction of the tube that carries urine from the kidney into the bladder causing the pelvis and kidney duct to become swollen with excess urine.
HYDROPS FETALIS.: A condition characterized of massive edema in a fetus or newborn.
HYDROXYAPATITE.: A mineral that gives bone its rigid structure and strength. It is primarily composed of calcium and phosphate.
HYDROXYUREA.: A drug that has been shown to induce production of fetal hemoglobin. Fetal hemoglobin has a pair of gamma-globin molecules in place of the typical beta-globins of adult hemoglobin. Higher-than-normal levels of fetal hemoglobin can ameliorate some of the symptoms of thalassemia.
HYPERAMMONEMIA.: An excess of ammonia in the blood.
HYPERCALCEMIA.: High levels of calcium in the blood.
HYPEREXTENSIBILITY.: The ability to extend a joint beyond the normal range.
HYPERHIDROSIS.: Excessive perspiration that may be either general or localized to a specific area.
HYPERKERATOSIS.: Thickening of the skin.
HYPERLORDOSIS.: An exaggerated curve in the lower (lumbar) portion of the back.

HYPERMOBILITY.: Unusual flexibility of the joints, allowing them to be bent or moved beyond their normal range of motion.
HYPEROSTOSIS.: Overgrowth of the bone.
HYPERPHAGIA.: Over-eating.
HYPERPIGMENTATION.: An abnormal condition characterized by an excess of melanin in localized areas of the skin, which produces areas that are much darker than the surrounding unaffected skin.
HYPERSENSITIVE.: A process or reaction that occurs at above normal levels; overreaction to a stimulus.
HYPERTELORISM.: A wider-than-normal space between the eyes.
HYPERTHERMIA.: Body temperature that is much higher than normal (i.e., higher than 98.6°F).
HYPERTONIA.: Excessive muscle tone or tension, causing resistance of muscle to being stretched.
HYPERTRICHOSIS.: Growth of hair in excess of the normal. Also called hirsutism.
HYPERTROPHIC CARDIOMYOPATHY.: A condition in which the muscle of the heart is abnormally excessively thickened. In microscopic examination, normal alignment of muscle cells is absent (myocardial disarray).
HYPERTROPHY.: Increase in the size of a tissue or organ brought on by the enlargement of its cells rather than cell multiplication.
HYPNAGOGIC HALLUCINATIONS.: Dream-like auditory or visual hallucinations that occur while falling asleep.
HYPOCHONDROPLASIA.: An autosomal dominant form of dwarfism whose physical features are similar to those of achondroplasia but milder. Affected individuals have mild short stature and a normal facial appearance.
HYPOGLYCEMIA.: An abnormally low glucose (blood sugar) concentration in the blood.
HYPOGONADISM.: Small testes in men and scarse or irregular mentruation for females.
HYPOHIDROSIS.: Insufficient perspiration or absent perspiration which may be either general or localized to a specific area.
HYPOKETOSIS.: Decreased levels of ketone bodies.
HYPOMYELINATION.: The death of myelin on a nerve or nerves.
HYPOPHOSPHATEMIA.: The state of having abnormally low levels of phosphate in the bloodstream.
HYPOPIGMENTATION.: Decreased or absent color (pigment) in a tissue.
HYPOPLASIA.: An underdeveloped or incomplete tissue or organ usually due to a decrease in the number of cells.
HYPOSPADIAS.: A congenital abnormality of the penis in which the urethral opening is located on the underside of the penis rather than at its tip.
HYPOTHALAMUS.: A part of the forebrain that controls heartbeat, body temperature, thirst, hunger, body temperature and pressure, blood sugar levels, and other functions.
HYPOTHYROID.: Deficiency in thyroid gland activity or thyroid hormone levels.
HYPOTONIA.: Reduced or diminished muscle tone or strength.

I

IATROGENIC.: Caused by (-genic) doctor (iatro-). An iatrogenic condition is a condition that is caused by the diagnosis or treatment administered by medical professionals. Iatrogenic conditions may be caused by any number of things, including: unsterile medical instruments or devices, contaminated blood or implantations, or contaminated air within the medical facility.
ICHTHYOSIS.: A group of congenital skin disorders of keratinization characterized by dryness and scaling of the skin.
IDIOPATHIC.: Refers to a disease or condition of unknown origin.
IGE.: An antibody composed of protein; specific forms of IgE produced by cells of immune system in response to different antigens that contact the body; major factor that stimulates the allergic response.
ILIAC ARTERIES.: Arteries that supply blood to the lower body including the pelvis and legs.
IMMUNE SYSTEM.: A major system of the body that produces specialized cells and substances that interact with and destroy foreign antigens that invade the body.
IMMUNODEFICIENCY.: A defect in the immune system, leaving an individual vulnerable to infection.
IMMUNOGLOBULIN.: A protein molecule formed by mature B cells in response to foreign proteins in the body; the building blocks for antibodies.
IMMUNOLOGIC.: Related to immunology, the study of how the body's immune system fights disease. Many immunologic disorders are characterized by the body's use of antibodies.

IMMUNOTHERAPY.: Treatment of cancer by stimulating the body's immune defense system.
IMPAIRED GLUCOSE TOLERANCE (IGT).: May be a precursor to diabetes; marked by blood glucose levels that are not quite elevated to the level seen in nephrogenic diabetes insipidus.
IMPERFORATE ANUS.: Also known as anal atresia. A birth defect in which the opening of the anus is absent or obstructed.
IMPOTENCE.: The inability to have a penile erection, which can be due to tissue damage resulting from sickling within the penis (priapism).
IMPRINTING.: Process that silences a gene or group of genes. The genes are silenced depending on if they are inherited through the egg or the sperm.
IN UTERO.: While in the uterus; before birth.
IN VITRO FERTILIZATION.: A process by which a woman's eggs are surgically removed and fertilized in the laboratory. It is then possible to transfer the developing embryos to her uterus to achieve a pregnancy; this is not always successful, however.
INCLUSION BODY.: Abnormal storage compartment inside a cell.
INCOMPLETE PENETRANCE.: Absence of disease in an individual known to carry the gene for that disease.
INDUCTION.: Process where one tissue (the prechordal plate, for example) changes another tissue (for example, changes tissue into neural tissue).
INFANTILE SPASMS.: The form of grand mal or focal seizures experienced by infants prior to the development of many voluntary muscular controls.
INFECTIVE ENDOCARDITIS.: An infection of the endothelium, the tissue lining the walls of the heart.
INFERIOR OLIVARY NUCLEUS.: A small collection of cells seen in the lower part of the brainstem, which has connections to the cerebellum and is involved in control of movements.
INFERTILE.: Incapable of reproduction.
INFERTILITY.: Inability in a woman to become pregnant.
INFLAMMATION.: Pain, redness, swelling, and heat that develop in response to tissue irritation or injury. It is usually caused by the immune system's response to the the body's contact with a foreign substance, such as an allergen or pathogen.
INFORMED CONSENT.: Provision of complete information to a competent individual regarding a treatment or test. Part of informed consent is to ensure a patient's understanding of the pros and cons of a procedure and to get their voluntary authorization to perform the procedure.
INGUINAL HERNIA.: A condition in which part of the intestines protrudes through a tear in the muscles of the abdomen.
INHERITANCE PATTERN.: The way in which a genetic disease is passed on in a family.
INHERITED GIANT PLATELET DISORDER (IGPD).: A group of hereditary conditions that cause abnormal blood clotting and other conditions.
INSOMNIA.: An inability to either fall or stay asleep, particularly at a time of day when sleep is expected. A number of medications are available, and may be used, for treatment.
INSULIN-DEPENDENT DIABETES MELLITUS (IDDM).: Synonymous with type I diabetes, the more serious form of diabetes that tends to affect people at a younger age.
INSULIN-LIKE GROWTH FACTOR I.: A hormone released by the liver in response to high levels of growth hormone in the blood. This growth factor is very similar to insulin in chemical composition; and, like insulin, it is able to cause cell growth by causing cells to undergo mitosis (cell division).
INSULIN.: A hormone produced by the pancreas that is secreted into the bloodstream and regulates blood sugar levels.
INSULIN RECEPTOR GENE.: The gene responsible for the production of insulin receptor sites on cell surfaces. Without properly functioning insulin receptor sites, cells cannot attach insulin from the blood for cellular use.
INSULIN RESISTANCE.: An inability to respond normally to insulin in the bloodstream.
INTERPERSONAL THERAPIES.: Also called "talking therapy," this type of psychological counseling is focused on determining how dysfunctional interpersonal relationships of the affected individual may be causing or influencing symptoms of depression.
INTRACRANIAL HEMORRHAGE.: Abnormal bleeding within the space of the skull and brain.
INTRACRANIAL PRESSURE.: The pressure of the fluid between the brain and skull.
INTRAGENIC.: Occuring within a single gene.
INTRAUTERINE.: Situated or occurring in the uterus.

INTRAUTERINE GROWTH RETARDATION.: A form of growth retardation occurring in the womb that is not caused by premature birth or a shorten gestation time. Individuals affected with this condition are of lower than normal birth weight and lower than normal length after a complete gestation period.
INTRAVENOUS.: A route for administration of fluids, nutrients, blood products, or medications. A small, flexible plastic tube is inserted into a vein by way of a needle to establish this route.
INTRAVENOUS PYELOGRAM.: An x-ray assessment of kidney function.
INTRON.: That portion of the DNA sequence of a gene that is not directly involved in the formation of the chemical that the gene codes for.
INTUSSUSCEPTION.: One piece of bowel inside another, causing obstruction.
INVERSION.: A type of chromosomal defect in which a broken segment of a chromosome attaches to the same chromosome, but in reverse position.
ION CHANNEL.: Cell membrane proteins that control the movement of ions into and out of the cell.
IONIZING RADIATION.: High-energy radiation such as that produced by x rays.
IQ.: Abbreviation for Intelligence Quotient. Compares an individual's mental age to his/her true or chronological age and multiplies that ratio by 100.
IRIS.: The circular membrane that forms the colored portion of the eye and expands or contracts around the pupil.
IRON OVERLOAD.: A side effect of frequent blood transfusions in which the body accumulates abnormally high levels of iron. Iron deposits can form in organs, particularly the heart, and cause life-threatening damage.
ISCHEMIC.: Refers to ischemia, a decrease in the blood supply to an area of the body caused by obstruction or constriction of blood vessels.
ISCHOPAGUS.: Conjoined twins who are attached at the lower half of the body.
ISOCHROMOSOME.: A chromosome is normally composed of two sections referred to as p and q; instead, an isochromosome is an abnormal chromosome made up of two p sections or two q sections.
ISOMERISM.: Refers to the organs that typically come in pairs, but where the right organ is structurally different from the left organ, but in a condition, like asplenia, the organs are identical.
ISOMERS.: Two chemicals identical in chemical composition (contain the same atoms in the same amounts) that have differing structures. The normal prion protein and the infectious prion protein are conformational isomers of one another. They have the same chemical structures, but for some reason, assume different shapes.
ISOTOPE.: Any of two or more species of atoms of a chemical element with the same atomic number and nearly identical chemical behavior but with differing atomic mass and physical properties.
ISOZYME/ISOENZYME.: A group of enzymes that perform the same function, but are different from one another in their structure or how they move.

J

JAUNDICE.: A condition in which the skin and whites of the eyes take on a yellowish color due to an increase of bilirubin (a compound produced by the liver) in the blood. Also called icterus.
JOINT CONTRACTURES.: Stiffness of the joints that prevents full extension.
JOINT DISLOCATION.: The displacement of a bone from its socket or normal position.

K

KABUKI.: Traditional Japanese popular drama performed with highly stylized singing, dancing, makeup, and clothing. Kabuki syndrome (also known as Niikawa-Kuroki syndrome) gets its name from the characteristic long eyelid fissures with eversion of the lower eyelids that is similar to the makeup worn by Kabuki actors.
KALLIKREIN.: A protein necessary for the activation of chemicals that cause dilation of blood vessels to allow increased blood flow to an area that requires more blood than normal. It is also capable of cleaving the complement, C5, into C5a, a much more robust and active form of this complement molecule.
KANNER'S SYNDROME.: Another name for autism.
KARYOTYPE.: A standard arrangement of photographic or computer-generated images of chromosome pairs from a cell in ascending numerical order, from largest to smallest.
KARYOTYPING.: A laboratory test used to study an individual's chromosome make-up. Chromosomes are separated from cells, stained, and arranged in order from largest to smallest so that their number and structure can be studied under a microscope.

KERATIN.: A tough, non-water-soluble protein found in the nails, hair, and the outermost layer of skin. Human hair is made up largely of keratin.
KERATINOCYTES.: Skin cells.
KERATOACANTHOMA.: A firm nodule on the skin typically found in areas of sun exposure.
KERATOLYTIC.: An agent that dissolves or breaks down the outer layer of skin (keratins).
KERATOSIS.: A raised thickening of the outer horny layer of the skin.
KETOACIDOSIS.: A condition that results when organic compounds (such as propionic acid, ketones, and fatty acids) build up in the blood and urine.
KETOLACTIC ACIDOSIS.: The overproduction of ketones and lactic acid.
KETONE BODIES.: Products of fatty acid metabolism in the liver that can be used by the brain and muscles as an energy source.
KETONES.: Poisonous acidic chemicals produced by the body when fat instead of glucose is burned for energy. Breakdown of fat occurs when not enough insulin is present to channel glucose into body cells.
KETONURIA.: The presence of excess ketone bodies (organic carbohydrate-related compounds) in the urine.
KETOSIS.: An abnormal build-up of chemicals called ketones in the blood. This condition usually indicatea a problem with blood sugar regulation.
KIDNEY.: Either of two organs in the lumbar region that filter the blood, excreting the end products of the body's metabolism in the form of urine and regulating the concentrations of hydrogen, sodium, potassium, phosphate and other ions in the body.
KIDNEY TUBULES.: A portion of the kidneys that causes water to be excreted as urine or reabsorbed into the body.
KLINEFELTER SYNDROME.: A syndrome that occurs in XXY males; characterized by sterility and small testes; normal intelligence.
KNOCKOUT EXPERIMENT.: A type of genetic experiment in which researchers are able to deactivate, or knock out, a gene that may influence a particular trait, such as vulnerability to alcohol.
KYPHOSCOLIOSIS.: Abnormal front-to-back and side-to-side curvature of the spine.
KYPHOSIS.: An abnormal outward curvature of the spine, with a hump at the upper back.

L

L-CARNITINE.: A substance made in the body that carries wastes from the body's cells into the urine.
LABIA.: The two parts (lips) of the vulva, the external female genitalia.
LACRIMAL DUCTS.: Tear ducts.
LACTIC ACID.: The major by-product of anaerobic (without oxygen) metabolism.
LACTIC ACIDOSIS.: A condition characterized by the accumulation of lactic acid in bodily tissues. The cells of the body make lactic acid when they use sugar as energy. If too much of this acid is produced, the person starts feeling ill with symptoms such as stomach pain, vomiting, and rapid breathing.
LACTOSE.: A sugar made up of of glucose and galactose. It is the primary sugar in milk.
LAPAROSCOPY.: A diagnostic procedure in which a small incision is made in the abdomen and a slender, hollow, lighted instrument is passed through it. The doctor can view the ovaries more closely through the laparoscope, and if necessary, obtain tissue samples for biopsy.
LAPAROTOMY.: An operation in which the abdominal cavity is opened up.
LARYNX.: Also known as the voice box, the larynx is the part of the airway that lies between the pharynx and the trachea. It is composed of cartilage that contains the apparatus for voice production–the vocal cords and the muscles and ligaments that move the cords.
LASER-ASSISTED IN-SITU KERATOMILEUSIS (LASIK).: A procedure that uses a cutting tool and a laser to modify the cornea and correct moderate to high levels of myopia.
LATERAL RECTUS MUSCLE.: The muscle that turns the eye outward toward the ear (abduction).
LEBERS HEREDITARY OPTIC ATROPHY OR LEBERS HEREDITARY OPTIC NEUROPATHY (LHON).: Discovered in 1871 by Theodore Leber, the painless loss of central vision in both eyes, usually occurring in the second or third decade of life, caused by a mutation in mitochondrial DNA. Other neurological problems such as tremors or loss of ankle reflexes, may also be present.
LEFT-RIGHT AXIS.: The developmental feature in a fetus that determines which side of the body is left and which side is right; it conducts the location and positioning of the fetus' internal organs.

LEFT VENTRICLE.: Portion of the heart from which blood is pumped into the system.
LEFT VENTRICULAR ENLARGEMENT.: Abnormal enlargement of the left lower chamber of the heart.
LENS.: The transparent, elastic, curved structure behind the iris (colored part of the eye) that helps focus light on the retina.
LENTIGENE.: A dark colored spot on the skin.
LEPROSY.: A chronic, contagious skin and nervous system disease that leads, in the more serious form, to numbness, muscle weakness, and paralysis. Leprosy is sometimes referred to as Hansen's disease.
LEPTOMENINGEAL ANGIOMA.: A swelling of the tissue or membrane surrounding the brain and spinal cord, which can enlarge with time.
LESION.: A defective or injured section or region of the brain (or other body organ).
LEUCOPENIA.: A decrease in white blood cells.
LEUKEMIA.: Cancer of the blood forming organs which results in an overproduction of white blood cells.
LEUKOCYTE.: A white blood cell. The neutrophils are a type of leukocyte.
LEUKOCYTOSIS.: An increase in the number of leukocytes in the blood.
LEUKODYSTROPHY.: A disease that affects the white matter called myelin in the CNS.
LEUKOENCEPHALOPATHY.: Any of various diseases, including leukodystrophies, affecting the brain's white matter.
LEVOTHYROXINE.: A form of thyroxine (T4) for replacement of thyroid hormones in hypothryoidism.
LEWY BODIES.: Areas of injury found on damaged nerve cells in certain parts of the brain associated with dementia.
LI-FRAUMENI SYNDROME.: Inherited syndrome known to cause increased risk of different cancers, most notably sarcomas.
LIFETIME RISK.: A risk which exists over a person's lifetime; a lifetime risk to develop disease means that the chance is present until the time of death.
LIGAMENT.: A type of connective tissue that connects bones or cartilage and provides support and strength to joints.
LIMB GIRDLE.: Area around the shoulders and hips.
LIMB-GIRDLE MUSCULAR DYSTROPHY (LGMD).: Form of muscular dystrophy that begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles around the hips and shoulders.
LIMB DYSTONIA.: Involuntary cramp or spasm that affects the hands. Also known as writer's cramp.
LIMITED SCLERODERMA.: A subtype of systemic scleroderma with limited skin involvement. It is somestimes called the CREST form of scleroderma, after the initials of its five major symptoms.
LINKAGE.: The association between separate DNA sequences (genes) located on the same chromosome.
LINKAGE ANALYSIS.: A method of finding mutations based on their proximity to previously identified genetic landmarks.
LIPASE.: A digestive enzyme found in pancreatic fluid that breaks down fats.
LIPID.: Large, complex biomolecule, such as a fatty acid, that will not dissolve in water. A major constituent of membranes.
LIPOMA.: A benign tumor composed of well-differentiated fat cells.
LIPOPIGMENTS.: Substances made up of fats and proteins found in the body's tissues.
LIPOPROTEIN.: A lipid and protein chemically bound together, which aids in transfer of the lipid in and out of cells, across the wall of the intestine, and through the blood stream.
LIPOSOME.: Fat molecule made up of layers of lipids.
LISSENCEPHALY.: A condition in which the brain has a smooth appearance because the normal convolutions (gyri) failed to develop.
LOCALIZED SCLERODERMA.: Thickening of the skin from overproduction of collagen.
LOCUS.: A specific physical location on a DNA molecule.
LONG BONES.: The femur in the leg and the humerus in the arm.
LONGITUDINAL STUDY.: A type of research project in which the same subjects are interviewed repeatedly at intervals over a period of time.
LORDOSIS.: An abnormal curvature of the spine in which the lumbar, or lower section, is excessively curved.

LORDOSIS.: An exaggeration of the normal lumbar curve such that the chest is prominent and the small of the back is hollowed.
LORICIN.: One of the proteins that give skin cells its structure.
LOW DENSITY LIPOPROTEINS (LDL).: A cholesterol carrying substance that can remain in the blood stream for a long period of time.
LUMBAR LORDOSIS.: Abnormal inward curvature of the spine.
LUPUS ERYTHEMATOSUS.: A chronic inflammatory disease that affects many tissues and parts of the body including the skin.
LUTENIZING HORMONE (LH).: A hormone secreted by the pituitary gland that regulates the menstrual cycle and triggers ovulation in females. In males it stimulates the testes to produce testosterone.
LYMPH NODE.: A bean-sized mass of tissue that is part of the immune system and is found in different areas of the body.
LYMPHATIC SYSTEM.: Lymph nodes and lympatic vessels that transport infection fighting cells to the body.
LYMPHEDEMA DISTICHIASIS.: Autosomal dominant condition with abnormal or absent lymph vessels. Common signs include a double row of eyelashes (distichiasis) and edema of the limbs beginning around puberty.
LYMPHOCYTES.: Also called white blood cells, lymphocytes mature in the bone marrow to form B cells, which fight infection.
LYMPHOMA.: A malignant tumor of the lymph nodes.
LYMPHOSCINTIGRAPHY.: Procedure that helps to look at the lymph nodes in the body. Requires an injection of radioactive material to help see the lymph nodes and lymphatic system.
LYNCH SYNDROME.: A genetic syndrome causing increased cancer risks, most notably colon cancer. Also called hereditary non-polyposis colon cancer (HNPCC).
LYSINE.: A crystalline basic amino acid essential to nutrition.
LYSIS.: Area of destruction.
LYSOSOMAL.: Pertaining to the lysosomes, special parts (organelles) of cells that contain a number of enzymes important in the breakdown of large molecules such as proteins and fats.
LYSOSOMAL STORAGE DISEASE.: A category of disorders that includes mannosidosis.
LYSOSOME.: Membrane-enclosed compartment in cells, containing many hydrolytic enzymes; where large molecules and cellular components are broken down.

M

MACROCEPHALY.: A head that is larger than normal.
MACROGLOSSIA.: A large tongue.
MACROMOLECULES.: A large molecule composed of thousands of atoms.
MACROPHAGE.: Specialized white blood cells that play a role in breaking down old or abnormal red blood cells.
MACROSOMIA.: Overall large size due to overgrowth.
MACROSTOMIA.: A mouth that is larger or wider than normal.
MACULA.: A small spot located in the back of the eye that provides central vision and allows people to see colors and fine visual details.
MACULAR DEGENERATION.: Progressive condition that affects the macula, a small portion of the retina at the back of the eye.
MACULE.: A flat, discolored spot or patch on the skin.
MADAROSIS.: The medical term for loss of hair from the eyebrows or eyelashes. Madarosis may be associated with a form of alopecia areata called alopecia totalis. It may also result from such diseases as leprosy and syphilis, or from trauma.
MADELUNG'S DEFORMITY.: A forearm-bone malformation characterize by a short forearm, arced or bowshaped radius, and dislocation of the ulna.
MAFFUCCI DISEASE.: A manifestation of Ollier's disease (multiple enchondromatosis) with hemangiomas, which present as soft tissue masses.
MAGNETIC RESONANCE IMAGING (MRI).: An imaging technique that uses a large circular magnet and radio waves to generate signals from atoms in the body. These signals are used to construct detailed images of internal body structures and organs, including the brain.
MAJOR DEPRESSION.: A psychological condition in which the sufferer experiences one or more disabling attacks of depression that lasts two or more weeks.
MAJOR HISTOCOMPATIBILITY COMPLEX (MHC).: Includes HLA, as well as other components of the immune system. Helps the immune system function, in part by helping it to distinguish "self" from "non-self."

MALAR HYPOLPLASIA.: Small or underdeveloped cheekbones.
MALAR HYPOPLASIA.: Small or underdeveloped cheekbones.
MALE-LETHAL X-LINKED DOMINANCE.: An inheritance pattern in which affected male children die from the characteristics of the trait. This death is typically either embryonic, fetal, or neonatal.
MALFORMATION.: An abnormality in an organ or body structure caused by a dysfunctional developmental process.
MALIGNANT.: A tumor growth that spreads to another part of the body, usually cancerous.
MALIGNANT HYPERTHERMIA.: A condition brought on by anesthesia during surgery.
MALROTATION.: An abnormality that occurs during the normal rotation of an organ or organ system.
MAMMOGRAM.: A procedure in which both breasts are compressed/flattened and exposed to low doses of x rays, in an attempt to visualize the inner breast tissue.
MAMMOGRAPHY.: X rays of the breasts; used to screen for breast cancer.
MANDIBLE.: Lower jaw bone.
MANDIBULAR HYPOPLASIA.: Underdevelopment of the jaw.
MANNOSE.: A type of sugar that forms long chains in the body.
MANOMETRY.: A balloon study of internal anal sphincter pressure and relaxation.
MAO-B INHIBITORS.: Inhibitors of the enzyme monoamine oxidase B. MAO-B helps break down dopamine; inhibiting it prolongs the action of dopamine in the brain. Selegiline is an MAO-B inhibitor.
MAORI.: A native New Zealand ethnic group.
MARFANOID.: Term for body type which is similar to people with Marfan syndrome. Characterized by tall, lean body with long arms and long fingers.
MARFANOID HABITUS.: An abnormally low weight to height ratio that is sometimes seen in extremely tall and thin people.
MASCULINIZATION.: Development of excess body and facial hair, deepening of the voice, and increase in muscle bulk in a female due to a hormone disorder.
MASSETER SPASM.: Stiffening of the jaw muscles. Often one of the first symptoms of malignant hyperthermia susceptibility that occurs after exposure to a trigger drug.
MATERNAL.: Relating to the mother.
MATERNAL SERUM SCREENING.: A blood test offered to pregnant women usually under the age of 35, which measures analytes in the mother's blood that are present only during pregnancy, to screen for Down syndrome, trisomy 18, and neural tube defects.
MATERNAL UNIPARENTAL DISOMY.: Chromosome abnormality in which both chromosomes in a pair are inherited from one's mother.
MATURITY-ONSET DIABETES OF THE YOUNG (MODY).: A rare form of diabetes inherited in an autosomal dominant fashion. It is similar to type II diabetes, but develops before the age of 25.
MAXILLA.: The bone of the upper jaw which serves as a foundation of the face and supports the orbits.
MAXILLARY HYPOPLASIA.: Underdevelopment of the upper jaw.
MECONIUM.: The first waste products to be discharged from the body in a newborn infant, usually greenish in color and consisting of mucus, bile and so forth.
MEDIAL RECTUS MUSCLE.: The muscle that turns the eye inward toward the nose (adduction).
MEDIUM CHAIN ACYL-COA DEHYDROGENASE.: Abbreviated MCAD, this is the enzyme responsible for the breakdown of medium chain fatty acids in humans. People affected with MCAD deficiency produce a form of MCAD that is not as efficient as the normal form of MCAD.
MEDIUM CHAIN FATTY ACIDS.: Fatty acids containing between four and 14 carbon atoms.
MEDULLARY CAVITY.: The marrow-filled cavity inside of a long bone (such as the femur).
MEDULLOBLASTOMA.: Tumor of the central nervous system derived from undifferentiated cells of the primitive medullary tube.
MEGACOLON.: Dilation of the colon.
MEIOSIS.: The process in which a cell in the testes or ovaries undergoes chromosome separation and cell division to produce sperms or eggs.
MELANIN.: A pigment that creates hair, skin, and eye color. Melanin also protects the body by absorbing ultraviolet light.
MELANOCYTES.: A cell that can produce melanin.
MELANOMA.: Tumor, usually of the skin.
MELANOSOMES.: Granules of pigment within melanocytes that synthesize melanin.

MELATONIN.: A sleep-inducing hormone secreted by the pineal gland.
MEMORY CELLS.: B-cells whose antibodies recognized antigens from a previous infection; able to mount a quick, efficient response upon a second infection by the same organism.
MENDEL, GREGOR.: Austrian monk who discovered the basic principals of hereditary.
MENDELIAN GENETICS.: A set of parameters describing the traditional method of the transmission of genes from one generation to the next.
MENINGES.: The two-layered membrane that covers the brain and spinal cord.
MENINGITIS.: An infection of the covering of the brain.
MENOPAUSE.: The end of a woman's reproductive years, signaled by the end of her menstrual periods.
MENSTRUATION.: Discharge of blood and fragments of the uterine wall from the vagina in a monthly cycle in the absence of pregnancy.
MENTAL RETARDATION.: Significant impairment in intellectual function and adaptation in society. Usually associated an intelligence quotient (IQ) below 70.
MERMAID SYNDROME.: Alternate name for sirenomelia, often used in older references.
MESOMELIA.: Shortness of the portion of arm connecting the elbow to the wrist or forearm.
MESOMELIC.: The anatomical term used to describe the middle of a limb. The bones that constitute the middle of the arm are the radius and ulna, and mesomelic bones of the leg are the tibia and fibula.
MESONEPHRIC DUCT.: Embryonic structure that in the male becomes the vas deferens, and in both sexes gives rise to the ureters leading to the kidney.
METABOLIC ACIDOSIS.: High acidity (low pH) in the body due to abnormal metabolism, excessive acid intake, or retention in the kidneys.
METABOLIC DISORDER.: A disorder that affcets the metabolism of the body.
METABOLIC MYOPATHIES.: A broad group of muscle diseases whose cause is a metabolic disturbance of some type.
METABOLIC PATHWAY.: A sequence of chemical reactions that lead from some precursor to a product, where the product of each step in the series is the starting material for the next step.
METABOLISM.: The total combination of all of the chemical processes that occur within cells and tissues of a living body.
METACARPAL.: A hand bone extending from the wrist to a finger or thumb.
METACENTRIC.: When a chromosome has the centromere in the middle of the chromosome it is called a metacentric chromosome.
METACHRONOUS.: Occurring at separate time intervals.
METAFEMALE.: An out of date term for XXX females, also called triple X syndrome.
METAPHYSEAL FLARING.: A characteristic found only by x rays. If present, it means that the ends of the bone are wider than normal.
METAPHYSIS.: The growth zone of long bones located between the diaphysis (shaft) and epiphysis (end).
METASTASIS.: The spreading of cancer from the original site to other locations in the body.
METASTATIC CANCER.: A cancer that has spread to an organ or tissue from a primary cancer located elsewhere in the body.
METATARSAL.: A foot bone extending from the ankle to a toe.
METHYLATION TESTING.: DNA testing that detects if a gene is active, or if it is imprinted.
METHYLMALONIC ACID.: An intermediate product formed when certain substances are broken down in order to create usable energy for the body.
METHYLMALONIC COA MUTASE (MCM).: The enzyme responsible for converting methylmalonic acid to succinic acid, in the pathway to convert certain substances to usable energy.
METHYLMALONICACIDEMIA.: The buildup of high levels of methylmalonic acid in the bloodstream due to an inborn defect in an enzyme.
MICRO-DELETION SYNDROME.: A collection of signs and symptoms caused by a deletion of a gene or genes that is too small to be seen through the microscope.
MICROARRAY.: An ordered arrangement of many different genes on a glass slide or silicon chip. Microarrays allow researchers to study large numbers of genes simultaneously in determining different levels of gene activity in such complex processes as the body's response to alcohol.
MICROCEPHALIC.: Having an abnormally small head.

MICROCEPHALIC PRIMORDIAL DWARFISM SYNDROMES.: A group of disorders characterized by profound growth delay and small head size.
MICROCEPHALY.: An abnormally small head.
MICROCORNEA.: Abnormal smallness of the cornea.
MICROCYTIC, HYPOCHROMIC ANEMIA.: An anemia marked by deficient hemoglobin and small red blood cells.
MICRODELETION SYNDROME.: A syndrome caused by the deletion of a very small amount of chromosomal material.
MICRODONTIA.: Small teeth.
MICROGNATHIA.: A term used to describe small, underdeveloped lower jaw and chin.
MICROGNATHY.: Having a very small and receding jaw.
MICROMELIA.: The state of having extremely short limbs.
MICROPHTHALMIA.: Small or underdeveloped eyes.
MICROTIA.: Small or underdeveloped ears.
MIDLINE DEFECTS.: Defects involving organs along the center of the body such as the lips, penis, and corpus callosum.
MIDLINE ORGANS.: Organs found along the center of the body such as the lips, penis, and corpus callosum.
MINIATURIZATION.: The process of shortening and thinning of the hair shafts that is found in androgenetic alopecia. It is caused by the effects of DHT on the hair follicle.
MINOXIDIL.: A topical medication sold under the trade name Rogaine for the treatment of male pattern hair loss. It is applied to the scalp as a 2% or 5% solution.
MISCARRIAGE.: Spontaneous pregnancy loss.
MISMATCH REPAIR.: Repair of gene alterations due to mismatching.
MITOCHONDRIA.: Spherical or rod-shaped structures of the cell. Mitochondria contain genetic material (DNA and RNA) and are responsible for converting food to energy.
MITOCHONDRIAL INHERITANCE.: Inheritance associated with the mitochondrial genome, which is inherited exclusively from the mother.
MITOCHONDRIAL MYOPATHIES.: Diseases of the muscle accompanied by abnormal changes in the cell mitochondria and which result in excessive accumulation of lipids.
MITOSIS.: The process by which a somatic cell—a cell not destined to become a sperm or egg—duplicates its chromosomes and divides to produce two new cells.
MITRAL VALVE.: The heart valve that prevents blood from flowing backwards from the left ventricle into the left atrium. Also known as bicuspid valve.
MITRAL VALVE PROLAPSE.: A heart defect in which one of the valves of the heart (which normally controls blood flow) becomes floppy. Mitral valve prolapse may be detected as a heart murmur but there are usually no symptoms.
MIXED-TYPE HEARING LOSS.: Hearing loss that involves both conductive and sensorineural losses.
MOLECULAR ANALYSIS.: Evaluation of molecules, tests that may identify single gene mutations.
MONOSOMY.: Missing an entire copy of a chromosome or a piece of one copy of a chromosome.
MONOZYGOTIC.: From one zygote, as in identical twins. The zygote is the first cell formed by the union of sperm and egg.
MORPHEA.: The most common form of localized scleroderma.
MORPHOGENESIS.: The normal developmental process of the body's structure and form.
MOSAIC.: A term referring to a genetic situation in which an individual's cells do not have the exact same composition of chromosomes. In Down syndrome, this may mean that some of the individual's cells have a normal 46 chromosomes, while other cells have an abnormal 47 chromosomes.
MOSAICISM.: A genetic condition resulting from a mutation, crossing over, or nondisjunction of chromosomes during cell division, causing a variation in the number of chromosomes in the cells.
MOTOR FUNCTION.: The ability to produce body movement by complex interaction of the brain, nerves, and muscles.
MOTOR NEURONS.: Class of neurons that specifically control and stimulate voluntary muscles.
MOTOR SKILLS DISORDER.: A disorder that affects motor coordination or its development, and the control of particular groups of muscles that perform activities.
MOTOR UNITS.: Functional connection with a single motor neuron and muscle.

MOTTLED RETINA.: Changes in the retina of the eye causing a loss of visual acuity.
MUCOCILIARY ESCALATOR.: The coordinated action of tiny projections on the surfaces of cells lining the respiratory tract, which moves mucus up and out of the lungs.
MUCOLIPID.: Lipid that accumulate in cells in mucolipidosis disorders.
MUCOLIPIN-1.: Protein in the cell membrane, probably a calcium ion channel, involved in recycling membrane lipids and is deficient in mucolipidosis IV.
MUCOLYTIC.: An agent that dissolves or destroys mucin, the chief component of mucus.
MUCOPOLYSACCHARIDE.: A complex molecule made of smaller sugar molecules strung together to form a chain. Found in mucous secretions and intercellular spaces.
MUCOPOLYSACCHARIDOSIS I H (MPS I H)..: Another name for Hurler syndrome.
MUCORMYCOSIS.: An organism that commonly infects individuals with diabetes following ketosis events.
MUCOUS MEMBRANE.: Thin, mucous covered layer of tissue that lines organs such as the intestinal tract.
MULLERIAN DUCTS.: Structures in the embryo that, in females, develop into the fallopian tubes, the uterus, the cervix, and the upper vagina; in males they disappear except for the vestigial vagina masculina and the appendix testis.
MULTI-INFARCT DEMENTIA.: Dementia caused by damage to brain tissue resulting from a series of blood clots or clogs in the blood vessels. It is also called vascular dementia.
MULTIFACTORIAL.: Describes a disease that is the product of the interaction of multiple genetic and environmental factors.
MULTIFACTORIAL INHERITANCE.: A type of inheritance pattern where many factors, both genetic and environmental, contribute to the cause.
MULTIFOCAL BREAST CANCER.: Multiple primary cancers in the same breast.
MULTIPLE CARBOXYLASE DEFICIENCY.: A type of propionic acidemia characterized by an inability to metabolize biotin.
MULTIPLE SCLEROSIS (MS).: A progressive, autoimmune disease of the central nervous system characterized by damage to the myelin sheath that covers nerves. The disease, which causes progressive paralysis, is marked by periods of exacerbation and remission.
MULTIPLEX ASSAY.: A procedure that allows the testing of several gene samples simultaneously.
MURMUR.: A noise, heard with the aid of a stethoscope, made by abnormal patterns of blood flow within the heart or blood vessels.
MUSCULAR DYSTROPHY.: A group of inherited diseases characterized by progressive wasting of the muscles.
MUTAGEN.: An environmental influence that causes changes in DNA.
MUTANT.: A change in the genetic material that may alter a trait or characteristic of an individual or manifest as disease.
MUTATION.: A permanent change in the genetic material that may alter a trait or characteristic of an individual, or manifest as disease; a mutation can be transmitted to offspring.
MYELIN.: A substance rich in protein and fatty substances that forms layers around (sheaths) nerve fibers, insulating and helping nerves transmit electrochemical messages between the brain and the rest of the body.
MYELODYSPLASIA.: A bone marrow disorder that can develop into aplastic anemia requiring bone marrow or stem cell transplantation.
MYELOMENINGOCELE.: A sac that protrudes through an abnormal opening in the spinal column.
MYOCLONUS.: Twitching or spasms of a muscle or an interrelated group of muscles.
MYOGLOBINURIA.: The abnormal presence of myoglobin, a product of muscle disintegration, in the urine. Results in dark-colored urine.
MYOPATHY.: Any abnormal condition or disese of muscle tissue, characterized by muscle weakness and wasting.
MYOPIA.: Nearsightedness, a vision problem in which distant objects appear blurry. Myopia results when the cornea is too steep or the eye is too long and the light doesn't focus properly on the retina.
MYOTONIA.: The inability to normally relax a muscle after contracting or tightening it.
MYOTONIC DYSTROPHY.: A form of muscular dystrophy, also known as Steinert's condition, characterized by delay in the ability to relax muscles after forceful contraction, wasting of muscles, as well as other abnormalities.

MYOTUBULE.: An intermediate stage in muscle fiber development, where the fiber is tubular with a centrally placed nucleus, instead of a peripheral eccentric nucleus.
MYXEDEMA.: Swelling of the face, hands, feet, and genitals due to hypothyroidism.
MYXOID.: Resembling mucus.

N

N-ACETYLGLUCOSAMINE-1-PHOSPHOTRANSFERASE (GNPTA).: Enzyme that attaches a signal to other enzymes and directs those enzymes to the lysosome; deficient in mucolipidoses II and III.
NALTREXONE.: A medication originally developed to treat addiction to heroin or morphine that is also used to treat alcoholism. It works by reducing the craving for alcohol rather than by producing vomiting or other unpleasant reactions.
NANISM.: Short stature.
NARCOTICS.: Strong, prescription medication that can be effective in treating pain, but have the potential to be habit-forming if their use is not supervised correctly.
NASOGASTRIC TUBE.: A long flexible tube inserted through the nasal passageways, down the throat, and into the stomach. Used to drain the contents of the stomach.
NATURAL IMMUNITY.: First line immune response that is non-specific. Includes action of phagocytes, natural killer cells, and complement cells.
NATURAL KILLER CELLS.: Specialized white blood cells involved in natural immunity. Can kill some viruses and cancer cells.
NECROSIS.: Death of a portion of tissue differentially affected by disease or injury.
NECROTIZING ENCEPHALOMYELOPATHY.: A progressive degeneration of the brain and central nervous system. This condition leads to the deaths of nearly all individuals affected with type A pyruvate carboxylase deficiency.
NEGATIVE SYMPTOMS.: Symptoms of schizophrenia characterized by the absence or elimination of certain behaviors. DSM-IV specifies three negative symptoms: affective flattening, poverty of speech, and loss of will or initiative.
NEONATAL.: Neonatal refers to the first 28 days after birth.
NEONATE.: A newborn infant up to six weeks of age.
NEONATOLOGIST.: A physician (pediatrician) who has special training in the care of newborns (neonates).
NEPHRON.: The basic functional unit of the kidney, a nephron is a mciroscopic tube that filters the blood that flows into the kidney and produces urine.
NEPHROPATHY.: Kidney disease.
NEPHROSIS.: A non-inflammatory disease of the kidneys.
NERVE CONDUCTION.: A test that measures the speed of conduction of electrical impulses through nerves using a series of electrical shocks delivered through electrodes placed on the skin surface.
NERVE CONDUCTION TESTING.: Procedure that measures the speed at which impulses move through the nerves.
NERVOUS SYSTEM.: The complete network of nerves, sense organs, and brain in the body.
NEUCHAL TRANSLUCENCY.: A pocket of fluid at the back of an embryo's neck visible via ultrasound that, when thickened, may indicate the infant will be born with a congenital heart defect.
NEURAL.: Pertaining to a nerve, the nervous system, or any tissue with nerves, including the brain and the spinal cord.
NEURAL CREST CELLS.: A group of cells in the early embryo, located on either side of the area that will eventually develop into the spinal cord. The cells migrate (move) away from the area and give rise to various body structures, including melanocytes (pigment producing cells), certain structures of the face and head, and parts of the nervous system.
NEURAL FOLDS AND TUBE.: Portions of the developing embryo from which the brain and spinal cord arise.
NEURAL TUBE DEFECT.: A group of congential disorders in which the brain and spinal cord are malformed and lack the protective skeletal and soft tissue encasement.
NEUROCRISTOPATHY.: A disorder that results from abnormal development and/or migration of the neural crest cells in the embryo.
NEURODEGENERATIVE.: Relating to degeneration of nerve tissues.
NEUROFIBROMA.: A soft tumor usually located on a nerve.
NEUROFIBROMATOSIS.: Progressive genetic condition often including multiple café-au-lait spots, multiple raised nodules on the skin known as neurofibromas, developmental delays, slightly larger head sizes, and freckling of the armpits, groin area, and iris.

NEUROLEPTIC.: Another name for the older type of antipsychotic medications given to schizophrenic patients.
NEUROLOGIC.: Relating to the brain and central nervous system.
NEUROLOGIST.: A physician who specializes in disorders of the nervous system, including the brain, spine, and nerves.
NEUROMETABOLIC DISORDER.: Any disorder or condition that affects both the central nervous system (CNS) and the metabolism of the body.
NEUROMUSCULAR.: Involving both the muscles and the nerves that control them.
NEUROMUSCULAR JUNCTION.: The site at which nerve impulses are transmitted to muscles.
NEURON.: The fundamental nerve cell that conducts impulses across the cell membrane.
NEURONAL CEROID LIPOFUSCINOSES.: A family of four progressive neurological disorders.
NEUROPATHY.: A disease or abnormality of the peripheral nerves (the nerves outside the brain and spinal cord). Major symptoms include weakness, numbness, paralysis, or pain in the affected area.
NEUROPROTECTIVE.: Conveying some form of protection to the nervous system from injury.
NEUROTRANSMITTER.: Chemical in the brain that transmits information from one nerve cell to another.
NEUTROPENIA.: A condition in which the number of leukocytes (a type of white or colorless blood cell) is abnormally low, mainly in neutrophils (a type of blood cell).
NEUTROPHIL.: The primary type of white blood cell involved in inflammation. Neutrophils are a type of granulocyte, also known as a polymorphonuclear leukocyte.
NEVUS.: Any anomaly of the skin present at birth, including moles and various types of birthmarks. The plural form is nevi.
NEVUS FLAMMEUS.: A flat blood vessel tumor present at birth, also known as a "port wine stain."
NEWBORN SCREENING.: The act of testing all infants for a specific disease shortly after birth for the purpose of preventing disease progression through prompt medical treatment.
NITRATES/NITRITES.: Chemical compounds found in certain foods and water that, when consumed, may increase the risk of gastric cancer.
NITROGEN.: A gaseous element that makes up the base pairs in DNA.
NON-INSULIN-DEPENDENT DIABETES MELLITUS (NIDDM).: Synonymous with type II diabetes, the most common form of diabetes that tends to be highly influenced by lifestyle factors and typically occurs in adulthood.
NON-SYNDROMIC HEARING LOSS.: Hearing loss that is not accompanied by other symptoms characteristic of a larger genetic syndrome.
NONDISJUNCTION.: Non-separation of a chromosome pair, during either meiosis or mitosis.
NONSPHEROCYTIC.: Literally means not sphere-shaped. Refers to the shape of red blood cells in nonspherocytic hemolytic anemia.
NONSYNDROMIC HEARING LOSS.: Hearing loss that is not accompanied by other symptoms characteristic of a larger genetic syndrome.
NONVERBAL LEARNING DISABILITY (NLD).: A learning disability syndrome identified in 1989 that may overlap with some of the symptoms of Asperger syndrome.
NOONAN SYNDROME.: A genetic syndrome that possesses some characteristics similar to cardiofaciocutanoue syndrome. It is unclear whether the two syndrome are different or two manifestations of the same disorder.
NUCLEAR INHERITANCE.: Inheritance associated with the nuclear genome (the 23 pairs of chromosomes). This inheritance follows the rules of segregation developed by Gregor Mendel and is alternately termed Mendelian inheritance.
NUCLEAR ISOLATE.: An isolated preparation of the contents of the nucleus of a cell, which contains the DNA.
NUCLEIC ACID.: A type of chemical used as a component for building DNA. The nucleic acids found in DNA are adenine, thymine, guanine, and cytosine.
NUCLEOTIDE.: One of the molecules that form the building blocks of DNA or RNA. The nucleotides of DNA include a phosphate group, four chemical bases (adenine, cytosine, guanine, and thymine), and a sugar containing five carbon atoms. In RNA the thymine base is replaced by uracil.
NUCLEUS.: The central part of a cell that contains most of its genetic material, including chromosomes and DNA.

NYSTAGMUS.: Involuntary, rhythmic movement of the eye.

O

OBLIGATE CARRIER.: An individual who, based on pedigree analysis, must carry a genetic mutation for a particular genetic disease. Parents of a child with an autosomal recessive disorder are obligate carriers.
OBSESSIVE COMPULSIVE DISORDER (OCD).: Disorder characterized by persistent, intrusive, and senseless thoughts (obsessions) or compulsions to perform repetitive behaviors that interfere with normal functioning.
OCCIPITAL LOBE.: An anatomical subdivision, located at the back of the brain, that contains the visual cortex.
OCHRONOSIS.: A condition marked by pigment deposits in cartilage, ligaments, and tendons.
OCULAR.: A broad term that refers to structure and function of the eye.
OCULAR ALBINISM.: A type of albinism that affects the vision.
OCULO-DIGITAL REFLEX.: A reflex causing an individual to press on their eyes with their fingers or fists.
OCULO.: Related to the eye.
OCULOCUTANEOUS ALBINISM.: Inherited loss of pigment in the skin, eyes, and hair.
OCULOMOTOR NERVE.: Cranial nerve III; the nerve that extends from the midbrain to several of the muscles that control eye movement.
OCULOPHARYNGEAL MUSCULAR DYSTROPHY (OPMD).: Form of muscular dystrophy affecting adults of both sexes, and causing weakness in the eye muscles and throat.
OKIHIRO SYNDROME.: Inherited disorder characterized by abnormalities of the hands and arms and hearing loss; may be associated with Duane retraction syndrome.
OLIGODACTYLY.: The absence of one or more fingers or toes.
OLIGODONITA.: The absence of one or more teeth.
OLIGOHYDRAMNIOS.: Reduced amount of amniotic fluid. Causes include non-functioning kidneys and premature rupture of membranes. Without amniotic fluid to breathe, a baby will have underdeveloped and immature lungs.
OLIGOSACCHARIDE.: Several monosaccharide (sugar) groups joined by glycosidic bonds.
OLLIER DISEASE.: Also termed multiple enchondromatosis. Excessive cartilage growth within the bone extremities that result in benign cartilaginous tumors arising in the bone cavity.
OMPHALOCELE.: A birth defect where the bowel and sometimes the liver, protrudes through an opening in the baby's abdomen near the umbilical cord.
OMPHALOPAGUS.: Conjoined twins who are attached at the abdomen.
ONYCHOGRYPHOSIS.: Overgrowth of the fingernails and toenails.
OPHTHALMOLOGIST.: A physician specializing in the medical and surgical treatment of eye disorders.
OPHTHALMOLOGY.: The medical specialty of vision and the eye.
OPHTHALMOSCOPE.: An instrument, with special lighting, designed to view structures in the back of the eye.
OPISTHOTONOS.: An arched position of the body in which only the head and feet touch the floor or bed when the patient is lying on their back.
OPTIC DISC.: The small area in the retina where the optic nerve enters the eye; it is not sensitive to light and is therefore called "the blind spot."
OPTIC NERVE.: A bundle of nerve fibers that carries visual messages from the retina in the form of electrical signals to the brain.
OPTOMETRIST.: A medical professional who examines and tests the eyes for disease and treats visual disorders by prescribing corrective lenses and/or vision therapy. In many states, optometrists are licensed to use diagnostic and therapeutic drugs to treat certain ocular diseases.
ORAL LOADING TEST.: A procedure in which cystine is administered orally to a patient and plasma levels of cystine are measured. Under normal circumstances, amino acids are absorbed by the intestine and result in an increase in plasma amino acid levels. However, in cystinuria, there is a defect in the absorption process and blood levels of amino acids do not rise or rise slowly after eating.
ORBITAL CYSTS.: Small fluid-filled sacs that abnormally develop inside the bony cavity of the skull that holds the eyeball.
ORGANELLE.: Small, sub-cellular structures that carry out different functions necessary for cellular survival and proper cellular functioning.

ORGANIC ACIDURIA.: The condition of having organic acid in the urine.
ORTHODONTIST.: Dentist who specializes in the correction of misaligned teeth.
ORTHOKERATOLOGY.: A method of reshaping the cornea using a contact lens. It is not considered a permanent method to reduce myopia.
ORTHOPEDIC.: Pertaining to the field of orthopedics, the science of the bones and diseases of the bones.
ORTHOPEDIST.: A doctor specializing in treatment of the skeletal system and its associated muscles and joints.
ORTHOSTATIC.: Posture that is maintained while standing.
ORTHOSTATIC HYPOTENSION.: A sudden decrease in blood pressure upon sitting up or standing. May be a side effect of several types of drugs.
OSMOLARITY.: The concentration of an osmotic solution, especially when measured in osmols or milliosmols per liter of solution.
OSMOTICALLY.: Referring to the movement of a solvent through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.
OSSICLES.: Any of the three bones of the middle ear, including the malleus, incus, and stapes.
OSSIFICATION.: The process of the formation of bone from its precursor, a cartilage matrix.
OSTEOARTHRITIS.: A noninflammatory type of arthritis, usually occurring in older people, characterized by degeneration of cartilage, enlargement of the margins of the bones, and changes in the membranes in the joints. Also called degenerative arthritis.
OSTEOBLASTS.: A bone cell that makes bone.
OSTEOCHONDROMATOSIS.: Another name for hereditary multiple exostoses, meaning a growth of bone and cartilage.
OSTEOCLASTS.: A bone cell that breaks down and reabsorbs bone.
OSTEOMA.: A benign bone tumor.
OSTEOMALACIA.: The adult form of rickets, a lack of proper mineralization of bone.
OSTEOPENIA.: Abnormal bone mineralization, usually resulting from a failure of the rate of bone matrix formation to compensate for the rate of bone decomposition.
OSTEOPENIC.: Bone density that is somewhat low, but not osteoporotic.
OSTEOPOROSIS.: Loss of bone density that can increase the risk of fractures.
OTITIS MEDIA.: Inflammation of the middle ear, often due to fluid accumulation secondary to an infection.
OTOLARYNGOLOGIST.: Physician who specializes in the care of the ear, nose, and throat and their associated structures.
OTOSCLEROSIS.: The main type of non-syndromic progressive conductive hearing loss seen in humans. In very advanced cases, otosclerosis can become of mixed type.
OVA.: Another name for the egg cells that are located in the ovaries.
OVARY.: The female reproductive organ that produces the reproductive cell (ovum) and female hormones.
OVULATION.: The monthly process by which an ovarian follicle or cyst ruptures, releasing a mature egg cell.
OXYGENATED BLOOD.: Blood carrying oxygen through the body.
OXYTOCIN.: A hormone that stimulates the uterus to contract during child birth and the breasts to release milk.

P

PACHYDERMA.: An abnormal skin condition in which excess skin is produced that appears similar to that of an elephant (pachyderm).
PACHYGYRIA.: The presence of a few broad gyri (folds) and shallow sulci (grooves) in the cerebral cortex.
PALATE.: The roof of the mouth.
PALLIATIVE.: Treatment done for relief of symptoms rather than a cure.
PALMAR.: Referring to the palms of the hand.
PALMOPLANTAR KERATODERMA.: Group of mostly hereditary disorders characterized by thickening of the corneous layer of skin (hyperkeratosis) on the palms and soles as a result of excessive keratin formation (protein in the skin, hair and nails).
PALMOPLANTAR KERATOSIS.: A raised thickening of the outer horney layer of the skin on the palms of the hand and the soles of the feet.

PALPEBRAL FISSURES.: The opening between the upper and lower eyelids.
PALPITATION.: An irregular heartbeat.
PALSY.: Uncontrolable tremors.
PANCREAS.: An organ located in the abdomen that secretes pancreatic juices for digestion and hormones for maintaining blood sugar levels.
PANCREATIC INSUFFICIENCY.: Reduction or absence of pancreatic secretions into the digestive system due to scarring and blockage of the pancreatic duct.
PANCREATIC ISLET CELL.: Cells located in the pancreas that serve to make certain types of hormones.
PANCREATITIS.: Inflammation of the pancreas.
PANCYTOPENIA.: An abnormal reduction in the number of erythrocytes (red blood cells), leukocytes (a type of white or colorless blood cell), and blood platelets (a type of cell that aids in blood clotting) in the blood.
PANHYPOPITUITARISM.: Generalized decrease of all of the anterior pituitary hormones.
PAPILLOMA.: Any benign localized growth of the skin and the linings of the respiratory and digestive tracts. The most common papilloma is the wart.
PAPILLOMATOUS PAPULES.: Skin-colored, raised bumps (not warts) found on the skin. Most of these growths are benign (non-cancerous) and rarely become malignant (cancerous).
PARAPAGUS.: Conjoined twins who are joined at the side of their lower bodies
PARAPARESIS.: Weakness of the legs without complete paralysis.
PARAPLEGIA.: Loss of voluntary movement and sensation of both lower extremities.
PARASITIC TWINS.: Occurs when one smaller, malformed twin is dependent on the larger, stronger twin for survival.
PARASYMPATHETIC GANGLION CELL.: Type of nerve cell normally found in the wall of the colon.
PARATHYROID GLANDS.: A pair of glands adjacent to the thyroid gland that primarily regulate blood calcium levels.
PARESTHESIA.: An abnormal sensation often described as burning, tickling, tingling, or "pins and needles."
PARKINSON'S DISEASE.: A slowly progressive disease that destroys nerve cells in the basal ganglia and thus causes loss of dopamine, a chemical that aids in transmission of nerve signals (neurotransmitter). Parkinson's is characterized by shaking in resting muscles, a stooping posture, slurred speech, muscular stiffness, and weakness.
PARKINSONISM.: A set of symptoms originally associated with Parkinson disease that can occur as side effects of neuroleptic medications. The symptoms include trembling of the fingers or hands, a shuffling gait, and tight or rigid muscles.
PATAU SYNDROME.: A syndrome caused by trisomy 13; characterized by cleft palate, severe mental retardation, and many other physical defects; usually lethal by age 1.
PATELLA.: The kneecap.
PATENT DUCTUS ARTERIOSUS (PDA).: A congenital anomaly of the heart occurring when the ductus arteriosus (the temporary fetal blood vessel that connects the aorta and the pulmonary artery) does not close at birth.
PATERNAL.: Relating to one's father.
PATHOLOGIST.: A physician who specializes in the diagnosis of disease by looking at living tissues with a microscope.
PECTORALIS MUSCLES.: Major muscles of the chest wall.
PECTUS CARINATUM.: An abnormality of the chest in which the sternum (breastbone) is pushed outward. It is sometimes called "pigeon breast."
PECTUS EXCAVATUM.: An abnormality of the chest in which the sternum (breastbone) sinks inward; sometimes called "funnel chest."
PEDIGREE ANALYSIS.: Analysis of a family tree, or pedigree, in an attempt to identify the possible inheritance pattern of a trait seen in this family.
PELVIC EXAMINATION.: Physical examination performed by a physician, often associated with a Pap smear. The physician inserts his/her finger into a woman's vagina, attempting to feel the ovaries directly.
PENDRIN.: A protein encoded by the PDS (Pendred syndrome) gene located on chromosome 7q31. Pendrin protein is believed to transport iodide and chloride within the thyroid and the inner ear.
PENETRANCE.: The degree to which individuals possessing a particular genetic mutation express the trait that this mutation causes. One hundred percent penetrance is expected to be observed in truly dominant traits.
PEPTIC ULCER.: A wound in the bowel that can be caused by stomach acid or a bacterium called Helicobacter pylori.

PEPTIDE.: A molecular compound made of two or more amino acids.
PERCHLORATE DISCHARGE TEST.: A test used to check for Pendred syndrome by measuring the amount of iodine stored inside the thyroid gland. Individuals with Pendred syndrome usually have more iodine stored than normal, and thus their thyroid will release a large amount of iodine into the bloodstream when they are exposed to a chemical called perchlorate.
PERICARDIAL CAVITY.: Space occupied by the heart.
PERICARDITIS.: Inflammation of the pericardium, the membrane surrounding the heart.
PERINATOLOGIST.: A physician (obstetrician) who has special training in managing difficult pregnancies. Some prenatal tests, such as chorionic villus sampling and level II ultrasound, are performed primarily by perinatologists.
PERIOD OF SUSCEPTIBILITY.: The time when teratogens can cause harm to the developing fetus.
PERIODONTITIS.: Inflammatory reaction of the tissues surrounding and supporting the teeth that can progress to bone destruction and abscess formation, and eventual tooth loss.
PERIOSTEAL.: Relating to the periosteum, which is the connective tissue that covers all human bones.
PERIPHERAL NERVES.: Nerves throughout the body that carry information to and from the spinal cord.
PERIPHERAL NEUROPATHY.: Any disease of the nerves outside of the spinal cord, usually resulting in weakness and/or numbness.
PERIPHERAL VISION.: The ability to see objects that are not located directly in front of the eye. Peripheral vision allows people to see objects located on the side or edge of their field of vision.
PERITONITIS.: Inflammation of the peritoneum, the membrane surrounding the abdominal contents.
PERNICIOUS ANEMIA.: A blood condition with decreased numbers of red blood cells related to poor vitamin B12 absorption.
PEROXISOME.: A cellular organelle containing different enzymes responsible for the breakdown of waste or other products.
PERVASIVE DEVELOPMENTAL DISORDER (PDD).: The term used by the American Psychiatric Association for individuals who meet some but not all of the criteria for autism.
PES PLANUS.: Flat feet.
PEUTZ-JEGHERS SYNDROME.: Inherited syndrome causing polyps of the digestive tract and spots on the mouth as well as increased risk of cancer.
PHAGOCYTE.: White blood cells capable of engulfing and destroying foreign antigen or organisms in the fluids of the body.
PHALANGES.: Long bones of the fingers and toes, divided by cartilage around the knuckles.
PHALILALIA.: Involuntary echoing of the last word, phrase, sentence, or sound vocalized by oneself.
PHENOTYPE.: The physical expression of an individual's genes.
PHENYLALANINE.: An essential amino acid that must be obtained from food since the human body cannot manufacture it.
PHENYLKETORNURIA (PKU).: An inborn error of metabolism that causes buildup of the amino acid, phenylalanine, in the body. The first disease to be used for newborn screening.
PHEOCHROMOCYTOMA.: A small vascular tumor of the inner region of the adrenal gland. The tumor causes uncontrolled and irregular secretion of certain hormones.
PHILTRUM.: The vertical groove at the center of the upper lip.
PHLEBOTOMY.: Drawing blood from a patient's vein as part of diagnosis or therapy. Phlebotomy is sometimes called venesection.
PHOBIA.: An exaggerated fear.
PHOSPHATE.: A substance composed of the elements phosphorus and oxygen that contributes to the hydroxyapatite crystals found in normal bones.
PHOSPHORYLATION.: The addition of phosphoric acid to another compound.
PHOTOPHOBIA.: An extreme sensitivity to light.
PHOTORECEPTORS.: Specialized cells, rods and cones, lining the innermost layer of the eye that convert light into electrochemical impulses; rod cells allow for peripheral and night vision, and cone cells are responsible for perceiving color and for central vision.
PHOTOREFRACTIVE KERATECTOMY (PRK).: A procedure that uses an excimer laser to make modifications to the cornea and permanently correct myopia. As of early 1998, only two lasers have been approved by the FDA for this purpose.
PHYTANIC ACID.: A substance found in various foods that, if allowed to accumulate, is toxic to various tissues. It is metabolized in the peroxisome by phytanic acid hydroxylase.

PHYTANIC ACID HYDROXYLASE.: A peroxisomal enzyme responsible for processing phytanic acid. It is defective in Refsum disease.
PICK'S DISEASE.: A rare type of primary dementia that affects the frontal lobes of the brain. It is characterized by a progressive loss of social skills, language, and memory, leading to personality changes and sometimes loss of moral judgment.
PITUITARY GLAND.: The most important of the endocrine glands (glands that release hormones directly into the bloodstream), the pituitary is located at the base of the brain. Sometimes referred to as the "master gland," it regulates and controls the activities of other endocrine glands and many body processes including growth and reproductive function. Also called the hypophysis.
PLACENTA.: The organ that provides oxygen and nutrition from the mother to the unborn baby during pregnancy. The placenta is attached to the wall of the uterus and leads to the unborn baby via the umbilical cord.
PLANTAR.: Referring to the sole of the foot.
PLAQUES.: Abnormally deposited proteins that interfere with normal cell growth and functioning and usually progresses to cell death.
PLASMA.: The liquid part of the blood and lymphatic fluid that contains antibodies and other proteins.
PLASMA CELLS.: Antibody-secreting B-cells.
PLASMALOGENS.: Fat molecules that are important components of cells and of the myelin sheath that protects nerve cells.
PLASMAPHERESIS.: A procedure in which the fluid component of blood is removed from the bloodstream and sometimes replaced with other fluids or plasma.
PLASMIN.: The blood protein responsible for dissolving blood clots.
PLATELET.: A cell-like particle in the blood that plays an important role in blood clotting. Platelets are activated when an injury causes a blood vessel to break. They change shape from round to spiny, "sticking" to the broken vessel wall and to each other to begin the clotting process. In addition to physically plugging breaks in blood vessel walls, platelets also release chemicals that promote clotting.
PLEURAL CAVITY.: Area of the chest occupied by the lungs.
PLEURITIS.: Inflammation of the pleura, the membrane surrounding the lungs.
PNEUMONIA.: An infection of the lungs.
PODIATRIST.: A physician who specializes in disorders of the feet.
POIKILODERMA.: A condition characterized by skin atrophy, widening of the small blood vessels (telangiectasia), and pigment changes giving a mottled appearance.
POLYDACTYLY.: The presence of extra fingers or toes.
POLYGENIC.: A trait, characteristic, condition, etc. that depends on the activity of more than one gene for its emergence or expression.
POLYHYDRAMNIOS.: A condition in which there is too much fluid around the fetus in the amniotic sac.
POLYMER.: A very large molecule, formed from many smaller, identical molecules.
POLYMERASE CHAIN REACTION (PCR).: A laboratory process used to make a large number of copies of specific genetic information from small amounts of DNA.
POLYMORPHIC.: Describes a gene for which there exist multiple forms, or alleles.
POLYMORPHISM.: A change in the base pair sequence of DNA that may or may not be associated with a disease.
POLYMYOSITIS.: An inflammation of many muscles.
POLYP.: A mass of tissue bulging out from the normal surface of a mucous membrane.
POLYPECTOMY.: Surgical removal of polyps.
POLYPLOIDY.: A condition in which a cell receives more than two complete sets of chromosomes.
POLYPOSIS.: A descriptive term indicating that hundreds to thousands of polyps have developed in an organ.
POLYSACCHARIDE.: Linear or branched macromolecule composed of numerous monosaccharide (sugar) units linked by glycosidic bonds.
POLYSYNDACTYLY.: Having both extra digits (toes, fingers) as well as webbing (syndactyly) between the digits.
POOR MUSCLE TONE.: Muscles that are weak and floppy.
PORENCEPHALY.: A congenital anomaly of the brain in which there are abnormal holes or cavities in the brain.

PORPHYRIN.: A large molecule shaped like a four-leaf clover. Combined with an iron atom, it forms a heme molecule.
PORT-WINE STAIN.: Dark-red birthmarks seen on the skin, named after the color of the dessert wine.
POSER CRITERIA.: Criteria proposed in 1983 as an update to the Schumacher criteria for diagnosing MS; developed to aid neurologists in determining the existence of lesions and other para-clinical evidence of MS.
POSITIONAL CLONING.: Cloning a gene simply on the basis of its position in the genome, without having any idea of the function of the gene.
POSITIVE PREDICTIVE VALUE (PPV).: The probability that a person with a positive test result has, or will get, the disease.
POSITIVE SYMPTOMS.: Symptoms of schizophrenia that are characterized by the production or presence of behaviors that are grossly abnormal or excessive, including hallucinations and thought-process disorder. DSMIV subdivides positive symptoms into psychotic and disorganized.
POSITRON EMISSION TOMOGRAPHY (PET).: A form of nuclear medicine scanning that measures brain activity using low doses of a radioactive substance.
POST-AXIAL POLYDACTYLY.: An extra finger or toe on the outside of the hand or foot.
POST-ICTAL STATE.: A period of lethargy, confusion, and deep breathing following a grand mal seizure that may last from a few minutes to several hours.
POSTAXIAL POLYDACTYLY.: Occurring near the little finger (pinky) or the little toe.
POSTERIOR COLUMN.: Long fiber tracts that run in the spinal cord, carrying vibratory and position sense from the limbs to the brain.
POSTERIOR FOSSA.: Area at the base of the skull attached to the spinal cord.
POVERTY OF SPEECH.: A negative symptom of schizophrenia, characterized by brief and empty replies to questions. It should not be confused with shyness or reluctance to talk.
PRADER-WILLI SYNDROME.: A syndrome caused by a deletion in the paternally inherited chromosome 15 or by uniparental disomy of the maternal chromosome 15.
PRE-AXIAL POLYDACTYLY.: An extra finger or toe on the inside of the hand or foot.
PREAURICULAR PITS.: Small pits in the skin on the outside of the ear.
PREAXIAL POLYDACTYLY.: Occurring near the thumb or the big toe.
PRECOCIOUS PUBERTY.: An abnormal condition in which a person undergoes puberty at a very young age. This condition causes the growth spurt associated with puberty to occur before the systems of the body are ready, which causes these individuals not to attain normal adult heights.
PRECURSOR COMPONENTS.: Components in an enzymatic pathway that are formed by previous cellular events.
PREMUTATION.: A change in a gene that precedes a mutation; this change does not alter the function of the gene.
PRENATAL DIAGNOSIS.: The determination of whether a fetus possesses a disease or disorder while it is still in the womb.
PRENATAL TESTING.: Testing for a disease, such as a genetic condition, in an unborn baby.
PRENATAL ULTRASOUND.: An imaging test using high-frequency sound waves to create images of internal organs. Prenatal indicates the test is preformed on a fetus while still in the womb.
PREVALENCE.: The number of cases of a disease in a population at a specific period of time.
PRIMARY ATRIAL SEPTATION.: An improper division of the atria of the heart, or a "hole in the heart," which results in the formation of a common atrium rather than the normal two-chambered atrium.
PRIMARY CANCER.: The first or original cancer site, before any metastasis.
PRIMARY CRANIOSYNOSTOSIS.: Abnormal closure of the cranial sutures caused by an abnormality in the sutures themselves.
PRIMARY DYSTONIA.: Dystonia that has no connection to disease or injury. Often hereditary.
PRIMARY IMMUNODEFICIENCY DISEASE (PID).: A group of approximately 70 conditions that affect the normal functioning of the immune system.
PRIMARY POSITION, PRIMARY GAZE.: When both eyes are looking straight ahead.
PRIMARY TUMOR.: The organ or tissue where the tumor began.
PRION.: A term coined to mean "proteinaceous infectious particle." Prior to the 1982 discovery of prions, it was not believed that proteins could serve as infectious agents.

PROBAND.: The person in the family who is affected by a genetic disorder and who brings the family to the attention of a health care provider.
PROGERIA.: Genetic abnormality that presents initially as premature aging and failure to thrive in children.
PROGNATHISM.: A protruding lower jaw.
PROLACTIN.: A hormone that helps the breast prepare for milk production during pregnancy.
PROLIFERATION.: The growth or production of cells.
PROMOTER.: The region of a gene that initiates transcription of the genetic information.
PROPHYLACTIC.: Preventing disease.
PROPIONIC ACID.: An organic compound that builds up in the body if the proper enzymes are not present.
PROPIONYL COA CARBOXYLASE.: An enzyme that breaks down the amino acids isoleucine, valine, threonine, and methionine.
PROPTOSIS.: Bulging eyeballs.
PROSTATECTOMY.: The surgical removal of the prostate gland.
PROTANOPIA.: The inability of difficulty in distinguishing blue and yellow colors.
PROTEASE.: An enzyme that acts as a catalyst in the breakdown of peptide bonds.
PROTEIN.: Important building blocks of the body, composed of amino acids, involved in the formation of body structures and controlling the basic functions of the human body.
PROTEINURIA.: Excess protein in the urine.
PROTEOLIPID PROTEIN GENE (PLP).: A gene that makes a protein that is part of the myelin in the central nervous system. Mutations in this gene cause PMD.
PROTO-ONCOGENE.: A gene involved in stimulating the normal growth and division of cells in a controlled manner.
PROTOPORPHYRIN.: A precursor molecule to the porphyrin molecule.
PROXIMAL.: Near the point of origin.
PROXIMAL MUSCLES.: The muscles closest to the center of the body.
PSEUDOAINHUM.: Constrictions of the skin seen in Vohwinkel disease that may lead to damage to the hands of the feet and possible amputation of the affected areas.
PSEUDOAUTOSOMAL DOMINANT INHERITANCE.: The pattern of inheritance for a disorder caused by genes in the pseudoautosomal regions of the sex chromosomes. Individuals only require one mutated or nonworking copy of a gene to have signs and symptoms of the disorder. Affected individuals have a 50% chance to have an affected child with each pregnancy.
PSEUDOAUTOSOMAL REGION.: Genes found on the sex chromosomes that contain the same genetic information whether they are on the X or Y chromosome.
PSEUDOCAMPTODACTYLY.: A condition in which the fingers curve or bend when the hand is bent back at the wrist.
PSEUDOCYST.: A fluid-filled space that may arise in the setting of pancreatitis.
PSEUDODEMENTIA.: A term for a depression with symptoms resembling those of dementia. The term dementia of depression is now preferred.
PSEUDODOMINANT.: A recessive trait that appears, in a pedigree analysis, to be a dominant trait.
PSEUDOTUMOR CEREBRI.: A syndrome of raised pressure within the skull that may cause vomiting, headache, and double vision.
PSORIASIS.: A common, chronic, scaly skin disease.
PSYCHODYNAMIC THERAPIES.: A form of psychological counseling that seeks to determine and resolve the internal conflicts that may be causing an individual to be suffering from the symptoms of depression.
PSYCHOLOGIST.: An individual who specializes in the science of the mind.
PSYCHOMOTOR.: Movement produced by action of the mind or will.
PSYCHOSIS.: A severe mental disorder characterized by loss of contact with reality, causing deterioration of normal social functioning.
PSYCHOTHERAPY.: Psychological counseling that seeks to determine the underlying causes of a patient's depression. The form of this counseling may be cognitive/behavioral, interpersonal, or psychodynamic.
PSYCHOTIC DISORDER.: A mental disorder characterized by delusions, hallucinations, or other symptoms suggesting a lack of contact with reality. The schizophrenias are psychotic disorders.
PTERYGIUM COLLI.: Webbing or broadening of the neck, usually found at birth, and usually on both sides of the neck.
PTOSIS.: Drooping of the upper eyelid.

PUBERTY.: Point in development when the gonads begin to function and secondary sexual characteristics begin to appear.
PULMONARY ARTERY.: An artery that carries blood from the heart to the lungs.
PULMONARY ATRESIA.: When there is no valve between the right ventricle and the pulmonary artery (the artery leading from the heart to the lungs). In the absence of this valve, the blood does not flow into the lungs well.
PULMONARY EDEMA.: A problem caused when fluid backs up into the veins of the lungs. Increased pressure in these veins forces fluid out of the vein and into the air spaces (alveoli). This interferes with the exchange of oxygen and carbon dioxide in the alveoli.
PULMONARY HYPERTENSION.: A severe form of high blood pressure caused by diseased arteries in the lung.
PULMONARY HYPOPLASIA.: Underdevelopment of the lungs.
PULMONARY STENOSIS.: Narrowing of the pulmonary valve of the heart, between the right ventricle and the pulmonary artery, limiting the amount of blood going to the lungs.
PULMONOLOGIST.: A physician who specializes in lung diseases.
PUMICE STONE.: A small stone used to wear down thickened areas of the skin.
PUNCTATED.: Having a dotted pattern.
PUPIL.: The opening in the iris through which light entering the eye.
PUSTULE.: A pus-filled lesion of the skin that resembles the "pimples" of adolescent acne.
PYELONEPHRITIS.: Inflammation of the kidney commonly caused by bacterial infections.
PYGOPAGUS.: Conjoined twins who are joined back to back with fused buttocks.
PYLORIC SPHINCTER.: Circular smooth muscle found at the outlet of the stomach.
PYLORIC STENOSIS.: Narrowing of the stomach due to thickening of the pyloris muscle at the end of the stomach.
PYOGENIC.: Pus forming.
PYREXIA.: A medical term denoting fevers.
PYRIDOSTIGMINE BROMIDE (MESTINON).: An anticholinesterase drug used in treating myasthenia gravis.
PYRUVATE CARBOXYLASE.: The enzyme that is responsible for the first step in the conversion of pyruvate molecules into glucose molecules. Type A PCD affected individuals produce an highly inefficient form of pyruvate carboxylase. Type B PCD affected individuals either completely lack the ability to produce this enzyme, or they cannot produce it in sufficient quantities to sustain life.
PYRUVATE DEHYDROGENASE COMPLEX.: A series of enzymes and co-factors that allow pyruvate to be converted into a chemical that can enter the TCA cycle.

Q

QT INTERVAL.: The section on an electrocardiogram between the start of the QRS complex and the end of the T wave, representing the firing or depolarization of the ventricles and the period of recovery prior to repolarization, or recharging, for the next contraction.
QUADRIPLEGIA.: Paralysis of all four limbs.

R

RACHITIC.: Pertaining to, or affected by, rickets. Examples of rachitic deformities include curved long bones with prominent ends, a prominent middle chest wall, or bony nodules at the inner ends of the ribs.
RADIAL KERATOTOMY (RK).: A surgical procedure involving the use of a diamond-tipped blade to make several spoke-like slits in the peripheral (non-viewing) portion of the cornea to improve the focus of the eye and correct myopia by flattening the cornea.
RADIATION.: High-energy rays used in cancer treatment to kill or shrink cancer cells.
RADIATION THERAPY.: Treatment using high-energy radiation from x-ray machines, cobalt, radium, or other sources.
RADICULOPATHY.: A bulging of disc material often irritating nearby nerve structures resulting in pain and neurologic symptoms. A clinical situation where the radicular nerves (nerve roots) are inflamed or compressed. This compression by the bulging disc is referred to as a radiculopathy. This problem tends to occur most commonly in the neck (cervical spine) and low back (lumbar spine).
RADIOGRAPHIC.: Involving an x ray.
RADIOLUCENT.: Transparent to x ray or radiation. The black area on x-ray film.
RANSON CRITERIA.: A system of measurements, including age and blood testing, used to predict the outcome of a person who has been hospitalized for an episode of pancreatitis.

RAYNAUD PHENOMENON/RAYNAUD DISEASE.: A condition in which blood flow to the body's tissues is reduced by a malfunction of the nerves that regulate the constriction of blood vessels. When attacks of Raynaud's occur in the absence of other medical conditions, it is called Raynaud disease. When attacks occur as part of a disease (as in scleroderma), it is called Raynaud phenomenon.
RECESSIVE.: Refers to an inherited trait that is outwardly obvious only when two copies of the gene for that trait are present. An individual displaying a recessive trait must have inherited one copy of the defective gene from each parent.
RECESSIVE GENE.: A type of gene that is not expressed as a trait unless inherited by both parents.
RECESSIVE TRAIT.: An inherited trait or characteristic that is outwardly obvious only when two copies of the gene for that trait are present.
RECTUM.: The end portion of the intestine that leads to the anus.
RECURRENCE RISK.: The possibility that the same event will occur again.
RECURRENT.: Tendency to repeat.
RED BLOOD CELLS.: Hemoglobin-containing blood cells that transport oxygen from the lungs to tissues. In the tissues, the red blood cells exchange their oxygen for carbon dioxide, which is brought back to the lungs to be exhaled.
RED NUCLEUS.: A small structure present in the brainstem that is involved in the control of movement.
REDUCED PENETRANCE.: Failing to display a trait or disease despite possessing the dominant gene that determines it.
REFRACTION.: The bending of light rays as they pass from one medium through another. Used to describe the action of the cornea and lens on light rays as they enter they eye. Also used to describe the determination and measurement of the eye's focusing system by an optometrist or ophthalmologist.
REFRACTIVE EYE SURGERY.: A general term for surgical procedures that can improve or correct refractive errors by permanently changing the shape of the cornea.
RENAL.: Related to the kidneys.
RENAL AGENESIS.: Complete absence of one or both kidneys.
RENAL CELL CARCINOMA.: A cancerous tumor made from kidney cells.
RENAL COLIC.: A spasmodic pain, moderate to severe in degree, located in the back, side and/or groin area.
RENAL DYSPLASIA.: A developmental anomaly of the kidney.
RENAL HYPOPLASIA.: Abnormally small kidneys.
RENAL SYSTEM.: The organs involved with the production and output of urine.
RENIN.: An enzyme produced by the kidneys.
RENPENNING SYNDROME.: X-linked mental retardation with short stature and microcephaly not associated with the fragile X chromosome and occurring more frequently in males, although some females may also be affected.
REPLICATE.: Produce identical copies of itself.
REPOLARIZATION.: Period when the heart cells are at rest, preparing for the next wave of electrical current (depolarization).
RESPIRATORY.: Having to do with breathing.
RETICULOCYTE.: Immature red blood cells.
RETINA.: The inner, light-sensitive layer of the eye containing rods and cones. The retina transforms the image it receives into electrical signals that are sent to the brain via the optic nerve.
RETINAL DYSPLASIA.: Improper development of the retina that can lead to detachment of the retina.
RETINAL DYSTROPHY.: Degeneration of the retina, causing a decline in visual clarity.
RETINAL LACUNAE.: Small abnormal cavities or holes in the retina.
RETINAL PIGMENT EPITHELIUM (RPE).: The pigmented cell layer that nourishes the retinal cells; located just outside the retina and attached to the choroid.
RETINITIS PIGMENTOSA.: Progressive deterioration of the retina, often leading to vision loss and blindness.
RETINOIDS.: A derivative of synthetic Vitamin A.
RETINOPATHY.: Any disorder of the retina.
RHABDOMYOLYSIS.: Breakdown or disintegration of muscle tissue.
RHABDOMYOSARCOMA.: A malignant tumor of the skeletal muscle.
RHEUMATOID ARTHRITIS.: Chronic, autoimmune disease marked by inflammation of the membranes surrounding joints.

RHEUMATOID FACTOR.: Antibodies present in the majority of individuals with rheumatoid arthritis. A diagnostic marker for rheumatoid arthritis that is absent from ankylosing spondylitis and other seronegative spondyloarthopathies.
RHINITIS.: Infection of the nasal passages.
RHIZOMELIA.: A term used to describe the physical growth difference of short arms and legs.
RHIZOMELIC.: Disproportionate shortening of the upper part of a limb compared to the lower part of the limb.
RHO/RAC GUANINE EXCHANGE FACTOR.: Member of a class of proteins that appear to convey signals important in the structure and biochemical activity of cells.
RICKETS.: A condition caused by the dietary deficiency of vitamin D, calcium, and usually phosphorus, seen primarily in infancy and childhood, and characterized by abnormal bone formation.
RING CHROMOSOME.: An abnormal chromosome in which the terminal ends of the short (p) and long (q) arms have been lost and the remaining p and q arms subsequently join to form a ring.
RNA.: Ribonucleic acid, the intermediate step between DNA and its final expression product. DNA is transcribed into RNA and RNA is translated into protein.
ROD.: Photoreceptor that is highly sensitive to low levels of light and transmits images in shades of gray.
RUSSELL SYNDROME.: An alternative term for Russell-Silver syndrome. Many doctors use this term to mean a Russell-Silver syndrome affected individual who does not have body asymmetry.

S

SACROILIAC JOINT.: The joint between the triangular bone below the spine (sacrum) and the hip bone (ilium).
SACROILIITIS.: Inflammation of the sacroiliac joint.
SACRUM.: Triangular bone at the base of the spinal column.
SADDLE NOSE.: A sunken nasal bridge.
SARCOIDOSIS.: A chronic disease characterized by nodules forming in the lymph nodes, lungs, bones, and skin.
SARCOPLASMIC RETICULUM.: A system of tiny tubes located inside muscle cells that allow muscles to contract and relax by alternatively releasing and storing calcium.
SATELLITES OF CHROMOSOMES.: Small segments of genetic material at the tips of the short arms of chromosomes 13, 14, 15, 21, and 22.
SAVANT SKILLS.: Unusual talents, usually in art, math, or music, that some individuals with autism have in addition to the deficits of autism.
SCAPHOCEPHALY.: An abnormally long and narrow skull.
SCAPULA.: Shoulder blade.
SCAPULAR WINGING.: The jutting back of the shoulder blades that can be caused by muscle weakness.
SCHIZENCEPHALY.: Abnormality of the brain in which there are deep ruts and clefts in the surface of the brain.
SCINTIGRAPHY.: Injection and detection of radioactive substances to create images of body parts.
SCLERA.: The tough white membrane that forms the outer layer of the eyeball.
SCLERODERMA.: A relatively rare autoimmune disease affecting blood vessels and connective tissue that makes skin appear thickened.
SCLEROSIS.: Hardening.
SCOLIOMETER.: A tool for measuring trunk asymmetry; it includes a bubble level and angle measure.
SCOLIOSIS.: An abnormal side-to-side curvature of the spine.
SCREENING.: Process through which carriers of a trait may be identified within a population.
SEBACEOUS.: Related to the glands of the skin that produce an oily substance.
SECOND-DEGREE RELATIVE.: Aunts, uncles, nieces, nephews, grandparents, grandchildren and half siblings are second-degree relatives. These individuals have one fourth of their genes in common.
SECONDARY CRANIOSYNOSTOSIS.: Abnormal closure of the cranial sutures caused by a failure of the brain to grow and expand.
SECONDARY DYSTONIA.: Dystonia that is occurs due to disease, injury, or another non-hereditary factor. Also known as symptomatic dystonia.
SEDATIVE.: Medication that has a soothing or tranquilizing effect.
SEIZURE.: A sudden attack, spasm, or convulsion.
SEMEN.: A whitish, opaque fluid released at ejaculation that contains sperm.

SEMI-DOMINANT.: A trait expressed as a severe form in homozygous affected individuals and a milder form in heterozygous affected individuals.
SEMINAL VESICLES.: The pouches above the prostate that store semen.
SEMINEFEROUS TUBULES.: Long, threadlike tubes that are packed in areolar tissue in the lobes of the testes.
SENSITIVITY.: The proportion of people with a disease who are correctly diagnosed (test positive based on diagnostic criteria). The higher the sensitivity of a test or diagnostic criteria, the lower the rate of "false negatives," people who have a disease but are not identified through the test.
SENSITIZATION.: Change in immune system so that it identifies and "remembers" specific properties of an antigen.
SENSORINEURAL HEARING LOSS (SNHL).: Hearing loss caused by damage to the nerves or parts of the inner ear governing the sense of hearing. Sound is conducted normally through the external and middle ear.
SENSORY NEURONS.: Class of neurons that specifically regulate and control external stimuli (senses: sight, sound).
SEPSIS.: An infection of the bloodstream.
SEPTAL.: Relating to the septum, the thin muscle wall dividing the right and left sides of the heart. Holes in the septum are called septal defects.
SEPTUM PELLUCIDUM.: A membrane between two of the normal cavities of the brain that prevents electrical signals from passing between different portions of the brain.
SEQUENCE.: The combination of both a primary structural or functional anomaly, and the secondary anomalies produced by any abnormal forces or processes it generates.
SERIAL CASTING.: A series of casts designed to gradually move a limb into a more functional position.
SEROLOGICAL.: Pertaining to serology, the science of testing blood to detect the absence or presence of antibodies (an immune response) to a particular antigen (foreign substance).
SEROSITIS.: Inflammation of a serosal membrane. Polyserositis refers to the inflammation of two or more serosal membranes.
SEROTONIN DOPAMINE ANTAGONIST (SDA).: The newer second-generation antipsychotic drugs, also called atypical antipsychotics. SDAs include clozapine (Clozaril), risperidone (Risperdal), and olanzapine (Zyprexa).
SEROTYPE.: One form of a bacteria that has unique surface proteins. Each serotype causes a unique antibody response from a person's immune system.
SERUM.: The liquid part of blood, from which all the cells have been removed.
SERUM CK TEST.: A blood test that determines the amount of the enzyme creatine kinase (CK) in the blood serum. An elevated level of CK in the blood indicates that muscular degeneration has occurred and/or is occurring.
SERUM CREATININE.: A chemical in the urine of kidney patients used to determine kidney disease and failure. Elevated levels of serum creatinine are an early marker for severe kidney disease or failure.
SEVERE COMBINED IMMUNODEFICIENCY (SCID).: A group of rare, life-threatening diseases present at birth, that cause a child to have little or no immune system. As a result, the child's body is unable to fight infections.
SEX-LINKED.: Refers to genes or traits carried on one of the sex chromosomes, usually the X.
SEX-LINKED DISORDER.: A disorder caused by a gene located on a sex chromosome, usually the X chromosome.
SEX CHROMOSOMES.: The X and Y chromosomes that determine the sex of the individual.
SHOCK.: An inability to provide the body with the oxygen it requires, sometimes due to large amounts of bleeding or fluid loss.
SHORT RIB POLYDACTYLY SYNDROMES.: A collection of genetic disorders characterized by abnormally short ribs and extra fingers or toes. Research is ongoing to determine if these disorders are the result of mutations in a common gene.
SHORT STATURE.: Shorter than normal height; can include dwarfism. Defined as height of less than three standard deviations from the mean for age, race, and gender.
SHORT TRUNK.: An abnormally short torso or body.
SHUNT.: A small tube placed in a ventricle of the brain to direct cerebrospinal fluid away from the blockage into another part of the body.
SIALIC ACID.: N-acetylneuraminic acid, a sugar that is often at the end of an oligosaccharide on a glycoprotein.
SICKLE CELL.: A red blood cell that has assumed a elongated shape due to the presence of hemoglobin S.

SICKLE CELL ANEMIA.: A chronic, inherited blood disorder characterized by sickle-shaped red blood cells. It occurs primarily in people of African descent, and produces symptoms including episodic pain in the joints, fever, leg ulcers, and jaundice.
SIGMOIDOSCOPY.: The visual examination of the inside of the rectum and sigmoid colon, using a lighted, flexible tube connected to an eyepiece or video screen for viewing.
SILVER SYNDROME.: An alternative term for Russell-Silver syndrome. Many doctors use this term to mean a Russell-Silver syndrome affected individual who also has body asymmetry.
SITUS SOLITUS.: Normal organ placement in the body with the heart, stomach, and spleen placed towards the left, and the liver and gallbladder on the right.
SJÖGREN SYNDROME.: A chronic inflammatory disease often associated with rheumatoid arthritis.
SKELETAL DYSPLASIA.: A group of syndromes consisting of abnormal prenatal bone development and growth.
SKELETAL MUSCLE.: Muscle under voluntary control that attaches to bone and controls movement.
SKEWED INACTIVATION.: Random inactivation of either the paternally or maternally derived X chromosome in the female; also called Lyonization, and occurs early in embryonic development.
SKIN ERYTHEMA.: Irregular red streaks of skin.
SKIN HEMATOMA.: Blood from a broken blood vessel that has accumulated under the skin.
SLEEP APNEA.: A sleep disorder characterized by periods of breathing cessation lasting for 10 seconds or more.
SLEEP PARALYSIS.: An abnormal episode of sleep in which the patient cannot move for a few minutes, usually occurring on falling asleep or waking up. Often found in patients with narcolepsy.
SLY DISEASE.: Autosomal recessive metabolic disorder caused by dysfunction of the lysosomal enzyme beta-glucuronidase.
SMALL INTESTINE.: The part of the digestive tract in-between the stomach and the large intestine.
SMALL TESTES.: Refers to the size of the male reproductive glands, located in the cavity of the scrotum.
SOMATIC.: Relating to the nonreproductive parts of the body.
SOMATIC CELLS.: All the cells of the body except for the egg and sperm cells.
SOMATIC GENE THERAPY.: The introduction of genes into tissue or cells to treat a genetic related disease in an individual.
SOMATOSTATIN.: A body chemical, known as a cyclic peptide, involved in the release of human growth hormone from the pituitary gland.
SORE.: An open wound or a bruise or lesion on the skin.
SPASMODIC DYSPHONIA.: A focal dystonia that causes involuntary "spasms" of the vocal cords—leading to interruptions of speech and a decrease in voice quality.
SPASTIC.: A condition in which the muscles are rigid, posture may be abnormal, and fine motor control is impaired.
SPASTIC PARAPLEGIA.: Inability to walk, due to lack of proper neural control over the leg muscles.
SPASTICITY.: Increased muscle tone, or stiffness, which leads to uncontrolled, awkward movements.
SPECIFICITY.: The proportion of people without a disease who are correctly classified as healthy or not having the disease (test negative based on diagnostic criteria). The higher the specificity of a test or diagnostic criteria, the lower the number of "false positives," people who don't have a disease but who "test" positive.
SPEECH THERAPIST.: Person who specializes in teaching simple exercises to improve speech.
SPERMATOZOA.: Mature male germ cells that develop in the seminiferous tubules of the testes.
SPHEROCYTES.: Red blood cells that are spherical in shape, as opposed to the normal bi-concave shape. Spherocytes are more rigid and their membranes more fragile than normally shaped red blood cells.
SPHINGOMYELIN.: A group of sphingolipids containing phosphorus.
SPHINGOMYELINASE.: Enzyme required to breakdown sphingomyelinase.
SPHYGMOMANOMETER.: An inflatable cuff used to measure blood pressure.
SPINA BIFIDA OCCULTA.: A birth defect (a congenital malformation) in which part of the vertebrae fail to develop completely so that a portion of the spinal cord, which is normally protected within the vertebral column, is exposed. People with spina bifida can suffer from bladder and bowel incontinence, cognitive (learning) problems, and limited mobility.

SPINAL TAP.: A procedure by which a needle is inserted into the space between two lumbar vertebrae to obtain fluid that circulates around the spinal cord.
SPLAY.: Turned outward or spread apart.
SPLEEN.: Organ located in the upper abdominal cavity that filters out old red blood cells and helps fight bacterial infections. Responsible for breaking down spherocytes at a rapid rate.
SPLENIC FLEXURE.: The area of the large intestine at which the transverse colon meets the descending colon.
SPLENOMEGALY.: Enlargement of the spleen.
SPONDYLOSIS.: Arthritis of the spine.
SPONGIFORM ENCEPHALOPATHY.: A form of brain disease characterized by a "spongelike" appearance of the brain either on autopsy or via magnetic resonance imaging (MRI).
SPONTANEOUS.: Occurring by chance.
SPONYLOARTHRITIS (SPONDYLITIS).: Inflammatory disease of the joints of the spine.
SPORADIC.: Occurring at random or by chance, not as a result of a genetically determined or inherited trait.
SPORADIC INHERITANCE.: A status that occurs when a gene mutates spontaneously to cause the disorder in a person with no family history of the disorder.
SPUTUM.: A mixture of saliva and mucus from the lungs.
STAGE.: The extent of the tumor. Tests will be done to determine if the tumor is localized to the organ or if it has spread to the lymph nodes and/or other organs. Treatment depends upon the stage of the cancer.
STAGING.: A method of describing the degree and location of cancer.
STATIC ENCEPHALOPATHY.: A disease of the brain that does not get better or worse.
STELLATE.: A star-like, lacy white pattern in the iris. Most often seen in light-eyed individuals.
STENOSIS.: The constricting or narrowing of an opening or passageway.
STENT.: A tubular device made of metal or plastic that is inserted into a body duct or tube to prevent collapse, blockage, or overgrowth.
STETHOSCOPE.: An instrument used for listening to sounds within the body, such as those in the heart or lungs.
STILLBIRTH/STILLBORN.: The birth of a baby who has died sometime during the pregnancy or delivery.
STOMACH.: An organ that holds and begins digestion of food.
STRABISMUS.: Improper balance of the ocular muscles resulting in crossed or divergent eyes.
STROKE.: A sudden neurological condition related to a block of blood flow in part of the brain, which can lead to a variety of problems, including paralysis, difficulty speaking, difficulty understanding others, or problems with balance.
STROMA.: Middle layer of the cornea, representing about 90% of the entire cornea.
SUBARACHNOID SPACE.: The space between two membranes surrounding the brain, the arachnoid and pia mater.
SUBCORTICAL BAND HETEROTOPIA.: A mild form of lissencephaly type 1 in which abnormal bands of gray and white matter are present beneath the cortex near the ventricles.
SUBCORTICAL INFARCT.: An area of necrosis (tissue death) below the cerebral cortex of the brain resulting from obstruction of circulation to that area.
SUBMETACENTRIC.: Positioning of the centromere between the center and the top of the chromosome.
SUBSTANTIA NIGRA.: One of the movement control centers of the brain.
SUDDEN INFANT DEATH SYNDROME (SIDS).: The general term given to "crib deaths" of unknown causes.
SULFATE.: A chemical compound containing sulfur and oxygen.
SUTURE.: "Seam" that joins two surfaces together.
SYMPHALANGISM.: Fusion of phalanges at their ends.
SYMPTOMATIC CARRIER.: A heterozygous person who carries a semi-dominant trait. This person experiences milder characteristics of this trait than a person who is homozygous or hemizygous in this trait.
SYNCHRONOUS.: Occurring simultaneously.
SYNCOPE.: A brief loss of consciousness caused by insufficient blood flow to the brain.
SYNDACTYLY.: Webbing or fusion between the fingers or toes.
SYNDROME.: A group of signs and symptoms that collectively characterize a disease or disorder.
SYNDROMIC HEARING LOSS.: Hearing loss accompanied by other symptoms that characterize a larger genetic syndrome of which hearing loss is just one of the characteristics.

SYNKINESIA.: Occurs when part of the body will move involuntarily when another part of the body moves.
SYNOPHRYS.: A feature in which the eyebrows join in the middle. Also called blepharophimosis.
SYNOVITIS.: Inflammation of the synovium, a membrane found inside joints.
SYRINGOMYELIA.: Excessive fluid in the spinal cord.
SYSTEMIC SCLEROSIS.: A rare disorder that causes thickening and scarring of multiple organ systems.
SYSTOLIC BLOOD PRESSURE.: Blood pressure when the heart contracts (beats).

T

TACHYCARDIA.: An excessively rapid heartbeat; a heart rate above 100 beats per minute.
TAI-CHI.: A Chinese system of physical exercises that uses slow, smooth body movements to help with posture control and relaxation.
TALIPES EQUINOVARUS.: A type of club-foot characterized by a downward and inward pointing foot.
TAY-SACHS DISEASE.: An inherited biochemical disease caused by lack of a specific enzyme in the body. In classical Tay-Sachs disease, previously normal children become blind and mentally handicapped, develop seizures, and decline rapidly. Death often occurs between the ages of three to five years. Tay-Sachs disease is common among individuals of eastern European Jewish background but has been reported in other ethnic groups.
TCA CYCLE.: Formerly know as the Kreb's cycle, this is the process by which glucose and other chemicals are broken down into forms that are directly useable as energy in the cells.
TELANGIECTASIA.: Abnormal dilation of capillary blood vessels leading to the formation of telangiectases or angiomas.
TELANGIECTASIS.: A spidery red skin lesion caused by dilated blood vessels.
TELANGIECTATIC.: Refers to a localized collection of distended blood capillary vessels.
TELESCOPING.: A term sometimes used to describe the relatively rapid progression of alcoholism in women, even though women usually begin to drink heavily at later ages than men do.
TELOGEN.: The resting phase of the hair growth cycle.
TENDON.: A strong connective tissue that connects muscle to bone.
TENDON REFLEX.: Reflex contraction of the muscle that is observed by tapping on its tendon.
TENOTOMY.: A surgical procedure that cuts the tendon of a contracted muscle to allow lengthening.
TENSILON TEST.: A test for diagnosing myasthenia gravis. Tensilon is injected into a vein and, if the person has MG, their muscle strength will improve for about five minutes.
TERATOGEN.: Any drug, chemical, maternal disease, or exposure that can cause physical or functional defects in an exposed embryo or fetus.
TERATOGENIC.: Any agent that can cause birth defects or mental retardation in a developing fetus. Common teratogens are medications or other chemicals but they also include infections, radiation, maternal medical condition, and other agents.
TERATOGENIC FACTOR.: Any factor that can produce congenital abnormalities.
TERMINAL DELETION.: The abnormal early termination of a chromosome caused by the deletion of one of its ends.
TESTES.: The male reproductive organs that produce male reproductive cells (sperm) and male hormones.
TESTICLES.: Two egg-shaped glands that produce sperm and sex hormones.
TESTOSTERONE.: Hormone produced in the testicles that is involved in male secondary sex characteristics.
TETRALOGY OF FALLOT.: A congenital heart defect consisting of four (tetralogy) associated abnormalities: ventricular septal defect (VSD—hole in the wall separating the right and left ventricles); pulmonic stenosis (obstructed blood flow to the lungs); the aorta "overrides" the ventricular septal defect; and thickening (hypertrophy) of the right ventricle.
TETRAPHOCOMELIA.: Absence of all, or a portion of, all four limbs. The hands or feet may be attached directly to the trunk.
TETRAPLEGIA.: Paralysis of all four limbs. Also called quadriplegia.
TETRAPLOIDY.: A form of polyploidy; four sets of chromosomes.
TETRASOMY.: Referring to the presence of four parts or copies of a chromosome or part of a chromosome.

THALAMUS.: A pair of large egg-shaped structures near the brainstem that act as the main sensory relay station and help with control of movement.
THALASSEMIA.: An inherited group of anemias occurring primarily among people of Mediterranean descent. It is caused by defective formation of part of the hemoglobin molecule.
THALIDOMIDE.: A mild sedative that is teratogenic, causing limb, neurologic, and other birth defects in infants exposed during pregnancy. Women used thalidomide (early in pregnancy) in Europe and in other countries between 1957 and 1961. It is still available in many places, including the United States, for specific medical uses (leprosy, AIDS, cancer).
THERMOLABILE.: Heat-sensitive. A thermolabile protein is a protein that easily loses its shape when heated even only slightly.
THORACIC CAVITY.: The chest.
THORACOPAGUS.: Conjoined twins joined at the upper body who share a heart.
THORAX.: Chest cavity.
THROMBOCYTOPENIA.: A persistent decrease in the number of blood platelets usually associated with hemorrhaging.
THROMBOEMBOLISM.: A condition in which a blood vessel is blocked by a free-floating blood clot carried in the blood stream.
THYMUS GLAND.: An endocrine gland located in the front of the neck that houses and transports T cells, which help to fight infection.
THYROID GLAND.: A gland located in the front of the neck that is responsible for normal body growth and metabolism. The thyroid traps a nutrient called iodine and uses it to make thyroid hormones, which allow for the breakdown of nutrients needed for growth, development and body maintenance.
THYROID STIMULATING HORMONE (THYROTROPIN).: A hormone that stimulates the thyroid gland to produce hormones that regulate metabolism.
THYROXINE (T4) AND TRIIODOTHYRONINE (T3).: Thyroid hormones.
TIC.: Brief and intermittent involuntary movement or sound.
TISSUE.: Group of similar cells that work together to perform a particular function. The four basic types of tissue include muscle, nerve, epithelial, and connective tissues.
TITUBATION.: Tremor of the head.
TONE.: A term used to describe the tension of muscles. Increased tone is increased tension in the muscles.
TONOMETER.: A device used to measure fluid pressures of the eye.
TORSADE DE POINTES.: A type of tachycardia of the ventricles that is characteristic of Long-QT syndrome and Jervell and Lange Nielsen syndrome.
TORTICOLLIS.: Twisting of the neck to one side that results in abnormal carriage of the head and is usually caused by muscle spasms. Also called wryneck.
TORTUOUS.: Having many twists or turns.
TOXIC.: Poisoinous.
TRABECULAR MESHWORK.: A sponge-like tissue that drains the aqueous humor from the eye.
TRACHEA.: The windpipe. A tube composed of cartilage and membrane that extends from below the voice box into the chest where it splits into two branches, the bronchi, that lead to each lung.
TRACHEO-ESOPHAGEAL FISTULA.: Abnormal connection between trachea and esophagus, frequently associated with the esophagus ending in a blind pouch.
TRACHEOSTOMY.: An opening surgically created through the neck into the trachea (windpipe) to improve breathing.
TRACTION ALOPECIA.: Hair loss caused by pressure or tension on the scalp related to certain types of hair styles or equipment worn on the head.
TRAIT.: The set of physically observable characteristics that results from the expression of a gene.
TRANS-RECTAL ULTRASOUND.: A procedure where a probe is placed in the rectum. High-frequency sound waves that cannot be heard by humans are sent out from the probe and reflected by the prostate. These sound waves produce a pattern of echoes that are then used by the computer to create sonograms or pictures of areas inside the body.
TRANSCRIPTION.: The process by which genetic information on a strand of DNA is used to synthesize a strand of complementary RNA.
TRANSCRIPTION FACTOR.: A protein that works to activate the transcription of other genes.
TRANSFERASES.: Family of enzymes that transfer a specific chemical group from one molecule to another.
TRANSFUSION.: The injection of a component of the blood from a healthy person into the circulation of a person who is lacking or deficient in that same component of the blood.

TRANSGENIC EXPERIMENT.: A genetic experiment in which a gene can be added to a laboratory animal's genetic material. The behavior of the altered animal can be compared with the behavior of an unaltered animal to help pinpoint the role of the gene in affecting it.
TRANSIENT ISCHEMIC ATTACK (TIA).: A temporary interruption of blood flow to a part of the brain; causes symptoms that are similar to a stroke, but temporary.
TRANSLATION.: The process by which RNA is changed into protein.
TRANSLOCATION.: The transfer of one part of a chromosome to another chromosome during cell division. A balanced translocation occurs when pieces from two different chromosomes exchange places without loss or gain of any chromosome material. An unbalanced translocation involves the unequal loss or gain of genetic information between two chromosomes.
TRANSMEMBRANE.: Anything that spans the width of a membrane.
TRANSPLANTATION.: The implanting of an organ from either a deceased person (cadaver) or from a live donor to a person whose organ has failed.
TRANSPOSITION OF THE GREAT ARTERIES.: A reversal of the two great arteries of the heart, causing oxygenated blood to be carried back to the lungs and blood that is lacking in oxygen to be transported throughout the body.
TRANSVAGINAL ULTRASOUND.: A way to view the ovaries using sound waves. A probe is inserted into the vagina and the ovaries can be seen. Color doppler imaging measures the amount of blood flow, as tumors sometimes have high levels of blood flow.
TRANSVERSION.: A genetic termed referring to a specific substitution of one base pair for another. There are only four possible tranversions: guanine for cytosine, cytosine for guanine, adenine for thymine, or thymine for adenine.
TRAUMA.: Injury.
TRICHOTILLOMANIA.: A psychiatric disorder characterized by hair loss resulting from compulsive pulling or tugging on one's hair.
TRIGGER DRUGS.: Specific drugs used for muscle relaxation and anesthesia that can trigger an episode of malignant hyperthermia in a susceptible person. The trigger drugs include halothane, enflurane, isoflurane, sevoflurane, desflurane, methoxyflurane, ether, and succinylcholine.
TRIGLYCERIDES.: Certain combinations of fatty acids (types of lipids) and glycerol.
TRIGONOCEPHALY.: An abnormal development of the skull characterized by a triangular shaped forehead.
TRIMESTER.: A three-month period. Human pregnancies are normally divided into three trimesters: first (conception to week 12), second (week 13 to week 24), and third (week 25 until delivery).
TRINUCLEOTIDE.: A sequence of three nucleotides.
TRINUCLEOTIDE REPEAT EXPANSION.: A sequence of three nucleotides that is repeated too many times in a section of a gene.
TRIOSE PHOSPHATE ISOMERASE.: Abbreviated TPI, this is the enzyme responsible for the conversion of dihydroxyacetone phosphate (DHAP) into D-glyceralde-hyde-3-phosphate (GAP). DHAP and GAP are the two major products of a step in the multi-step process that converts glucose into ATP to supply the body with the energy that it needs to sustain itself. Only GAP can continue in this process, but DHAP is produced in much higher quantities. TPI deficiency affected people cannot change DHAP into GAP as efficiently as unaffected people can accomplish this conversion. The result is that TPI deficient people cannot produce sufficient amounts of ATP from glucose to maintain normal cell function.
TRIPHALANGEAL THUMB (TPT).: A thumb that has three bones rather than two.
TRIPLOID.: Three sets of chromosomes; in humans, this is 69 chromosomes.
TRIPLOIDY.: A form of polyploidy; three sets of chromosomes.
TRISMUS.: Inability to open the mouth completely.
TRISOMY.: An abnormal condition where three copies of one chromosome are present in the cells of an individual's body instead of two, the normal number.
TRISOMY 18.: A chromosomal alteration where a child is born with three copies of chromosome number 18 and as a result is affected with multiple birth defects and mental retardation.
TRUNCUS ARTERIOSUS.: Having only one artery coming from the heart instead of two. Often there is a ventricular septal defect (VSD) present.
TRYPSIN.: A digestive enzyme found in pancreatic fluid that breaks down proteins. This enzyme is abnormal in hereditary pancreatitis.
TRYPTOPHAN.: A crystalline amino acid widely distributed in proteins and essential to human life.

TUBULE.: A small tube lined with glandular epithelium in the kidney.
TUMOR.: An abnormal growth of cells. Tumors may be benign (noncancerous) or malignant (cancerous).
TUMOR NECROSIS FACTOR.: A protein that plays an early and major role in the rheumatic disease process.
TUMOR SUPPRESSOR GENE.: Genes involved in controlling normal cell growth and preventing cancer.
TURNER SYNDROME.: Chromosome abnormality characterized by short stature and ovarian failure, caused by an absent X chromosome. Occurs only in females.
TYMPANOPLASTY.: Any of several operations on the eardrum or small bones of the middle ear, to restore or improve hearing in patients with conductive hearing loss.
TYPE I INCONTINENTIA PIGMENTI.: Sporadic IP. This disorder is caused by mutations in the gene at Xp11. These mutations are not inherited from the parents, they are de novo mutations. This type of IP probably represents a different disease than type II IP.
TYPE II INCONTINENTIA PIGMENTI.: Familial, male-lethal, type IP. This type of IP is the "classic" case of IP. It is caused by mutations in the NEMO gene located at Xq28. Inheritance is sex-linked recessive.
TYROSINE.: An aromatic amino acid that is made from phenylalanine.

U

ULTRASONOGRAM.: An image produced by ultrasonography, a procedure where high-frequency sound waves that cannot be heard by human ears are bounced off internal organs and tissues. These sound waves produce a pattern of echoes which are then used by the computer to create sonograms, or pictures of areas inside the body.
ULTRASONOGRAPHY.: A medical test in which sound waves are directed against internal structures in the body. As sound waves bounce off the internal structure, they create an image on a video screen. Ultrasonography is often used to diagnose fetal abnormalities, gallstones, heart defects, and tumors. Also called ultrasound imaging.
UMBILICAL HERNIA.: Protrusion of the bowels through the abdominal wall, underneath the navel.
UNDESCENDED TESTICLES.: Testicles that failed to move from the abdomen to the scrotum during the development of the fetus.
UNILATERAL.: Refers to one side of the body or only one organ in a pair.
UNIPARENTAL DISOMY.: Chromosome abnormality in which both chromosomes in a pair are inherited from the same parent.
UPSHOOT.: Upward movement of the eye.
UREA.: A nitrogen-containing compound that can be excreted through the kidney.
UREA CYCLE.: A series of complex biochemical reactions that remove nitrogen from the blood so ammonia does not accumulate.
UREA CYCLE DISORDER.: A disease that is caused by a lack of an enzyme that cleans the blood of ammonia.
UREMIC POISONING.: Accumulation of waste products in the body.
URETERS.: Tubes through which urine is transported from the kidneys to the bladder.
URETHRA.: The tubular portion of the urinary tract connecting the bladder and external meatus through which urine passes. In males, seminal fluid and sperm also pass through the urethra.
URETHRITIS.: Inflammation of the urethra.
URINARY URGENCY.: An exaggerated or increased sense of needing to urinate.
URTICARIA.: Also known as hives. Usually associated with an allergic reaction.
UTERUS.: A muscular, hollow organ of the female reproductive tract. The uterus contains and nourishes the embryo and fetus from the time the fertilized egg is implanted until birth.
UVEITIS.: Inflammation of all or part of the uvea, which consists of the middle vascular portion of the eye including the iris, ciliary body, and choroid.

V

VACCINE.: An injection, usually derived from a microorganism, that can be injected into an individual to provoke an immune response and prevent future occurrence of an infection by that microorganism.
VACUOLATION.: The formation of multiple vesicles, or vacuoles, within the cytosol of cells.
VARIABLE EXPRESSION.: Instances in which an identical genetic mutation leads to varying traits from affected individual to affected individual. This variance may occur between members of two separately affected families or it may occur between affected members of the same family.

VARIABLE PENETRANCE.: A term describing the way in which the same mutated gene can cause symptoms of different severity and type within the same family.
VAS DEFERENS.: The long, muscular tube that connects the epididymis to the urethra through which sperm are transported during ejaculation.
VASCULAR.: Having to do with blood vessels.
VASCULAR MALFORMATION.: Abnormality of the blood vessels that often appears as a red or pink patch on the surface of the skin.
VASODILATOR.: A drug that relaxes blood vessel walls.
VECTORS.: Something used to transport genetic information to a cell.
VELLUS HAIRS.: The fine lighter-colored hairs that result from miniaturization.
VELO.: Derived from the latin word velum, meaning palate and back of the throat.
VENOUS.: Term used to describe a vein or the entire system of veins.
VENOUS THROMBOSIS.: A condition caused by the presence of a clot in the vein.
VENTILATOR.: Mechanical breathing machine.
VENTRAL WALL DEFECT.: An opening in the abdomen (ventral wall). Examples include omphalocele and gastroschisis.
VENTRICLE.: The fluid filled spaces in the center of the brain that hold cerebral spinal fluid.
VENTRICULAR SEPTAL DEFECT (VSD).: An opening between the right and left ventricles of the heart.
VENTRICULOPERITONEAL SHUNT.: A tube equipped with a low pressure valve, one end of which is inserted into the lateral ventricles, the other end of which is routed into the peritoneum, or abdominal cavity.
VERMIS.: The central portion of the cerebellum, which divides the two hemispheres. It functions to monitor and control movement of the limbs, trunk, head, and eyes.
VERTEBRA.: One of the 23 bones which comprise the spine. Vertebrae is the plural form.
VERTEBRAL.: Related to the vertebrae.
VERTEBRAL DIVISIONS.: The human vertebral regions are divided into cervical, thoracic, lumbar, and sacral from the neck to the tailbone.
VERY LONG CHAIN FATTY ACIDS (VLCFA).: A type of fat that is normally broken down by the peroxisomes into other fats that can be used by the body.
VESTIBULAR NERVE.: The nerve that transmits the electrical signals collected in the inner ear to the brain. These signals, and the responses to them, help maintain balance.
VESTIBULAR SYSTEM.: A complex organ located inside the inner ear that sends messages to the brain about movement and body position. Allows people to maintain their balance when moving by sensing changes in their direction and speed.
VILLI.: Tiny, finger-like projections that enable the small intestine to absorb nutrients from food.
VISUAL ACUITY.: The ability to distinguish details and shapes of objects.
VISUAL CORTEX.: The area of the brain responsible for receiving visual stimuli from the eyes and integrating it to form a composite picture of an object.
VITAMIN DEFICIENCY.: Abnormally low levels of a vitamin in the body.
VOLUNTARY MUSCLE.: A muscle under conscious control, such as arm and leg muscles.
VOLVULUS.: A twisted loop of bowel, causing obstruction.
VON WILLEBRAND FACTOR (VWF).: A protein found in the blood that is involved in the process of blood clotting.

W

WEYERS ACROFACIAL DYSOSTOSIS.: The condition resulting from a mutation of the same gene that shows mutation in Ellis–van Creveld syndrome. As is usually the case when comparing expressions of the same gene mutation, the single dose Weyers acrofacial dysostosis presents milder symptoms than the double dose Ellis-van Creveld syndrome.
WHIPPLE PROCEDURE.: Surgical removal of the pancreas and surrounding areas, including a portion of the small intestine, the duodenum.
WHITE BLOOD CELL.: A cell in the blood that helps fight infections.
WHITE MATTER.: A substance, composed primarily of myelin fibers, found in the brain and nervous system that protects nerves and allows messages to be sent to and from the brain and various parts of the body. Also called white substance.

WILSON DISEASE.: A rare hereditary disease marked by high levels of copper deposits in the brain and liver. It can cause psychiatric symptoms resembling schizophrenia.
WOLFFIAN DUCTS.: Structures in the embryo that develop into epididymides, vasa deferentia, and seminal vesicles in males.
WORD SALAD.: Speech that is so disorganized that it makes no linguistic or grammatical sense.
WORMIAN BONES.: A condition of the bones and cartilage in which growing bones are abnormally connected by thin string-like structures.

X

X CHROMOSOME.: One of the two sex chromosomes (the other is Y) containing genetic material that, among other things, determine a person's gender.
X-INACTIVATION.: A condition in which one of the X chromosomes of a female is suppressed, or "turned off," in favor of the other X chromosome. Preferential X-inactivation is a process in which one X chromosome is inactivated in all the cells of the body, in preference to the other X chromosome. Females with preferential X-inactivation express X-linked traits as if they are hemizygous rather than homozygous or heterozygous.
X-LINKED.: A gene carried on the X chromosome, one of the two sex chromosomes.
X-LINKED DOMINANT INHERITANCE.: The inheritance of a trait by the presence of a single gene on the X chromosome in a male or female, passed from an affected female who has the gene on one of her X chromosomes.
X-LINKED MENTAL RETARDATION.: Subaverage general intellectual functioning that originates during the developmental period and is associated with impairment in adaptive behavior. Pertains to genes on the X chromosome.
X-LINKED MUTATION.: An abnormal gene transmitted on the X chromosome.
X-LINKED RECESSIVE INHERITANCE.: The inheritance of a trait by the presence of a single gene on the X chromosome in a male, passed from a female who has the gene on one of her X chromosomes, who is referred to as an unaffected carrier.
X RAY.: A form of electromagnetic radiation with shorter wavelengths than normal light. X rays can penetrate most structures and are used in the diagnosis and treatment of diseases.
XANTHOMA.: Small, localized areas of fat deposition.

Z

ZYGOTE.: The result of the sperm successfully fertilizing the ovum. The zygote is a single cell that contains the genetic material of both the mother and the father.