MENTAL RETARDATION

The term "mental retardation" refers to persons with deficits in both their intellectual and adaptive (everyday) functioning. These individuals typically show IQ scores below 70, as well as difficulties in meeting the demands of everyday living, whether it be in communicating and socializing with others or attending to grooming and domestic chores. Mental retardation manifests itself in the developmental years, before age eighteen.

Anywhere from 1 to 3 percent of the population is estimated to be mentally retarded. The majority of these persons (about 85 percent), show mild levels of delay, with IQs ranging from 55 to 70. Approximately 10 percent show moderate delays, with IQs from 40 to 55. With proper supports, individuals with mild to moderate mental retardation successfully live and work in their communities, or in supervised settings such as group homes. The remainder of persons show severe to profound levels of mental retardation (IQs of 40 and below), and many of these individuals have sensory, motor, or medical problems that further complicate their care.

Mental retardation has multiple causes. Approximately 50 percent of persons with mental retardation do not have a clear-cut organic or biological cause for their delay. The low IQ of these persons is likely due to a combination of environmental and genetic factors. The other 50 percent of persons with mental retardation have a known biological etiology. These include prenatal causes such as genetic disorders or alcohol exposure in utero; perinatal causes such as premature birth; and postnatal causes such as head trauma and exposure to lead.

There are now over 750 known genetic disorders that cause mental retardation, accounting for about half of those with organic etiologies. Some of these can be screened for during pregnancy—including Down syndrome, the most common chromosomal cause of mental retardation. Other disorders include fragile X syndrome, Prader-Willi syndrome, and Williams syndrome. People with these and other syndromes often show distinctive personalities, behavioral problems, and intellectual strengths and weaknesses that can be used to guide their care.

Some organic causes of mental retardation can be prevented. As many as two in one thousand children are born with fetal alcohol syndrome, which is prevented by refraining from drinking alcohol during pregnancy. Babies born with phenylketonuria, or PKU, are placed on a special, phenylalanine-reduced diet, thereby avoiding the severe mental retardation that otherwise characterizes this disorder.

People with mental retardation are at higher risk than those in the general population for behavioral and psychiatric problems such as autism, hyperactivity, and self-injurious behaviors. Throughout the early to mid-1900s, many of these individuals, as well as those without behavioral problems, were placed in large institutions. Since the advent of deinstitutionalization in the 1960s, most children with mental retardation have been cared for by their families. To improve the quality of life for these children, the Americans with Disabilities Act and other federal legislation emphasize community inclusion and specialized services such as early intervention, special education, and school-to-work transition. Many individuals also benefit from occupational, physical, and speech-language therapies, as well as from programs that teach daily living skills. With proper support, most people with mental retardation successfully live, work, and play in their communities.

BIBLIOGRAPHY

Arc of the United States. "Information about Mental Retardation and Related Topics." Available at http://www.thearc.org.

Dykens, E. M. (2000). "Psychopathology in Children with Intellectual Disabilities." Journal of Child Psychology and Psychiatry 41:407–417.

Dykens, E. M.; Hodapp, R. M.; and Finucane, B. M. (2000). Genetics and Mental Retardation Syndromes: A New Look at Behavior and Intervention. Baltimore, MD: Paul H. Brookes.

Hodapp, R. M., and Dykens, E. M. (1996). "The Child with Mental Retardation." In Child Psychopathology, eds. E. J. Mash and R. A. Barkley. New York: Gilford Press.

King, B. H.; Hodapp, R. M.; and Dykens, E. M. (2000). "Mental Retardation." In Comprehensive Textbook of Psychiatry, 7th edition, eds. H. I. Kaplan and B. J. Sadock. New York: Williams & Wilkins.