Mental retardation is a term used to describe individuals who exhibit subaverage intelligence, as measured by a standardized intelligence quotient (IQ) test, and deficits in adaptive functions (ie, activities of daily living). The etiologic factors associated with the development of mental retardation have been identified as genetic (eg, chromosomal and inherited conditions), developmental (eg, prenatal exposure to toxins and infections), and acquired syndromes (eg, perinatal trauma and sociocultural factors). For example, although Down syndrome (also known as trisomy 21) is a general medical condition, it is a form of mental retardation caused by the abnormality. Phenylketonuria is a genetic, metabolic disorder characterized by the inability to convert phenylalanine to tyrosine. Abnormal accumulation of chemicals interferes with brain development and, if untreated, can result in mental retardation. Mental retardation has also occurred when fetuses were exposed to radiation, syphilis, oxygen deprivation, poor maternal nutrition, alcohol, or drugs in utero.
In approximately two thirds of all individuals with mental retardation, the probable cause can be identified. It is not unusual for a comorbid mental disorder to be present (Sadock & Sadock, 2003).
The past 2 decades have seen enormous changes in services for children with learning and developmental difficulties such as mental retardation, who are referred to by the general public as â€œmentally or developmentally challenged.â€ Although onset occurs before the age of 18 years, the incidence is difficult to calculate because mental retardation sometimes goes unrecognized until middle childhood. Its prevalence rate has been estimated at approximately 1% of the population, with the highest incidence in school-age children peaking at ages 10 to 14. It occurs about 1Â½ times more frequently among men than among women. The trend toward...