title: Epidemiology of severe mental retardation in children: community studies.
abstract: Twenty-seven community studies of severe mental retardation, defined as IQ less than 50, were reviewed. The prevalence rate of this condition was about 4 per 1000 in older children; the rate was somewhat higher in males but did not vary by social class. About one-half of severely retarded children had significant associated handicaps. The cause of most cases of severe mental retardation is not known, but Down's syndrome accounted for one-sixth to one-third of cases and a small percentage were due to other chromosomal abnormalities, metabolic diseases, or infection.
mesh_terms: D000015:Abnormalities, Multiple; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D002675:Child, Preschool; D002869:Chromosome Aberrations / Q000150:complications; D025063:Chromosome Disorders; D004314:Down Syndrome / Q000150:complications; D004812:Epidemiologic Methods; D005060:Europe; D005260:Female; D006801:Humans; D007239:Infections / Q000150:complications; D008607:Intellectual Disability / Q000150:complications / Q000453:epidemiology* / Q000209:etiology; D007360:Intelligence; D008297:Male; D008659:Metabolic Diseases / Q000150:complications; D012306:Risk; D012424:Rural Population; D012737:Sex Factors; D012923:Social Class; D014481:United States; D014505:Urban Population