title: Prevalence of the fragile-X syndrome in mentally retarded boys in a Swedish county.
abstract: In an etiological study of an unselected series of mentally retarded children (IQ less than 70) born 1959-1970 in a northern Swedish county, 12 of 205 boys (5.9%) were found to have a fragile site on the distal end of the C-chromosome (fra (X) (q27]. The incidence of the fra (X) syndrome was calculated to be 1:1500 boys in this county. If this is true for the whole of Sweden, 30-40 new cases of the fra (X) syndrome should be born yearly in Sweden. This must be considered a minimum figure, since a certain proportion of individuals with fra (X) are not observed in groups of mentally retarded patients. Next to trisomy 21, the fragile X syndrome is the most common specific cause of mental retardation among mentally retarded boys in Sweden.
mesh_terms: D000293:Adolescent; D000328:Adult; D004812:Epidemiologic Methods; D005600:Fragile X Syndrome / Q000453:epidemiology*; D005820:Genetic Testing; D006801:Humans; D008607:Intellectual Disability / Q000209:etiology / Q000235:genetics*; D008297:Male; D012729:Sex Chromosome Aberrations / Q000453:epidemiology*; D013548:Sweden