Familial heterogeneity in infantile autism

Abstract

The incidence of autism and cognitive disability was assessed in the biological siblings of 29 autistic probands subdivided on the basis of IQ. A significant clustering of autism and nonspecific intellectual retardation was found in the siblings of severely retarded autistic probands which was not present in the siblings of our higherfunctioning autistic sample. These findings suggest that there may be etiological differences in autism, depending on the degree of associated mental retardation.