A family genetic study of autism associated with profound mental retardation

We sought to determine if the family loading for either the broader autism phenotype or for cognitive impairment differed according to whether or not autism was accompanied by severe mental retardation. The sample comprised 4 7 probands with autism meeting ICD-IO criteria, as assessed by the Autism D iagnostic Interview and the Autism Diagnostic Observation Schedule. Family history interview and findings were compared with those for the higher IQ a utism and Down syndrome samples in the Bolton et al. (1994) study. The fami lial loading for autism and for the broader phenotype was closely comparabl e to that in the study of higher IQ autism, and different from that for Dow n syndrome. The family loading for scholastic achievement difficulties was slightly, but significantly, higher when autism was accompanied by severe r etardation.