A CASE - CONTROL FAMILY HISTORY STUDY OF AUTISM

Family history data on 99 autistic and 36 Down's syndrome probands are reported. They confirmed a raised familial loading for both autism an d more broadly defined pervasive developmental disorders in siblings ( 2.9% and 2.9%, respectively, vs 0% in the Down's group) and also evide nce for the familial aggregation of a lesser variant of autism, compri sing more subtle communication/social impairments or stereotypic behav iours, but not mental retardation alone. Between 12.4 and 20.4% of the autism siblings and 1.6% and 3.2% of the Down's siblings exhibited th is lesser variant, depending on the stringency of its definition. Amon gst autistic probands with speech, various features of their disorder (increased number of autistic symptoms; reduced verbal and performance ability) as well as a history of obstetric complications, indexed an elevation in familial loading. No such association was seen in the pro bands without speech, even though familial loading for the lesser vari ant in this subgroup, was significantly higher than in the Down's cont rols. The findings suggest that the autism phenotype extends beyond au tism as traditionally diagnosed; that aetiology involves several genes ; that autism is genetically heterogeneous; and that obstetric abnorma lities in autistic subjects may derive from abnormality in the foetus.