Subjects diagnosed with autism spectrum disorders with both of their parents were recruited from clinics specializing in the diagnosis of Pervasive Developmental Disorders (PDD), readaptation centers, and specialized schools in the Montreal and Quebec City regions, Canada, as described 31. Subjects with ASD were diagnosed by child psychiatrists and psychologists expert in the evaluation of ASD. Evaluation based on the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria included the use of the Autism Diagnostic Interview-Revised (ADI-R)25 and the Autism Diagnostic Observation Schedule (ADOS)32. As an additional screening tool for the diagnosis of ASD, the Autism Screening Questionnaire, which is derived from the ADI-R, was completed 33. Furthermore, all proband medical charts were reviewed by a child psychiatrist expert in PDD to confirm their diagnosis and exclude subjects with any co-morbid disorders. Exclusion criteria were: (1) an estimated mental age < 18 months, (2) a diagnosis of Rett syndrome or Childhood Disintegrative Disorder and (3) evidence of any psychiatric and neurological conditions including: birth anoxia, rubella during pregnancy, fragile X syndrome, encephalitis, phenylketonuria, tuberous sclerosis, Tourette and West syndromes.
