Core inclusion criteria were as follows: (1) Chronological age between 3 and 21 years of age; (2) Presumptive clinical diagnosis of autism; (3) Expert clinical determination of autism diagnosis using DSM-IV criteria supported by the Autism Diagnostic Interview (ADI-R) in the majority of cases and all available clinical information. The ADI-R is a semi-structured diagnostic interview which provides diagnostic algorithms for classification of autism (Autism Genetics Resource Exchange 2008). All ADI-R interviews were conducted by formally trained interviewers who have achieved reliability according to established methods. Thirty-eight individuals were missing an ADI-R. For those cases we implemented a best estimate procedure to determine a final diagnosis using all available information from the research record and data from other assessment procedures. This information was reviewed by a clinical panel led by an experienced clinical psychologist and included two other psychologists and a pediatric medical geneticist— all of whom were experienced in autism. Following review of case material the panel discussed the case until a consensus diagnosis was obtained. Only those cases in which a consensus diagnosis of autism was reached were
