The original 1397 families were collected from the 10 AGP sites in North America and Europe. For each site, the diagnosis of autism was based on the ADI-R and the Autism Diagnostic Observation Schedule or best clinical estimate (for details of the AGP data, see 3). Even though our linkage analyses used autism subphenotypes rather than the categorical diagnosis, to reduce genetic (locus) heterogeneity, families were included in the linkage analysis if they had at least two individuals diagnosed with ASD. Based on the results of Risi et al. (39), subjects were regarded as having ASD if they were 1) at/above the ADI-R autism cutoff on the social, communication, and repetitive behavior domains; 2) one point below the ADI-R autism cutoff on both the social and communication domains; 3) at/above the autism cutoff on the social domain but one or two points below the cutoff on the communication domain; or 4) at/above the autism cutoff on the communication domain but one or two points below the cutoff on the social domain. Details of the inclusion and exclusion criteria are provided in Supplement 1.
