Parents in the CATSS sample were interviewed with the Autism—Tics, AD/HD, and other Comorbidities inventory, a telephone interview designed for large-scale epidemiological research in neuropsychiatry (55). This measure was used in the current study because it assesses social functioning in great detail. Autism spectrum disorders (ASDs) are defined by current diagnostic criteria as being characterized by a triad of features: social impairments, communication impairments, and restricted repetitive behaviors and interests (DSM-IV), and thus there are different modules in A-TAC for these domains (60). A recent study from the CATSS-project showed that these domains are correlated, but have different genetic etiologies (61). Here we used A-TAC scores comprising all autism related A-TAC items (rather than dichotomous scales or scales based only on DSM-IV items) for the three domains separately as well as the A-TAC total autism spectrum score (60), because these measures had most variability and therefore provide most power to detect genetic effects in association analyses.
