Subthreshold traits of the broad autistic spectrum are distributed across different subgroups in parents, but not siblings, of probands with autism.

Autism is a categorical developmental disorder characterized by impairment in socialization, communication, and by restricted and circumscribed interests. Several authors have described the presence of subthreshold autistic traits in the general population, pervasive developmental disorders representing the extreme end of their distribution. In this study, we explored the presence of autistic traits in siblings and parents of a proband with autism, and in siblings and parents of a normally developing child, using the previously validated self-report French Autism Quotient, an adaptation of the AQ developed by S. Baron-Cohen. Scores were distributed between two main factors, F1 corresponding to socialization and communication, F2 to imagination and rigidity. Here, we show that both parents and siblings of a child with autism have more symptomatic scores in the domains of communication and socialization. In addition, we show that in these families the parents, but not the siblings, are distributed across different subcategories, according to their scores for the F1 and F2 domains. We hypothesize that these different subgroups may correspond to different underlying genetic mechanisms.