Autism spectrum disorders (ASD) are defined by impairments in reciprocal social interaction, communication, and the presence of stereotyped repetitive behaviors and/or highly restricted interests. A genetic contribution is well established from twin studies (Bailey et al., 1995; Lichtenstein et al., 2010) in which the very large difference between the monozygotic and dizygotic concordance rates is consistent with the contribution of de novo mutation and/or complex inheritance. In addition, the over-representation of ASD in monogenic developmental disorders (Klauck et al., 1997; Smalley et al., 1992), gene discovery in families with Mendelian forms of the syndrome (Morrow et al., 2008; Strauss et al., 2006), and long-standing evidence for an increased burden of gross chromosomal abnormalities (Bugge et al., 2000; Veenstra-Vanderweele et al., 2004; Vorstman et al., 2006; Wassink et al., 2001) all point to the importance of genetic risks.
