Alternative approaches that focus on rare genetic variants are needed. One genetic approach that has been used effectively to overcome some of the problems of heterogeneity is the genome-wide analysis of rare copy-number variants (CNVs). Studies from our group (McCarthy et al., 2009, Sebat et al., 2007, Vacic et al., 2011 and Walsh et al., 2008) and from multiple independent groups (International Schizophrenia Consortium, 2008, Pinto et al., 2010, Stefansson et al., 2008 and Xu et al., 2008) have now firmly established that rare CNVs contribute to genetic risk for schizophrenia (SCZ) and autism spectrum disorder (ASD) and, in particular, that spontaneous (de novo) CNVs are important risk factors in the sporadic form of these disorders (Levy et al., 2011, Marshall et al., 2008, Sanders et al., 2011, Sebat et al., 2007 and Xu et al., 2008).
