The results of case-control studies have been inconsistent. Two studies have reported an enrichment of rare CNVs in bipolar disorder (Priebe et al., 2011; Zhang et al., 2009a). In both studies, the observed effect was greatest in subjects with an early age-at-onset. However, the observed effects were still quite small (OR~1.5), and results from two other studies (Grozeva et al., 2010; McQuillin et al., 2011) did not support these findings. Notably, very few of the CNVs that contribute to risk for schizophrenia are also associated with bipolar disorder, the possible exceptions being microduplications of 16p11.2 (McCarthy et al., 2009) and microdeletions of 3q29 (Clayton-Smith et al., 2010; Malhotra et al., 2011), which have been reported in multiple cases (Table 1).
