The observed rate of de novo CNVs in cases of bipolar disorder or schizophrenia with a positive family history of mental illness was similar to the rate in sporadic cases. These results contrast with earlier findings by our group and others in autism (Marshall et al., 2008 and Sebat et al., 2007) and schizophrenia (Xu et al., 2008) documenting a higher rate of CNVs in sporadic cases as compared with subjects who have a positive family history. These early observations have not been universally replicated (Kirov et al., 2011 and Pinto et al., 2010). The reason for the inconsistency is not clear. Possibly, the initial findings were incorrect. Alternatively, variation in the observed effect could occur by chance or it could potentially be explained by methodological differences between cohorts in how mental illness in first-degree relatives is ascertained.
