The effect of de novo CNV on age at onset in bipolar disorder was nominally significant. These preliminary findings and similar results from previous studies (Priebe et al., 2011 and Zhang et al., 2009) suggest that individuals with an early onset of mania might constitute a subclass of bipolar disorder in which there is a greater contribution from rare alleles of large effect. Also consistent with this notion is a previous study (Grigoroiu-Serbanescu et al., 2001), which found that segregation of early-onset BD in families was consistent with major gene effects, while familial segregation of late-onset BD was consistent with a multifactorial etiology.
