Twin studies have confirmed that substantial genetic effects are shared between neuroticism and both anxiety and depression, and to a lesser extent, extraversion with depression (Kendler and Myers 2010; Middeldorp et al. 2005). Such findings provided the impetus for candidate gene studies to investigate pleiotropic gene effects on personality traits and psychological distress. For example, variants in GAD1 have been associated with neuroticism and anxiety/mood disorder measured in the same sample (Hettema et al. 2006). Genome-wide association studies (GWAS) have not systematically compared results of personality traits and mood. However, cross-disorder GWAS analysis has proved informative for uncovering pleiotropic effects on schizophrenia, bipolar disorder and major depressive disorder (Huang et al. 2010). The finding that genetic risk scores for neuroticism predicted major depressive disorder in an independent sample (Middeldorp et al. in press) is relevant to the present study, which hypothesizes that genetic prediction scores for stable personality traits will be related to mood states.
