It might be argued that major depression and anxiety disorders should not be considered “disease-like,” as these conditions are frequently accompanied by long-standing personality vulnerabilities (Bienvenu et al., 2004, Bienvenu et al., 2009, Roth et al., 1972). Major depression is likely a heterogeneous condition, including a more disease-like “endogenous” form and a less disease-like “neurotic” form (Roth, 2001, Shorter, 2009). Though some studies suggest that endogenous features are associated with higher heritability (Leckman et al., 1984a, Leckman et al., 1984b, McGuffin et al., 1996), aspects of depressive illness that appear particularly salient for heritability include the related features recurrence, early onset, and perhaps short duration (Kendler et al., 2007). When adjusted for the latter features, endogenous symptoms do not appear to uniquely predict heritability (Kendler et al., 1994, McGuffin et al., 1996, Weissman et al., 1986). In addition, the presence of comorbid anxiety disorders appears to increase, rather than decrease, the heritability of depressive illness (Kendler et al., 1994, Weissman et al., 1986).
