That is, several lines of evidence have suggested that the substitution of methionine for valine renders methionine carriers of the BDNF gene more vulnerable to anxiety, depression, and general psychiatric risk within the context of early life stress (Aguilera et al., 2009; Hayden et al., 2010; Kaufman et al., 2006), although others have failed to find such relationship (e.g., Willis-Owen et al., 2005). Here, BDNF is linked to major depressive disorder.