This, however, does not appear to be the case here as four of the five included studies (Hauck et al., 2010; Maina et al., 2010; Bonne et al., 2011; Wang et al., 2011) found that the presence of past and/ or current depression did not have a significant effect, while the fifth study found BDNF levels were in fact elevated in patients with MDD (dos Santos et al., 2011). The gene discussed is BDNF; the disease is major depressive disorder.