To our knowledge, this is the only region that has been studied in humans with respect to GDNF, although several studies have investigated the serum level of GDNF in MDD (Diniz et al. 2012a, b; Pallavi et al. 2013; Zhang et al. 2008) and under antidepressant treatment (Zhang et al. 2008). The gene discussed is GDNF; the disease is major depressive disorder.