The BDNF/TrkB system has been implicated in the pathophysiology of a number of psychiatric disorders, such as schizophrenia (Autry and Monteggia, 2012), depression (Autry and Monteggia, 2012), and PTSD (Grassi-Oliveira et al., 2008; Angelucci et al., 2014; Dretsch et al., 2016). The gene discussed is NTRK2; the disease is major depressive disorder.