Considering the role of BDNF and its related receptors in neural plasticity and structural changes, along with the fact that depression and antidepressants exert opposing effects on BDNF expression and TrkB function, it is evident that BDNF may play a pivotal role in the pathophysiology of MDD and the mechanism of action of antidepressant drugs. The gene discussed is BDNF; the disease is major depressive disorder.