In recent years, there has been growing evidence to show that the brain-derived neurotrophic factor (BDNF)/TrKB pathway can modulate serotonin (5-hydroxytryptamine; 5-HT) and other neurotransmitters, and this pathway has been implicated in the pathophysiology and treatment of depression and anxiety (14). The gene discussed is NTRK2; the disease is depressive disorder.