The serotonin transporter (SERT), which transports excessive serotonin from the synapse cleft to pre-synapse neurons, is important in terms of its antidepressant effects6 and several serotonin-related activities7, and altered SERT availability has been observed in major depressive disorder (MDD) and other anxiety disorders. The gene discussed is SLC6A4; the disease is major depressive disorder.