The serotonin transporter (SLC6A4) regulates synaptic levels of serotonin, a neurotransmitter involved in the regulation of mood, appetite, and impulse control. Reflecting these diverse actions, serotonin-specific reuptake inhibitors are the most commonly prescribed category of medications for mental illness. The serotonin transporter gene SLC6A4 has a common variable number tandem repeat (VNTR) in its promoter region (HTTLPR) (Fig. 8) that is the most frequently studied locus in psychiatric genetics.
