The serotonin transporter (SERT) modulates the concentration of serotonin in extracellular fluids. Given this essential role,
genetic variability in SERT is of considerable interest in elucidating disorders of serotoninergic activity. Genetic disturbances
within the chromosome 17q region where SERT is located have been mapped and may be associated with a variety of disorders,
including autism, attention deficit-hyperactivity disorder, bipolar disorder, and Tourette’s syndrome. Studies of knockout
mice, moreover, suggest SERT as a determinant of additional clinical conditions, ranging from irritable bowel syndrome to
obesity. The association of certain polymorphisms with poorer therapeutic responses to SERT antagonists, including more frequent
serious side effects, also has important implications for the treatment of emotional disorders.