Hyponatremia is an infrequent but significant side effect known to occur during the administration of some psychiatric medications such as aripiprazole, causing the syndrome of inappropriate antidiuretic hormone secretion (SIADH), in which water homeostasis is disrupted by a continuous secretion of antidiuretic hormone (ADH), even when there are no exogenous or endogenous triggers [85,87]. The gene discussed is AVP; the disease is Down syndrome.