Tolvaptan, which blocks arginine vasopressin (AVP) from binding to V2 receptors in the distal nephrons and thus restricts water reabsorption, is an ideal aquaretic drug for the treatment of hyponatremia in conditions associated with increased circulating levels of antidiuretic hormones, such as decompensated liver cirrhosis [8,9]. The gene discussed is AVP; the disease is Hyponatremia.