AVP and Postural instability: The congenital form of nephrogenic diabetes insipidus (NDI), a rare inherited disorder, is characterized by insensitivity of the distal nephron to the antidiuretic action of arginine-vasopressin (AVP) and the reduced ability of the kidney to concentrate the urine, leading to severe dehydration and electrolyte imbalance (hypernatremia and hyperchloremia) (1).