AVPR2 and Down syndrome: Tolvaptan (TLV, Samsca® or Jinarc®) is recognized as an oral aquaretic agent that functions as a selective, competitive antagonist of the vasopressin V2 receptor, used to treat different types of hyponatremia associated with varying pathological conditions, such as congestive heart failure, cirrhosis, or the syndrome of inappropriate antidiuretic hormone [61,62,63,64].