Approach to the treatment of the infant with hyponatremia.

Hyponatremia is an electrolyte abnormality that occurs in infancy due to a variety of inherited and acquired disorders. Infants with hyponatremia can present with neurologic symptoms such as vomiting, weakness, and seizures. Common causes of hyponatremia in the infant population are excess ingestion or administration of hypotonic fluids and excessive gastrointestinal salt loss. Hyponatremia in infancy also can be a sign of less common disorders, such as mineralocorticoid deficiency or resistance, and disregulation of arginine vasopressin with impaired free-water removal. Treatment of infants with hyponatremia is dependent on the severity of symptoms and the cause of hyponatremia. In nephrogenic syndrome of inappropriate antidiuresis (NSIAD), fluid retention is due to a gain-of-function mutation in the arginine vasopressin receptor 2 (AVPR2) gene leading to low arginine vasopressin levels. We describe the case of an infant with hyponatremia due to NSIAD, whose mother also has a known mutation in the AVPR2 gene. We report the approach to the treatment of hyponatremia and its unique challenges in infancy.