Nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is a rare genetic disorder of water balance, closely resembling the far more frequent syndrome of inappropriate antidiuretic secretion (SIAD), and characterized by euvolemic hypotonic hyponatremia due to impaired free water excretion and undetectable or low plasma arginine vasopressin (AVP) levels. The disease is Monarch Disease Ontology id MONDO_0010356 (nephrogenic syndrome of inappropriate antidiuresis). Also known as: NSIAD, nephrogenic syndrome of inappropriate antidiuresis, X-linked recessive.