Laboratory tests at presentation also showed a urine osmolarity of 697 mOsm/L and urine Na of 40 mmol/L.<h4>Diagnoses</h4>The presenting concerns were consistent with syndrome of inappropriate antidiuretic hormone secretion (SIADH) manifesting as extreme, yet mildly symptomatic hyponatremia. The gene discussed is AVP; the disease is Hyponatremia.