To rule out inappropriate antidiuretic hormone secretion as the cause of hyponatremia, we checked the cortisol and thyroid function, which showed low cortisol level (ante meridiem cortisol: 2.7 μg/dL) with normal adrenocorticotropic hormone (ACTH: 40.30 pg/mL), low free thyroxine 4 (0.40 ng/dL), low free T3 (1.56 pg/mL), elevated thyroid peroxidase antibody (803.5 IU/mL) and normal thyroid-stimulating hormone (TSH: 1.55 μIU/mL). The gene discussed is POMC; the disease is Hyponatremia.