In NMOSD patients, syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the most common cause of hyponatremia, accounting for about 14.6%–16% (Iorio et al., 2011; Pu et al., 2015).The hypothalamus is the area of high expression of AQP4. The gene discussed is AQP4; the disease is Hyponatremia.