Although hyponatremia is considered to reflect the severity of HF [31], we did not find any correlation between hyponatremia and established indices of cardiac function like LVEF, NT-proBNP, and hs-TnT, which suggests that additional factors (e.g. water intake) are important for developing hyponatremia in HF patients. The gene discussed is NPPB; the disease is hydrops fetalis.