Previous observational studies have demonstrated that the circulating concentration of FGF23 is related to heart failure (HF) (22, 29, 35–45), and this association appears to be stronger in patients with CKD (36, 37, 44, 46), but is not affected by adjustment for kidney function (22, 35, 37, 39, 41–44). The gene discussed is FGF23; the disease is hydrops fetalis.