X-linked hypophosphatemia (XLH) is a complex, rare, progressive, genetic disease characterized by loss-of-function mutations in the PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) gene (1–3), leading to increased serum/plasma levels of fibroblast growth factor 23 (FGF23) (3). Here, FGF23 is linked to X-linked hypophosphatemia.