X-linked hypophosphatemic rickets (XLH) is the most common inherited form of rickets, caused by mutations in the PHEX gene that lead to excessive production of fibroblast growth factor 23 (FGF23).238 This hormone reduces phosphate reabsorption in the kidneys, resulting in chronic hypophosphatemia and impaired bone mineralization. Here, FGF23 is linked to rickets.