FGF23 and X-linked hypophosphatemia: Increased FGF23 production in hereditary hypophosphatemic disorders is caused by loss-of-function mutations of bone factors involved in bone mineralization, including Pi-regulating gene with homologies to endopeptidase (PHEX) in XLH (15) and dentin matrix protein 1 (DMP1) in ARHR type 1 (ARHR1) (5, 16).