Hyp mice and XLH patients are characterized by loss-of-function mutations in PHEX (phosphate-regulating gene with homologies to endopeptidases on the X-chromosome), leading to impaired bone mineralization and subsequently increased biosynthesis of Fgf23 (Liu et al, 2003; Barros et al, 2013). Here, FGF23 is linked to X-linked hypophosphatemia.