Entheses from mice lacking vitamin D 1α-hydroxylase (Cyp27b1) (C–/–) had a similar enthesopathy to Hyp mice, whereas deletion of Fgf23 in Hyp mice prevented enthesopathy, and deletion of both Cyp27b1 and Fgf23 in mice resulted in enthesopathy, demonstrating that the impaired 1,25D action due to high FGF23 levels underlies XLH enthesopathy development. This evidence concerns the gene CYP27B1 and enthesopathy.