CYP27B1 and enthesopathy: To identify the relative roles of impaired 1,25D action and enhanced FGF23 action (both of which are due to high circulating levels of FGF23), and the PHEX mutation in enthesopathy development, we analyzed entheses from mice lacking Cyp27b1, Fgf23, or both; and from Hyp mice lacking Cyp27b1, Fgf23, or both.