Because both treatments attenuated Hyp enthesopathy despite dramatic increases in Fgf23 expression (15), these studies implicate impaired 1,25D action due to the high serum levels of FGF23 in XLH rather than direct effects of increased circulating FGF23 in the pathogenesis of XLH enthesopathy. The gene discussed is FGF23; the disease is enthesopathy.