FGF23 and vitamin D-dependent rickets: Endo et al. evaluated the diagnostic value of intact FGF23 levels, using the Kainos assay in two studies in pediatric and adult Japanese patients with FGF23-mediated hypophosphatemia, including TIO, XLH, ARHR, ADHR, McCune-Albright syndrome/fibrous dysplasia in comparison to patients with non-FGF23-mediated forms of rickets (e.g., nutritional rickets, VDDR, Fanconi syndrome) [91, 92].