FGF23 and X-linked hypophosphatemia: In the presence of normal parathyroid and kidney function inappropriate high serum FGF-23 could result in urinary PO4 loss and hypophosphatemia such as X-linked dominant hypophosphatemic rickets (XLH), [41–44], autosomal dominant hypophosphatemic rickets [45, 46], Autosomal recessive hypophosphatemic rickets (ARHR) [47, 48] or Fibrous dysplasia (FD)/McCune–Albright syndrome [49].