Inactivating mutations in the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) cause X-linked hypophosphatemic rickets (OMIM 307800) [10], and loss of DMP1 activity results in autosomal-recessive hypophosphatemic rickets (OMIM 241520) [11], [13]. This evidence concerns the gene PHEX and autosomal recessive hypophosphatemic rickets.