DMP1 and hypophosphatemic rickets: Inactivating mutations in DMP1 and PHEX lead to XLH (X-linked hypophosphatemic rickets) and ARHR (autosomal recessive hypophosphatemic rickets), respectively, accompanying with increased serum FGF23 level.594,595 Both DMP1 and PHEX knockout mice exhibit hypophosphatemic rickets and increased FGF23 expression.594,596 Although PHEX is a peptidase expressed in the bone, it can inhibit the expression FGF23 without regulating FGF23 degradation.597