Inactivating mutations of Phex, a phosphate-regulating endopeptidase, cause
hypophosphatemia and impaired mineralization in X-linked hypophosphatemia (XLH) and
its mouse homologue, Hyp. Because Phex is predominantly expressed in bone and cultured
osteoblasts from Hyp mice display an apparent intrinsic mineralization defect, it is thought
that reduced expression of Phex in mature osteoblasts is the primary cause of XLH. To test
this hypothesis, we studied both targeted expression of Phex to osteoblasts in vivo under the …