Phosphate-regulating neutral endopeptidase, X-linked also known as phosphate-regulating gene with homologies to endopeptidases on the X chromosome or metalloendopeptidase homolog PEX is an enzyme that in humans is encoded by the PHEXgene. This gene contains 18 exons and is located on the X chromosome.
The protein encoded by this gene is a transmembrane endopeptidase that belongs to the type II integral membrane zinc-dependent endopeptidase family. The protein is thought to be involved in bone and dentin mineralization and renal phosphate reabsorption. The bone and dentin protein osteopontin (OPN) which inhibits mineralization in the skeleton and in teeth is a substrate for PHEX. In the absence of functional PHEX in the mouse model (Hyp) of X-linked hypophosphatemia (XLH), and in human XLH where PHEX activity is decreased or absent, in addition to renal phosphate wasting, osteopontin and osteopontin fragments accumulate in bone and teeth and may contribute locally to the osteomalacia characteristic of XLH/HYP. XLH patients have soft and deformed skeletons and soft teeth that easily become infected.
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