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 PHEX gene. It is mapped to Xp22.11. 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. Mutations in this gene cause X-linked hypophosphatemic rickets. Alternative splicing results in multiple transcript variants.