The PHEX a 749 amino acid protein that putatively consists of an intracellular, transmembrane and extracellular domain. PHEX mutations have been observed in 60-80% of hypophosphatemic rickets patients. The PHEX protein, which is a single-pass membrane protein, is also designated HYP, X-linked hypophosphatemia protein or metalloendopeptidase homolog PEX. PHEX plays an active role in bone and dentin mineralization and renal phosphate re-absorption. X-linked hypophosphatemic rickets, also designated HYP, is an X-linked dominant disorder characterized by impaired phosphate uptake in the kidney, which is likely to be caused by abnormal regulation of sodium phosphate cotransport in the proximal tubules. Clinical manifestations include skeletal deformities, growth failure, craniosynostosis, paravertebral calcifications, pseudofractures in lower extremities, and muscular hypotonia with onset in early childhood.