The molecular background to hypophosphataemic rickets.

Bone mineral loss disorders are major, worldwide health concerns, and can be familial, idiopathic, oncogenic, dietary, or hormonal. The mechanisms controlling bone integrity are complex. Extensive research has been directed towards the characterisation of the key factors involved in bone mineral regulation and two specific bone diseases, X-linked hypophosphataemic rickets (HYP) and oncogenic hypophosphataemic osteomalacia (OHO). The primary defect in HYP is a defective zinc metalloendopeptidase (PHEX), and a new candidate glycoprotein (MEPE) has been proposed as the phosphaturic factor released by OHO tumours. 6 Both diseases cause severe changes in bone morphology and have an overlapping pathophysiology. This review will discuss the recent molecular advances in our understanding of the role of the kidney and other organs in bone mineral homeostasis, with emphasis on X-linked hypophosphataemic rickets and tumour osteomalacia.