Renal phosphate wasting disorders: clinical features and pathogenesis.

Rickets and osteomalacia are associated with hypophosphatemia in several disease states, including X-linked hypophosphatemic rickets, autosomal-dominant hypophosphatemic rickets, and tumor-induced osteomalacia. Recent advances in the understanding of these diseases include discovery of mutations in the genes encoding human phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX) and fibroblast growth factor 23 (FGF-23) and the finding of overproduction of FGF-23 and other proteins including matrix extracellular phosphoglycoprotein (MEPE) and frizzled-related protein 4 (FRP-4) in tumor-induced osteomalacia. Research is ongoing to better define how these proteins relate to each other and to the sodium-phosphate cotransporter in both normal and abnormal phosphate metabolism. New and improved therapies for disorders of phosphate metabolism, osteomalacia, and rickets will develop as our knowledge of phosphate metabolism grows.