Fibroblast growth factor 23 as a phosphotropic hormone and beyond.

Fibroblast growth factor 23 (FGF23) is produced by bone and reduces serum phosphate by inhibiting proximal tubular phosphate reabsorption and intestinal phosphate absorption. Excess actions of FGF23 cause several kinds of hypophosphatemic rickets/osteomalacia while deficient actions of FGF23 result in hyperphosphatemic tumoral calcinosis. In addition, FGF23 has been shown to prevent the development of hyperphosphatemia during the progression of chronic kidney disease-mineral and bone disorder. Epidemiological studies have indicated that high FGF23 levels are associated with unfavorable events including higher mortality, cardiovascular events, progression of CKD and fracture; however, these associations are not observed unequivocally and it is not evident why they are present. While FGF23 has been shown to be a hormone that regulates phosphate metabolism, it remains to be established whether FGF23 has roles other than regulating mineral homeostasis.