FGF-23 may be more than just a regulator of renal phosphate handling.(66) In addition to hypophosphatemic rickets, FGF-23 is elevated in osteocytes in patients with chronic kidney disease (CKD).(67) Progression in CKD is associated with elevated FGF-23.(68) Also, increased death with cardiovascular disease is associated with elevated FGF-23, as is calcification.(69) It will be important to determine if this osteocyte-derived factor has a direct effect on tissues other than the kidney. This evidence concerns the gene FGF23 and chronic kidney disease.