FGF23 and chronic kidney disease: Hyperphosphatemia is a prominent feature of rare genetic conditions such as familial hyperphosphatemic tumoral calcinosis6, but most frequently encountered in patients with chronic kidney disease (CKD), which currently affects 20 Million Americans, and hyperphosphatemia and elevated blood fibroblast growth factor 23 (FGF23) levels are important predictors of mortality in these individuals7–9.