Bone production of fibroblast growth factor 23 (FGF23) is increased in patients and animals with chronic kidney disease (CKD)1–3 and is associated with the development of left ventricular hypertrophy (LVH), heart failure, and mortality.1,2,4–7 Excess circulating FGF23 is the first major perturbation of mineral metabolism that occurs in CKD, however, the complex mechanisms that trigger elevations of FGF23 in CKD remain incompletely understood. This evidence concerns the gene FGF23 and chronic kidney disease.