Ca2+ homeostasis is altered in the majority of older adults, especially with chronic kidney disease (CKD), and is manifested predominantly as hypocalcemia, hyperphosphatemia, vitamin D deficiency, fibroblast growth factor-23 (FGF23) elevation (coupled with Klotho deficiency), and secondary hyperparathyroidism. The gene discussed is FGF23; the disease is vitamin D deficiency.