FGF23 and secondary hyperparathyroidism: α-Klotho deficiency is associated with progression and chronic complications in chronic kidney disease, including vascular calcification, cardiac hypertrophy, and secondary hyperparathyroidism; in particular, α-klotho deficiency induces resistance to fibroblast growth factor-23 and predisposition to hyperphosphatemia, which represents a critical feature of chronic kidney disease [1].