FGF23 and Marchiafava-Bignami disease: In response to declining kidney function, fibroblast growth factor 23 (FGF-23) production increases to induce phosphaturia in order to maintain normal phosphate levels, thereby reducing active vitamin D synthesis, leading to reduced calcium absorption, secondary hyperparathyroidism, and increased bone resorption, which ultimately results in CKD-MBD [2–4].