FGF23 and Marchiafava-Bignami disease: CKD–MBD is accompanied by systemic dysfunction of mineral and bone metabolism, such as abnormalities in serum calcium (Ca), phosphate (Pi), parathyroid hormone (PTH), vitamin D, and fibroblast growth factor 23 (FGF23) metabolism, as well as in bone turnover, mineralization, and volume (TMV).