FGF23 and Marchiafava-Bignami disease: In this study, accumulation of Pi, exhaustion of Ca, and excessive secretion of i-PTH in serum were observed in the 5/6 Nx model rats at the eighth week of the experiment, and the variation trend was consistent with that observed in CKD–MBD patients; elevation of serum FGF23 levels, which corresponded with increases in Pi and i-PTH levels, was also observed in the 5/6 Nx model rats.