CYP27A1 and vitamin D deficiency: It is now recognized that 1,25-dihydroxy vitamin D deficiency in patients with NDD-CKD can be exacerbated by sustained increases in fibroblast growth factor 23 (FGF23), which directly suppress cytochrome P450 (CYP)27 (1-alpha-hydroxylase) and stimulate catabolic CYP24 (24-hydroxlase) [30–32].