CYP27B1 and chronic kidney disease: Patients with impaired renal function have reduced activity of 1α-hydroxylase (CYP27B1), therefore, nephrologists have been traditionally more prone to treat CKD patients with hypovitaminosis D using activated vitamin D or related analogs, including selective VDRA, paricalcitol, or non-selective VDRA such as calcitriol, alfacalcidol, doxercalciferol, 22-oxacalcitriol, and maxacalcitol [59].