To investigate whether ZK modifications are CYP24A1 dependent, ZK activities were determined in fibroblasts from an adult patient with hypercalcemia carrying CYP24A1 loss-of-function mutations18 (FB-CYP) and in the human fibroblastic cell line FB-78919, used as control. The gene discussed is CYP24A1; the disease is Hypercalcemia.