Mutations of the activating enzymes CYP2R1 and CYP27B1 cause lack of normal 1,25-(OH)<sub>2</sub>D<sub>3</sub> synthesis and result in rickets whereas mutations of the inactivating enzyme CYP24A1 cause build-up of excess 1,25-(OH)<sub>2</sub>D<sub>3</sub> and result in hypercalcemia, nephrolithiasis, and nephrocalcinosis.