The severe hypercalcemia and nephrocalcinosis in children and adults with a loss of function mutation of this gene (61, 62), which corroborated the phenotype of the CYP24A1 null mouse (63), strongly supports the clinical significance of calcitriol induction of CYP24A1 in vitamin D responsive tissues. The gene discussed is CYP24A1; the disease is Hypercalcemia.