Genetic disorders in which vitamin D is not normally metabolized can lead not only to excessive production of active vitamin D and hypercalcemia or kidney stones or nephrocalcinosis [39, 40], as noted above, but also to excessive metabolism of vitamin D by activation of cytochrome P450 3A4 (CYP3A4) resulting in rickets or osteomalacia [39, 41–43]. The gene discussed is CYP3A4; the disease is osteomalacia.