CYP27B1 and vitamin D-dependent rickets, type 1A: Mutations in CYP27B1 cause a disease known as pseudovitamin D–deficiency rickets or type 1A vitamin D-dependent rickets (23); both the renal and extrarenal CYP27B1 have the same sequence, but their differences in regulation occur because of differences in tissue-specific multicomponent control modules within the regulatory regions of the gene.