page_title: CYP2R1
section_title: Clinical significance
hierarchical_section_title: CYP2R1 / Clinical significance
caption_attribution_description: English: Enzymatic conversion of cholecalciferol to calcidiol by vitamin D 25-hydroxylase, a step in the biosynthesis of the active form of vitamin D3.
context_page_description: Vitamin D 25-hydroxylase also known as cytochrome P450 2R1 is an enzyme that in humans is encoded by the CYP2R1 gene.
context_section_description: An inherited mutation in the CYP2R1 gene which results in the substitution of a proline for a leucine residue at codon 99 eliminates the enzyme activity and is associated with low circulating levels of 25-hydroxyvitamin D and classic symptoms of vitamin D deficiency. The gene product which it encodes, vitamin D 25-hydroxylase, has therefore been proposed as the key enzyme in the conversion of cholecalciferol (vitamin D₃) to calcidiol. Calcidiol is subsequently converted by the action of 25-hydroxyvitamin D3 1-alpha-hydroxylase to calcitriol, the active form of vitamin D₃ that binds to the vitamin D receptor (VDR) which mediates most of the physiological actions of the vitamin.
caption: Conversion of cholecalciferol to calcidiol as catalyzed by CYP2R1.
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