Genetic evidence that the human CYP2R1 enzyme is a key vitamin D 25-hydroxylase

doi:10.1073/pnas.0402490101

Genetic evidence that the human CYP2R1 enzyme is a key vitamin D 25-hydroxylase

Departments of ^*Molecular Genetics and ^§Pharmacology and the ^¶Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390; ^†Division of Pediatrics, Children's Hospital, Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195; and ^‡Department of Medicine, Medical University of South Carolina, Strom Thurmond Research Building, 114 Doughty Street, Charleston, SC 29425

Communicated by Jean D. Wilson, University of Texas Southwestern Medical Center, Dallas, TX, April 8, 2004 (received for review February 16, 2004)

Abstract

The synthesis of bioactive vitamin D requires hydroxylation at the 1α and 25 positions by cytochrome P450 enzymes in the kidney and liver, respectively. The mitochondrial enzyme CYP27B1 catalyzes 1α-hydroxylation in the kidney but the identity of the hepatic 25-hydroxylase has remained unclear for >30 years. We previously identified the microsomal CYP2R1 protein as a potential candidate for the liver vitamin D 25-hydroxylase based on the enzyme's biochemical properties, conservation, and expression pattern. Here, we report a molecular analysis of a patient with low circulating levels of 25-hydroxyvitamin D and classic symptoms of vitamin D deficiency. This individual was found to be homozygous for a transition mutation in exon 2 of the CYP2R1 gene on chromosome 11p15.2. The inherited mutation caused the substitution of a proline for an evolutionarily conserved leucine at amino acid 99 in the CYP2R1 protein and eliminated vitamin D 25-hydroxylase enzyme activity. These data identify CYP2R1 as a biologically relevant vitamin D 25-hydroxylase and reveal the molecular basis of a human genetic disease, selective 25-hydroxyvitamin D deficiency.

Footnotes

↵ ∥ To whom correspondence should be addressed. E-mail: david.russell{at}utsouthwestern.edu.
Abbreviations: vitamin D₃, (3β,5Z,7E)-9,10-secocholesta-5,7,10(19)-trien-3-ol; vitamin D₂, (3β,5Z,7E,22E)-9,10-secoergosta-5,7,10(19),22-tetraen-3-ol; CYP, cytochrome P450; GAL4, galactose 4; VDR, vitamin D receptor; VDRE, vitamin D response element; TK, thymidine kinase; HEK, human embryonic kidney; LUC, luciferase.