This Article Full Text Full Text (PDF) All Versions of this Article: 93/7/2913    most recent Author Manuscript (PDF) Author Manuscript (PDF) Author Manuscript (PDF) Submit a related Letter to the Editor Purchase Article View Shopping Cart Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Google Scholar Articles by Gomes, L. G. Articles by Miller, W. L. PubMed PubMed Citation Articles by Gomes, L. G. Articles by Miller, W. L. Related Collections Adrenal and Hypertension

The Common P450 Oxidoreductase Variant A503V Is Not a Modifier Gene for 21-Hydroxylase Deficiency

Department of Pediatrics (L.G.G., N.H., V.A., W.L.M.), University of California San Francisco, San Francisco, California 94143-0978; and Department of Endocrinology (L.G.G., B.B.M., T.A.S.S.B.), Hospital das Clinicas da Universidade de Sao Paulo, 05403-000 Sao Paulo, Brazil

Address all correspondence and requests for reprints to: Professor Walter L. Miller, Department of Pediatrics, HSE-1401, 513 Parnassus Avenue, University of California, San Francisco, San Francisco, California 94143-0978. E-mail: wlmlab{at}ucsf.edu.

Context: 21-hydroxylase deficiency (21OHD) is a common genetic disorder caused by mutations in the CYP21A2 gene, which encodes the adrenal 21-hydroxylase, microsomal P450c21. CYP21A2 gene mutations generally correlate well with impaired P450c21 enzymatic activity and the clinical findings in 21OHD, but occasional discrepancies between genotype and phenotype suggest the effects of modifier genes. Mutations in P450 oxidoreductase (POR), the protein that transfers electrons from reduced nicotinamide adenine dinucleotide phosphate to all microsomal P450s, can ameliorate the 21OHD phenotype and, therefore, could be a modifier gene.

Objectives: We sought to identify POR variants in patients with 21OHD having discordant phenotype and genotype, and to evaluate their effect on 21-hydroxylase activity.

Patients and Methods: We determined the CYP21A2 genotypes of 313 Brazilian patients with 21OHD and correlated the genotype and phenotype. The POR gene was sequenced in 17 patients with discordant genotype and phenotype. Wild-type and A503V POR, and P450c21 were expressed in bacteria and reconstituted in vitro. Activities were assayed by conversion of [¹⁴C]progesterone to deoxycorticosterone and [³H]17-hydroxyprogesterone to 11-deoxycortisol, and assessed by thin layer chromatography and phosphorimaging.

Results: The A503V POR variant was found in 10 of 30 alleles, the same ratio as in the normal population. There were no significant differences in Michaelis constant, maximum velocity and maximum velocity/Michaelis constant of 21-hydroxylase activity supported by wild-type and A503V POR.

Conclusion: The only POR missense polymorphism found in atypical 21OHD patients was A503V. Although A503V reduces P450c17 enzymatic activity, it does not influence P450c21 activity, indicating that POR A503V does not modify the 21OHD phenotype.