Apparent Manifesting Heterozygosity in P450 Oxidoreductase Deficiency and Its Effect on Coexisting 21-Hydroxylase Deficiency

Scott, R.; Gomes, Larissa; Huang, Ningwu; Vliet, Guy Van; Miller, Walter L.

doi:10.1210/jc.2006-2345

Cited by 69 publications

(52 citation statements)

References 34 publications

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“…To identify POR amino acid sequence variations in the normal population, we sequenced the 15 protein-coding exons and at least 50 bp of each intron's splice donor and splice acceptor site adjacent to each exon from 842 individuals. To identify potential regulatory variants or splicing variants, we also sequenced the first untranslated exon 1U, which is 38.8 kb upstream from protein-coding exon 1 (15) and 274 bp of DNA 5Ј to exon 1U, in 701 of these 842 individuals. Approximately 5,655 bp of DNA were sequenced in each individual; the data can be found at www.pharmgkb.org.…”

Section: Resultsmentioning

confidence: 99%

“…Subjects identified themselves as African American, Caucasian American, Chinese American, or Mexican American by having all four grandparents of the stated ethnicity. DNA was sequenced as described (8,15). Primers (SI Table 5) were designed by using Primer3 (http:// frodo.wi.mit.edu/cgi-bin/primer3/primer3www.cgi) to span the first untranslated exon (exon 1U), 274 bp of 5Ј flanking DNA, the 15 protein-coding exons and at least 100 bp of intronic DNA adjacent to each exon.…”

Section: Methodsmentioning

confidence: 99%

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Genetics of P450 oxidoreductase: Sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

Huang¹,

Agrawal²,

Giacomini

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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P450 oxidoreductase (POR) is an electron-donating flavoprotein required for the activity of all microsomal cytochrome P450 enzymes. We sequenced 5,655 bp of the POR gene in a representative population of 842 healthy unrelated individuals in four ethnic groups: 218 African Americans, 260 Caucasian Americans, 179 Chinese Americans, and 185 Mexican Americans. One hundred forty SNPs were detected, of which 43 were found in >1% of alleles. Twelve SNPs were in the POR promoter region. Fifteen of 32 exonic variations altered the POR amino acid sequence; 13 of these 15 are previously undescribed missense variations. We found eight indels, only one of which was in the coding region. A previously described variant, A503V, was found on 27.9% of all alleles with some ethnic predilection (19.1% in African Americans, 26.4% in Caucasian Americans, 36.7% Chinese Americans, and 31.0% in Mexican Americans). We built cDNA expression vectors for the 13 previously undescribed missense variants, expressed each protein lacking 27 N-terminal residues in Escherichia coli, and assayed the apparent K m and Vmax of each in four assays: reduction of cytochrome c, oxidation of NADPH, 17␣-hydroxylase activity of P450c17, and 17,20 lyase activity of P450c17. The catalytic activities of several missense mutants differed substantially in these assays, indicating that each POR mutant must be assayed separately with each potential target P450 enzyme. The activity of A503V was reduced to a modest but statistically significant degree in all four assays, suggesting that it may play an important role in interindividual variation in drug response.cytochrome P450 ͉ drug metabolism ͉ electron transfer ͉ pharmacogenomics ͉ steroidogenesis P 450 oxidoreductase (POR) is a single protein containing both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) moieties that transfers electrons from NADPH to microsomal (type II) cytochrome P450 enzymes (for review, see ref. 1) (Fig. 1). Cytochrome P450 enzymes (http://drnelson.utmem.edu/ CytochromeP450.html) are heme-containing proteins that catalyze a broad range of oxidative reactions. The human genome contains 57 genes for cytochrome P450 enzymes; 7 encode Type I (mitochondrial) P450s and 50 encode Type II P450s, found in the endoplasmic reticulum (2). Among the 50 human microsomal P450 enzymes, approximately 20 are involved in the biosynthesis of steroids, sterols, fatty acids, and eicosanoids, approximately 15 participate in hepatic drug metabolism, and approximately 15 are ''orphan'' P450 enzymes whose catalytic roles are unclear (3).POR transfers electrons to three steroidogenic enzymes: P450c17 (17␣-hydroxylase/17,20 lyase), P450c21 (21-hydroxylase), and P450aro (aromatase) (4). Individuals with POR deficiency have a broad range of steroidogenic disorders, extending from infants with ambiguous genitalia and skeletal malformations to women with the polycystic ovary syndrome (5-8). Finding severe POR mutations in human patients was unexpected, because POR knockout mice die during embryonic devel...

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Genetics of P450 oxidoreductase: Sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

Huang¹,

Agrawal²,

Giacomini

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

185

176

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“…The human gene was identified on chromosome 7q11.2 as part of the Human Genome Project. The gene consists of 15 protein-coding exons spanning 32 kb (named exons 1–15), but it also has a non-coding exon (termed exon 1U) located 38 kb upstream [7]. …”

Section: P450 Enzymes and Pormentioning

confidence: 99%

Genetic and Clinical Features of P450 Oxidoreductase Deficiency

2008

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P450 oxidoreductase (POR) deficiency is an autosomal recessive disorder of steroidogenesis with multiple clinical manifestations. POR is the electron donor for all microsomal P450 enzymes, including the three steroidogenic enzymes P450c17 (17α-hydroxylase/17,20-lyase), P450c21 (21-hydroxylase), and P450aro (aromatase). Since the first description of POR mutations in 2004, about 50 patients have been reported. Serum steroid profiles indicate partial deficiencies in 21-hydroxylase, 17α-hydroxylase and 17,20-lyase. The 17-OH progesterone levels are elevated, as in 21-hydroxylase deficiency, while androgen levels are low; cortisol may be normal but is poorly responsive to adrenocorticotropic hormone. Most patients also have associated skeletal malfor- mations (craniosynostosis, radio-ulnar synostosis, midface hypoplasia, bowed femora) termed Antley-Bixler syndrome. Antley-Bixler syndrome with normal steroidogenesis is caused by autosomal dominant gain-of-function mutations in fibroblast growth factor receptor 2. Males with POR deficiency are often undervirilized, while females can be virilized. The prognosis for patients with POR deficiency appears to depend on the severity of the bony malformations and their timely treatment. The potential impact of POR mutations on drug metabolism by other hepatic P450 enzymes requires further investigation. Given the varied physical and biochemical phenotype of POR deficiency and the risk of adrenal insufficiency, clinicians should be alert to this potential diagnosis.

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“…P450 oxidoreductase (POR) can modify the phenotype of 21OHD (8). POR is a flavoprotein that transfers electrons from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to all microsomal P450s, including P450c21 (9).…”

Section: -Hydroxylase Deficiency (21ohd) Is Caused By Mutationsmentioning

confidence: 99%

“…Patients 9, 13, 14, and 17 had precocious pubarche and very high levels of 17OHP after ACTH stimulation. Patients 7,[8][9][10][11][12]15, and 16 are women with hirsutism, menstrual irregularities, and grossly elevated 17OHP after ACTH stimulation. Patients 13/14 and 15/16 are pairs of siblings who had mutations on only one allele.…”

Section: Patientsmentioning

confidence: 99%

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

Gomes

Huang

Agrawal

et al. 2008

The Journal of Clinical Endocrinology &Amp; Metabolism

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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. 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. Patients and Methods 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.

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Apparent Manifesting Heterozygosity in P450 Oxidoreductase Deficiency and Its Effect on Coexisting 21-Hydroxylase Deficiency

Abstract: Manifesting heterozygosity is a possible feature of POR deficiency and may ameliorate the findings in coexisting 21-hydroxylase deficiency.

Cited by 69 publications

References 34 publications

Genetics of P450 oxidoreductase: Sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

Genetics of P450 oxidoreductase: Sequence variation in 842 individuals of four ethnicities and activities of 15 missense mutations

Genetic and Clinical Features of P450 Oxidoreductase Deficiency

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

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