Diversity and Function of Mutations in P450 Oxidoreductase in Patients with Antley-Bixler Syndrome and Disordered Steroidogenesis

Abstract

P450 oxidoreductase (POR) is the obligatory flavoprotein intermediate that transfers electrons from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to all microsomal cytochrome P450 enzymes. Although mouse Por gene ablation causes embryonic lethality, POR missense mutations cause disordered steroidogenesis, ambiguous genitalia, and Antley-Bixler syndrome (ABS), which has also been attributed to fibroblast growth factor receptor 2 (FGFR2) mutations. We sequenced the POR gene and FGFR2 exons 8 and 10 in 32 individuals with ABS and/or hormonal findings that suggested POR deficiency. POR and FGFR2 mutations segregated completely. Fifteen patients carried POR mutations on both alleles, 4 carried mutations on only one allele, 10 carried FGFR2 or FGFR3 mutations, and 3 patients carried no mutations. The 34 affected POR alleles included 10 with A287P (all from whites) and 7 with R457H (four Japanese, one African, two whites); 17 of the 34 alleles carried 16 "private" mutations, including 9 missense and 7 frameshift mutations. These 11 missense mutations, plus 10 others found in databases or reported elsewhere, were recreated by site-directed mutagenesis and were assessed by four assays: reduction of cytochrome c, oxidation of NADPH, support of 17alpha-hydroxylase activity, and support of 17,20 lyase using human P450c17. Assays that were based on cytochrome c, which is not a physiologic substrate for POR, correlated poorly with clinical phenotype, but assays that were based on POR's support of catalysis by P450c17--the enzyme most closely associated with the hormonal phenotype--provided an excellent genotype/phenotype correlation. Our large survey of patients with ABS shows that individuals with an ABS-like phenotype and normal steroidogenesis have FGFR mutations, whereas those with ambiguous genitalia and disordered steroidogenesis should be recognized as having a distinct new disease: POR deficiency.

Genetics of Congenital Adrenal Hyperplasia

“…POR-inactivating mutations, including missense, frameshift and splice site mutations, are scattered throughout the gene with no apparent hot spots. 92,93 The most frequent mutation in Caucasians is p.A287P, 92 while p.R457H is the most frequent mutation in Japanese populations. 94,95 In one study of 30 patients with POR deficiency from 11 countries, 23 POR mutations including a deletion and a partial duplication were detected by MLPA, and only 22% of unrelated patients carried homozygous POR mutations.…”

A case of Antley-Bixler syndrome caused by compound heterozygous mutations of the cytochrome P450 oxidoreductase gene

“…A single basepair insertion between c.1329 and c.1330 leads to a frameshift, resulting in premature termination of translation (I444fsX449). R457H is the most frequent mutation among Japanese ABS patients [7], and causes reductions in NADPH oxidation, 17α-hydroxylase, and 17,20-lyase activities to less than 3% those recorded in normal individuals [10].…”

Preimplantation genetic diagnosis of P450 oxidoreductase deficiency and Huntington Disease using three different molecular approaches simultaneously

“…Moreover, the man carries the mutation c.1551-1552ins20 representing a 20 base pair insertion in exon 12 of the POR gene. This causes reading frame disruption that grossly disrupts the flavin mononucleotide and NADPH-binding sites of P450 oxidoreductase, inducing premature stop codon upstream of residue 616 [11].…”

“…This disorder often results in infant death. Genetically, POR deficiency is caused by mutations in the POR gene (7q11.2) and a panel of different mutations has been previously described [11].…”