Novel Mutations of the CYP2A6 Gene in a Thai Population with Lowered Capacity of Coumarin 7-Hydroxylation

Decreased coumarin 7-hydroxylase activities and CYP2A6 expression levels in humans caused by genetic polymorphism in CYP2A6 promoter region (CYP2A6*9)

One of seven poor metabolizers of coumarin found in Thai subjects was previously genotyped as heterozygote for the CYP2A6*4 (whole deletion) and CYP2A6*9. Thus, we aimed to investigate the relationship between the genetic polymorphism in the TATA box of the CYP2A6 gene (CYP2A6*9), expression levels of CYP2A6 mRNA and coumarin 7-hydroxylase activities in human livers. Levels of CYP2A6 mRNA were quantified by real-time quantitative reverse transcriptase-polymerase chain reaction. The mean expression levels of CYP2A6 mRNA in individuals with CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 58%, 71% and 21% of the individuals genotyped as CYP2A6*1/*1, respectively. The mean in-vitro coumarin 7-hydroxylase activities in subjects carrying CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 41%, 71% and 12%, respectively, compared to those of the subjects judged as wild-type. Vmax values for coumarin 7-hydroxylation in the liver microsomes from human subjects with genotypes of CYP2A6*1/*1, CYP2A6*1/*4, CYP2A6*1/*9 and CYP2A6*4/*9 were 0.58, 0.26, 0.44 and 0.13 nmol/min/nmol total P450, respectively. CYP2A6 protein levels in human liver microsomes with the CYP2A6*4 and the CYP2A6*9 alleles were markedly decreased. These results suggest that the genetic polymorphism in the promoter region of the CYP2A6 gene (CYP2A6*9) reduced the expression levels of CYP2A6 mRNA and protein in human livers, resulting in the decrease of coumarin 7-hydroxylase activities. Individuals judged as CYP2A6*4/*9 were expected to be poor metabolizers, having extremely low activity of CYP2A6.

Eighteen Novel Polymorphisms of the CYP2A13 Gene in Japanese

We sequenced all nine exons, exon-intron junctions including a part of introns, 5'-flanking and 3'-untranslated regions of the cytochrome P450 (CYP) 2A13 gene from 192 Japanese individuals. We found eighteen novel genetic polymorphisms including five single nucleotide polymorphisms (SNP) and one three base pair insertion causing amino acid substitution and one amino acid insertion, respectively, one silent SNP in exon 4, four SNPs in a 5'-flanking region, and seven SNPs in introns. The five SNPs (74G>A in exon 1, 579G>A in exon 2, 1706C>G in exon 3, and 7343T>A and 7465C>T in exon 9) causing amino acid substitutions (Arg(25)Gln, Arg(101)Gln, Asp(158)Glu, Phe(453)Tyr, and Arg(494)Cys), respectively. The one three base pair insertion (1634_1635 ACC insertion in exon 3) caused one amino acid insertion ((133_134)Thr ins). These sequences are as follows:SNP, 021125Fujieda005; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base;5'-TGTCAGTCTGGCG/AGCAGAGGAAGAG-3'.SNP, 021125Fujieda007; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base; 5'-AGTTCAGCGGGCG/AAGGCGAGCAGGC-3'.SNP, 021125Fujieda009; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base; 5'-CTTCCTCATCGAC/GGCCCTCCGGGGC-3'.SNP, 021125Fujieda017; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base; 5'-TCTTTCTCTTCTT/ACACCACCATCAT-3'.SNP, 021125Fujieda018; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base; 5'-AGCTTCCTGCCCC/TGCTGAGCGAGGG-3'.SNP, 021125Fujieda008; GENE NAME, CYP2A13; ACCESSION NUMBER, NG_000008; LENGTH, 25 base; 5'-CTCCATCGCCACC-/ACCCTAAGGGGTTTT-3'.

Twenty One Novel Single Nucleotide Polymorphisms (SNPs) of the CYP2A6 Gene in Japanese and Caucasians

We sequenced all nine exons and exon-intron junctions of the CYP2A6 gene from 33 Japanese and 28 Caucasians. We found twenty one single nucleotide polymorphisms (SNPs) including four SNPs causing amino acid substitutions, one silent SNP in exon 5, one SNP in a 5'-flanking region, four SNPs in a 3'-untranslated region, and eleven SNPs in introns. The four mutations (13G>A and 86G>A in exon 1, and 2134A>G and 2161C>T in exon 4) causing amino acid substitutions (Gly(5)Arg, Ser(29)Asn, Lys(194)Glu, and Arg(203)Ser), respectively, were as follows: SNP, 020719Kiyotani004; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-ATGCTGGCCTCAG/AGGATGCTTCTGG-3'. SNP, 020719Kiyotani005; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-AGCAGAGGAAGAG/ACAAGGGGAAGCT-3'. SNP, 020719Kiyotani011; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-CGCTTTGACTATA/GAGGACAAAGAGT-3'. SNP, 020719Kiyotani012; GENE NAME, CYP2A6; ACCESSION NUMBER, NG_000008.4; LENGTH, 25 base; 5'-CTGTCACTGTTGC/TGCATGATGCTAG-3'. New alleles having these SNPs were designated as CYP2A6( *)13-CYP2A6( *)16.