Genetic variations and haplotypes of UGT1A4 in a Japanese population

Nineteen genetic variations, including 11 novel ones, were found in exon 1 and its flanking region of the UDP-glucuronosyltransferase (UGT) 1A4 gene from 256 Japanese subjects, consisting of 60 healthy volunteers, 88 cancer patients and 108 arrhythmic patients. These variations include -217T>G and -36G>A in the 5'-flanking region, 30G>A (P10P), 127delA (43fsX22; frame-shift from codon 43 resulting in the termination at the 22nd codon, codon 65), 175delG (59fsX6), 271C>T (R91C), 325A>G (R109G), and 357T>C (N119N) in exon 1, and IVS1+1G>T, IVS1+98A>G and IVS1+101G>T in the following intron. Among them, 127delA and 175delG can confer early termination of translation, resulting in an immature protein that probably lacks enzymatic activity. Variation IVS1+1G>T is located at a splice donor site and thus may lead to aberrant splicing. Since we did not find any significant differences in the frequencies of all the variations among the three subject groups, the data were analyzed as one group. The allele frequencies of the novel variations were 0.006 for IVS1+101G>T, 0.004 for 30G>A (P10P) and 357T>C (N119N), and 0.002 for the 8 other variations. In addition, the two known nonsynonymous single nucleotide polymorphisms (SNPs), 31C>T (R11W) and 142T>G (L48V), were found at 0.012 and 0.129 frequencies, respectively. The SNP 70C>A (P24T), mostly linked with 142T>G (L48V) in German Caucasians, was not detected in this study. Sixteen haplotypes were identified or inferred, and some haplotypes were confirmed by cloning and sequencing. It was shown that most of 142T>G (L48V) was linked with -219C>T, -163G>A, 448T>C (L150L), 804G>A (P268P), and IVS1+43C>T, comprising haplotype *3a; haplotype *4a harbors 31C>T (R11W); 127delA (43fsX22) and 142T>G (L48V) were linked (haplotype *5a); 175delG (59fsX6) was linked with 325A>G (R109G) (*6a haplotype); and -219C>T, -163G>A, 142T>G (L48V), 271C>T (R91C), 448T>C (L150L), 804G>A (P268P), and IVS1+43C>T comprised haplotype *7a. Our results provide fundamental and useful information for genotyping UGT1A4 in the Japanese and probably Asian populations.     

Genetic polymorphisms in CYP1A1, CYP2D6, UGT1A6, UGT1A7, and SULT1A1 genes and correlation with benzene exposure in a Chinese occupational population

Metabolic enzymes involved in benzene activation or detoxification, including cytochrome P-450 1A1 (CYP1A1), cytochrome P-450 2D6 (CYP2D6), UDP-glucuronosyltransferase 1A6 (UGT1A6), UDP-glucuronosyltransferase1A7 (UGT1A7), and sulfotransferase 1A1 (SULT1A1), were studied for their roles in human susceptibility to benzene poisoning. All 304 subjects were investigated with a unitary questionnaire and their DNA was isolated from blood samples by a routine phenol-chloroform extraction. The study included 152 benzene poisoning patients, and 152 control workers occupationally exposed to benzene in South China. The genotypes were determined by polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP) technique with genomic DNA. No individuals had the CYP 2D6 c.212 G>A variant alleles in this study. There is no association between the UGT1A6 c.181 T>A, UGT1A7 c.208 Trp>Arg, and SULT1A1 c.638 G>A genotypes and increased risk of benzene-induced carcinogenesis. Although most of the CYP2D6 haplotypes did not show any significant difference, the CYP2D6 haplotype CYP2D6 c.188 C/C, C/T, and c.4268 C/C was significantly overrepresented in the case group (OR 4.02, 95% CI: 2.53-6.39) compared with in controls. Overall, our data suggested that individuals with CYP1A1 c.5639 T/T, CYP2D6 c.188 C/C, C/T, and CYP2D6 c.4268 C/C genotypes tend to be more susceptible to benzene toxicity.     

Single nucleotide polymorphisms and haplotype frequencies of UGT2B4 and UGT2B7 in a Japanese population.

Both UDP-glucuronosyltransferase 2B4 (UGT2B4) and UGT2B7 are expressed mainly in the human liver and have several overlapping substrates; e.g., catechol estrogens, bile acids, codeine, and carvedilol. To identify novel single nucleotide polymorphisms (SNPs) and haplotypes in a Japanese population, the enhancer/promoter regions, all the exons, and the surrounding intronic regions of UGT2B4 and UGT2B7 were sequenced from 136 Japanese individuals. We found 16 and 21 polymorphisms, including 10 and 4 novel ones in UGT2B4 and UGT2B7, respectively. The novel nonsynonymous SNPs were 1364A>G (K455R) and 1531T>C (C511R) in UGT2B4 and 1192G> A (D398N) in UGT2B7. From linkage disequilibrium analysis, several SNPs in UGT2B7 were found to be highly linked with each other. No close linkage between the SNPs in UGT2B4 and UGT2B7 was observed, indicating that each gene is located within an independent haplotype block. Thus, haplotype analysis was separately performed for the two genes. In UGT2B4, we unambiguously determined 8 haplotypes and inferred an additional 12 haplotypes using an expectation-maximization-based program. In UGT2B7, five haplotypes were unambiguously assigned and an additional eight haplotypes were inferred. The haplotype structure of UGT2B7 was more diverse than that of UGT2B4 in terms of the number of frequent SNPs. In addition, ethnic differences in the UGT2B4(*)2 and UGT2B7(*)2 haplotypes between the Japanese and the Caucasian and/or African populations were found. Our findings provide fundamental and useful information for genotyping UGT2B4 and UGT2B7 in the Japanese, and probably other populations.     

Influence of UGT1A7 and UGT1A9 intronic I399 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

UGT1A7 and UGT1A9 are uridine diphosphate-glucuronosyltransferase isoforms involved in the glucuronidation of mycophenolic acid (MPA). The aim of this study was to elucidate MPA pharmacokinetics in UGT1A7 and UGT1A9 intronic I399 genotypes in Japanese adult renal transplant recipients. Eighty recipients were given repeated doses of combination immunosuppressive therapy consisting of mycophenolate mofetil and tacrolimus every 12 hours at a designated time (9:00 am and 9:00 pm). On day 28 after renal transplantation, plasma MPA concentrations were measured by high-performance liquid chromatography. All patients had UGT1A9 98TT/-275TT/-2152CC and UGT1A10 177GG/605CC genotypes. The UGT1A7*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 genotypes were detected in 35 (43.8%), five (6.2%), 28 (35.0%), eight (10.0%), and four (5.0%) patients, respectively, and the UGT1A9 I399C/C, C/T, and T/T genotypes were detected in 12 (15.0%), 33 (41.2%), and 35 (43.8%) patients of the 80 Japanese recipients. There were no significant differences in MPA pharmacokinetics among UGT1A7 or UGT1A9 intronic I399 genotype groups. The mean dose-adjusted area under the plasma concentration-time curve from zero to 12 hours (AUC0-12) of MPA in UGT1A7*1/*1, *1/*2, *1/*3, *2/*3, and *3/*3 were 95, 98, 99, 88, and 86 ng.h/mL/mg, respectively (P = 0.9475). The mean dose-adjusted AUC0-12 of MPA in UGT1A9 I399C/C, C/T, and T/T were 87, 99, and 95 ng.h/mL/mg, respectively (P = 0.6937). The dose-adjusted trough levels of MPA in UGT1A9 I399C/C, C/T, and T/T were 5.4, 5.5, and 4.7 ng/mL/mg (P = 0.5845). Although UGT1A7*3 and UGT1A9 I399C/C are known to have low-activity variants when studied in vitro, they do not have reduced in vivo MPA glucuronidation activity. UGT1A7 and UGT1A9 I399 polymorphisms do not contribute to interindividual differences in MPA pharmacokinetics.     

Genetic polymorphisms of CYP2C8 in Japanese population.

CYP2C8 plays important roles in metabolizing therapeutic drugs and endogenous compounds. Although genetic polymorphisms of CYP2C8 were reported, there is little information on CYP2C8 polymorphisms in the Japanese population. In the present study, we screened for previously described polymorphisms in the coding region of this gene using polymerase chain reaction (PCR)-restriction fragment length polymorphism or allele specific-PCR analyses. Eleven polymorphisms of CYP2C8*2 (I269F), CYP2C8*3 (R139K, K399R), CYP2C8*4 (I264M), CYP2C8*5 (frameshift), T130N, E154D, N193K, K249R, L390S, P404A, and H411L have been comprehensively investigated in at least 200 Japanese individuals. A single subject was heterozygous for CYP2C8*5, and the allele frequency was calculated as 0.0025. The other single nucleotide polymorphisms (SNPs) were not found in the Japanese subjects in the present study. Thus, it appears that the frequencies of these alleles in Japanese are extremely low. In addition, concerning the SNPs of T130N, E154D, N193K, K249R, and H411L, it remains clear that these alleles exist as polymorphisms or represent sequence errors or cloning artifacts. Although several SNPs such as CYP2C8*2, CYP2C8*3, CYP2C8*4, and P404A have been reported to reduce the enzymatic activity, pharmacokinetic abnormalities of drugs metabolized by polymorphic CYP2C8 might be rare in Japanese.     

Influence of UGT1A8 and UGT2B7 genetic polymorphisms on mycophenolic acid pharmacokinetics in Japanese renal transplant recipients

Objective UGT1A8 and UGT2B7 are important uridine diphosphate-glucuronosyltransferase isoforms for the glucuronidation of mycophenolic acid (MPA). The aim of this investigation was to elucidate MPA pharmacokinetics in UGT1A8 and UGT2B7 genotypes in Japanese renal transplant recipients. Methods Seventy-two recipients received repeated doses of mycophenolate mofetil and tacrolimus. On day 28 after renal transplantation, plasma MPA concentrations were measured for the next 24 h using high-performance liquid chromatography. UGT1A8*2 (A¹⁷³G) and UGT2B7*2 (Y²⁶⁸) were detected using a PCR-RFLP-based procedure. Results There were no significant differences in daytime and nighttime pharmacokinetics of MPA between UGT1A8 or UGT2B7 genotypes. The mean daytime dose-adjusted AUC_0–12 of MPA in UGT1A8*1/*1, *1/*2 and *2/*2 were 2.47, 2.33 and 2.57 ng·h/ml/mg/kg (P = 0.7711), and the mean nighttime AUC_0–12 were 2.15, 2.00 and 2.08 ng·h/ml/mg/kg (P = 0.4656). The mean daytime and nighttime dose-adjusted AUC_0–12 of MPA in UGT2B7*1/*1, *1/*2 and *2/*2 were 2.61, 2.24 and 2.03 ng·h/ml/mg/kg and 2.18, 1.94, and 1.45 ng·h/ml/mg/kg, respectively (P = 0.3475 and 0.2575). The mean nighttime C_max, t_max, and AUC_6–12/AUC_0–12 ratio (enterohepatic circulation and recirculation ratio) of MPA in all UGT1A8 and UGT2B7 genotypes were lower, longer, and higher, respectively, than the daytime values. Conclusions Both UGT1A8 and UGT2B7 allelic variants seem not to affect Japanese interindividual variability for plasma MPA concentration. Regardless of UGT1A8 and UGT2B7 genetic polymorphisms, the absorption of MPA through enterohepatic recirculation is higher at night.     

Genetic polymorphisms of FCGRT encoding FcRn in a Japanese population and their functional analysis

Neonatal Fc receptor (FcRn) plays an important role in regulating IgG homeostasis in the body. Changes in FcRn expression levels or activity caused by genetic polymorphisms of FCGRT, which encodes FcRn, may lead to interindividual differences in pharmacokinetics of therapeutic antibodies. In this study, we sequenced the 5'-flanking region, all exons and their flanking regions of FCGRT from 126 Japanese subjects. Thirty-three genetic variations, including 17 novel ones, were found. Of these, two novel non-synonymous variations, 629G>A (R210Q) and 889T>A (S297T), were found as heterozygous variations. We next assessed the functional significance of the two novel non-synonymous variations by expressing wild-type and variant proteins in HeLa cells. Both variant proteins showed similar intracellular localization as well as antibody recycling efficiencies. These results suggested that at least no common functional polymorphic site with amino acid change was present in the FCGRT of our Japanese population.     

Genetic polymorphisms and activity of PON1 in a Mexican population

Human paraoxonase (PON1) plays a role in detoxification of organophosphorus (OP) compounds by hydrolyzing the bioactive oxons, and in reducing oxidative low-density lipoproteins, which may protect against atherosclerosis. Some PON1 polymorphisms have been found to be responsible for variations in catalytic activity and expression and have been associated with susceptibility to OP poisoning and vascular diseases. Both situations are of public health relevance in Mexico. Therefore, the aim of this study was to evaluate PON1 phenotype and the frequencies of polymorphisms PON1 -162, -108, 55, and 192 in a Mexican population. The studied population consisted of unrelated individuals (n = 214) of either gender, 18-52 years old. Serum PON1 activity was assayed using phenylacetate and paraoxon as substrates. PON1 variants, -162, 55, and 192, were determined by real-time PCR using the TaqMan System, and PON1 -108 genotype by PCR-RFLP. We found a wide interindividual variability of PON1 activity with a unimodal distribution; the range of enzymatic activity toward phenylacetate was 84.72 to 422.0 U/mL, and 88.37 to 1645.6 U/L toward paraoxon. All four PON1 polymorphisms showed strong linkage disequilibrium (D% >90). PON1 polymorphisms -108, 55, and 192 were independently associated with arylesterase activity; whereas the activity toward paraoxon was related only with PON1 192 polymorphism, suggesting that this polymorphism is determinant to infer PON1 activity. A better understanding of the phenotype and genotypes of PON1 in Mexican populations will facilitate further epidemiological studies involving PON1 variability in OP poisoning and in the development of atherosclerosis.     

UDP-glucuronosyltransferase 1A4 polymorphisms in a Japanese population and kinetics of clozapine glucuronidation.

The UDP-glucuronosyltransferase (UGT) family plays a major role in the excretion of endobiotics and xenobiotics and their metabolites. Human UGT1A4 catalyzes the glucuronidation of primary, secondary, and tertiary amines, sapogenins, androgens, and progestins. We directly sequenced polymerase chain reaction-amplified fragments of the UGT1A4 gene from 100 healthy adult Japanese volunteers and calculated their mutation frequency. We identified four single nucleotide polymorphisms (SNPs): three in exon 1 (142T > G: L48V, 448T > C: L150L, 804G > A: P268P), and one in intron 1 (867 + 43C > T). We found three types of alleles with distinct SNP combinations that coded for different amino acid sequences: L48V-L150L-P268P-867 + 43C > T (frequency, 0.155), L48V (0.01), and P268P (0.01) (wild-type frequency was 0.825). The L48V mutant gave twice the efficiency (V(max)/K(m)) for the antipsychotic drug clozapine as the wild-type. Efficiencies of L48V for trans-androsterone, imipramine, and cyproheptadine were increased, but the efficiency for tigogenin was reduced. L48V therefore increased or decreased the glucuronidation activity, depending upon the substrates. This study shows the importance of identifying patients with the L48V polymorphism when calculating dosage, and when considering the potential adverse effects of drugs that are substrates of UGT1A4.     

Three novel single nucleotide polymorphisms in UGT1A9

Three novel single nucleotide polymorphisms (SNPs) were found in the UDP-glucuronosyltransferase (UGT) 1A9 gene from 97 Japanese subjects (47 cancer patients and 50 cardiovascular disease patients). The detected SNPs were as follows: 1) SNP, MPJ6_U1A006; GENE NAME, UGT1A9; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-AATTCTCTTAGGG/TTTCTCAGATGCC-3'. 2) SNP, MPJ6_U1A007; GENE NAME, UGT1A9; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-TGTTACGGAGTAT/GGATCTCTACAGC-3'. 3) SNP, MPJ6_U1A031; GENE NAME, UGT1A9; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-ACTCATTCTCAGG/AGGGCATGAGGTG-3'. All three SNPs were located in exon 1 with frequencies of 0.036 for MPJ6_U1A006, and 0.005 for MPJ6_U1A007 and MPJ6_U1A031. SNP MPJ6_U1A007 (726T>G) results in formation of a termination codon TAG (Y242X). The other two SNPs, MPJ6_U1A006 (588G>T) and MPJ6_U1A031 (153G>A), result in synonymous changes (G196G and R51R, respectively).     

Three novel single nucleotide polymorphisms in UGT1A10

Three novel single nucleotide polymorphisms (SNPs) were found in the UDP-glucuronosyltransferase (UGT) 1A10 gene from 24 Japanese patients with various cancers who were administered the anti-tumor drug, irinotecan (CPT-11). The detected SNPs were as follows: 1) SNP, MPJ6_U1A003; GENE NAME, UGT1A10; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-CAGATGCCATGAC/TTTTCAAGGAGAG-3'. 2) SNP, MPJ6_U1A004; GENE NAME, UGT1A10; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-CCTAGAAATAGCC/TTCTGAAATTCTC-3'. 3) SNP, MPJ6_U1A030; GENE NAME, UGT1A10; ACCESSION NUMBER, AF297093; LENGTH, 25 bases; 5'-GGTTGTAGTCATG/ACCAGAGGTGAGT-3' All the three SNPs were located in exon 1 and their frequencies were all 0.021. Among these SNPs, MPJ6_U1A003 and U1A030 resulted in amino acid alterations, T202I and M59I, respectively. The third SNP, MPJ6_U1A004, introduced a synonymous amino acid change (A231A).     

UDP-glucuronosyltransferase (UGT1A1*28 and UGT1A6*2) polymorphisms in Caucasians and Asians: relationships to serum bilirubin concentrations.

Polymorphisms that alter UDP-glucuronosyltransferase (UGT) activities have been identified. Mutations in the promoter of the UGT1A1 gene (UGT1A1*28), resulting in 5, 7 or 8, instead of 6 thymine-adenine (TA) repeats, alter bilirubin conjugation. Two missense mutations on one allele of UGT1A6 (UGT1A6*2) result in T181A and R184S amino acid substitutions and reduced activity against phenolics, such as 4-nitrophenol, 4-hydroxycoumarin and butylated hydroxy anisole. We determined the frequency of these polymorphisms in 245 healthy men and women, aged 20-40 years and examined the relationship between TA repeat number and serum bilirubin concentrations in a subset of 24 Asians and 169 Caucasians. The frequencies of the UGT1A1*28 genotypes were 0.537, 0.348, 0.098, 0.008 and 0.008 for promoter TA repeats 6/6, 6/7, 7/7, 5/6 and 6/8, respectively. Both allele and genotype frequencies varied by race (P < 0.02), with 11% of the Caucasians and none of the Asians having the 7/7 genotype. Within both ethnic groups, serum bilirubin increased with increased numbers of UGT1A1 promoter TA repeats (P = 0.0001). However, a strong ethnic group-by-UGT1A1 genotype interaction suggests that additional ethnic differences in bilirubin metabolism contribute to observed bilirubin concentrations. Genotype frequencies for UGT1A6*2 were 0.478, 0.392, 0.029, 0.090, 0.012 for wild-type (wt)/wt, wt/T181A + R184S, wt/R184S, T181A + R184S/T181A + R184S and T181A + R184S/R184S, respectively. The co-occurrence of polymorphisms in UGT1A1 and UGT1A6 differed from that expected (P < 0.0001): individuals homozygous wild-type for UGT1A1 and UGT1A6 were observed at twice the expected frequency; individuals homozygous variant for both genes were ten-fold more frequent and individuals homozygous wild-type for one gene and homozygous variant for the other were ten-fold less frequent than expected. Overall, 8% were homozygous variant for both UGT1 polymorphisms and 43% had at least one variant allele for both UGT1A1*28 and UGT1A6*2. These highly prevalent polymorphisms, which result in modified expression and activity of UGTs, may influence susceptibility to cancers associated with altered metabolism of endogenous and xenobiotic compounds.     

Irinotecan pharmacogenetics in Japanese cancer patients: roles of UGT1A1*6 and *28

Recent progress in pharmacogenetic research has made "personalized medicine" a reality, where a suitable drug at the appropriate dosage is prescribed based on individual genetic factors. Irinotecan, an anticancer drug, is one of the models for personalized medicine, and a number of clinical studies have revealed significant associations between UGT1A1(*)28 and irinotecan toxicity. Based on the cumulative evidence, clinical tests for the UGT1A1(*)28 marker have started in the United States since 2005. However, the appropriate criteria for irinotecan dose adjustments have not yet been fully established. Since there are considerable differences in genetic polymorphisms among different ethnic groups and in approved irinotecan-containing regimens between countries, the criteria for the choice of suitable genetic markers and dose adjustments should be standardized in each country. This mini-review outlines our recent studies on irinotecan pharmacogenetics and discusses the clinical significance of UGT1A1(*)6 and (*)28 markers for personalized irinotecan therapy in Japanese cancer patients.     

Interactions between human UGT1A1, UGT1A4, and UGT1A6 affect their enzymatic activities.

Protein-protein interactions between human UDP-glucuronosyltransferase (UGT) 1A1, UGT1A4, and UGT1A6 were investigated using double expression systems in HEK293 cells (UGT1A1/UGT1A4, UGT1A1/UGT1A6, and UGT1A4/UGT1A6). The substrates specific for UGT1A1 (estradiol and bilirubin), UGT1A4 (imipramine and trifluoperazine), and UGT1A6 (serotonin and diclofenac) were used to determine the effects of the coexpression of the other UGT1A isoforms on the enzymatic activity. The coexpression of UGT1A4 and UGT1A6 decreased the S(50) and V(max) values of UGT1A1-catalyzed estradiol 3-O-glucuronide formation and increased the V(max) value of UGT1A1-catalyzed bilirubin O-glucuronide formation. The coexpression of UGT1A1 decreased the V(max) value of UGT1A4-catalyzed imipramine N-glucuronide formation but had no effect on UGT1A4-catalyzed trifluoperazine N-glucuronide formation. The coexpression of UGT1A6 had no effect on UGT1A4-catalyzed imipramine N-glucuronide formation but increased the K(m) and V(max) of UGT1A4-catalyzed trifluoperazine N-glucuronide formation. The coexpression of both UGT1A1 and UGT1A4 increased the V(max) values of UGT1A6-catalyzed serotonin and diclofenac O-glucuronide formation. Thus, the effects of the coexpression of other UGT1A isoforms on the kinetics of specific activities were different depending on the UGT1A isoforms and substrates. Native polyacrylamide gel electrophoresis analysis of the double expression systems showed multiple bands at approximately 110 kDa, indicating the existence of heterodimers as well as homodimers of UGTs. In conclusion, we found that human UGT1A1, UGT1A4, and UGT1A6 interact with each other, possibly by heterodimerization, and that their effects on the enzymatic activities are complex depending on the isoforms and substrates.     

UDP-葡萄糖醛酸转移酶1A1基因多态性及其与伊立替康化疗不良反应的关系

目的 研究中国进展期胃肠道肿瘤患者UDP-葡萄糖醛酸转移酶1A1（UGT1A1）的基因多态性及其与伊立替康化疗不良反应的发生率和严重程度的关系.方法 利用聚合酶链反应-连接酶检测反应（PCR-LDR）等方法对202例进展期胃肠道肿瘤患者进行UGT1A1基因多态性检测.所有患者均采用含伊立替康方案化疗,观察并记录化疗中出现的不良反应情况,比较不同基因型患者使用伊立替康后不良反应发生率的差异.结果 202例患者中UGT1A1野生型TA6/TA6 156例（77.2％）;杂合突变型TA6/TA744例（21.8％）,纯合突变型TA7/TA7 2例（1.0％）.3～4度不良反应的情况：腹泻27例（13.4％）、白细胞减少19例（9.4％）,TA6/TA6与TA6/TA7基因型患者出现3级以上腹泻、白细胞减少与1～2级之间差异无统计学意义（P＞0.05）.TA7/TA7基因型患者出现3级以上腹泻100％,白细胞减少50％.结论 用伊立替康化疗前行UGT1A1基因多态性检测可以筛查高危人群,预测伊立替康的严重不良反应,以指导临床用药.     

Lack of association between smoking and CYP2A6 gene polymorphisms in A Japanese population.

This study determined the genotypes of the CYP2A6 gene in 96 smokers and 141 non-smokers in a Japanese population. The frequencies of wild-type of the CYP2A6* 1 and those with a whole deletion of the CYP2A6 gene were 93 (96.9%) and 3 (3.1%) in 96 smokers, and 134 (95.0%) and 7 (5.0%) in non-smokers, respectively. In addition, neither the CYP2A6* 2 nor CYP2A6* 3 alleles were observed in the population studied. There were no significant differences in the CYP2A6 genotype frequencies between smokers and non-smokers, as well as in the number of cigarettes smoked and the nicotine amounts inhaled per day between the CYP2A6* 1 and the deletion of CYP2A6. These results suggest that either the deletion or non-deletion of the CYP2A6 gene shows no significant effect on smoking behavior for the Japanese population examined.     

Genetic polymorphism of CYP2D6 in the Japanese population

The frequencies of CYP2D6 mutations in a Japanese population were investigated. Individuals were classified into three groups: control individuals, cancer patients and Parkinsonians. Genotyping for CYP2D6*3, CYP2D6*4 and CYP2D6*18 was carried out using the polymerase chain reaction, and that for CYP2D6*5 was also carried out using XbaI restriction fragment length polymorphism. The frequencies of the CYP2D6*3, CYP2D6*4, CYP2D6*5 and CYP2D6*18 mutant alleles were 0%, 0.77%, 4.10% and 0.53% in more than 256 Japanese control individuals, respectively. Based on these data, the population frequency of the CYP2D6 poor metabolizer phenotype was estimated to be 0.29%. The distribution of the four mutated alleles was not significantly different between control individuals and cancer patients or Parkinsonians.