Frequency distribution of thiopurine S-methyltransferase alleles in a polish population

Thiopurine S-methyltransferase (TPMT) is an enzyme that catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. TPMT activity exhibits an interindividual variability mainly a result of genetic polymorphism. Patients with intermediate or deficient TPMT activity are at risk for toxicity after receiving standard doses of thiopurine drugs. It has previously been reported that 3 variant alleles:TPMT*2, *3A, and *3C are responsible for over 95% cases of lower enzyme activity. The purpose of this study was to determine the frequency of TPMT variant alleles in a Polish population. DNA samples were obtained from 358 unrelated healthy Polish subjects of white origin, and TPMT genetic polymorphism was determined using PCR-RFLP and allele-specific PCR methods. The results showed that allelic frequencies were 0.4% for TPMT*2, 2.7% for TPMT*3A, and 0.1% for TPMT*3C, respectively. A TPMT*3B allele was not found in the studied population. The general pattern of TPMT allele disposition in the Polish population is similar to those determined for other white populations, but the frequency of total variant alleles is lower than in other European populations studied to date.     

Genotype and allele frequencies of TPMT,NAT2, GST,SULT1A1 and MDR-1 in the Egyptian population

AIMS: The goal of this study was to determine the frequencies of important allelic variants in the TPMT, NAT2, GST, SULT1A1 and MDR-1 genes in the Egyptian population and compare them with the frequencies in other ethnic populations. METHODS: Genotyping was carried out in a total of 200 unrelated Egyptian subjects. TPMT*2 was detected using an allele-specific polymerase chain reaction (PCR) assay. TPMT*3C and NAT2 variants (*5,*6 and *7) were detected using an allele-specific real-time PCR assay. Detection of GSTM1 and GSTT1 null alleles was performed simultaneously using a multiplex PCR assay. Finally, a PCR-restriction fragment length polymorphism assay was applied for the determination of TPMT*3A (*3B), SULT1A1*2 and MDR-1 (3435T) variants. RESULTS: Genotyping of TPMT revealed frequencies of 0.003 and 0.013 for TPMT*3A and TPMT*3C, respectively. No TPMT*2 or *3B was detected in the analysed samples. The frequencies of specific NAT2 alleles were 0.215, 0.497, 0.260 and 0.028 for *4 (wild-type), *5 (341C), *6 (590A) and *7 (857A), respectively. GSTM1 and GSTT1 null alleles were detected in 55.5% and 29.5% of the subjects, respectively. SULT1A1*2 was detected at a frequency of 0.135. Finally, the frequencies of the wild-type allele (3435C) and the 3435T variant in the MDR-1 gene were found to be 0.6 and 0.4, respectively. CONCLUSIONS: We found that Egyptians resemble other Caucasians with regard to allelic frequencies of the tested variants of NAT2, GST and MDR-1. By contrast, this Egyptian population more closely resemble Africans with respect to the TPMT*3C allele, and shows a distinctly different frequency with regard to the SULT1A1*2 variant. The predominance of the slow acetylator genotype in the present study (60.50%) could not confirm a previously reported higher frequency of the slow acetylator phenotype in Egyptians (92.00%), indicating the possibility of the presence of other mutations not detectable as T341C, G590A and G857A. The purpose of our future studies is to investigate for new polymorphisms, which could be relatively unique to the Egyptian population.     

Frequencies of thiopurine S-methyltransferase mutant alleles (TPMT*2, *3A, *3B and *3C) in 151 healthy Japanese subjects and the inheritance of TPMT*3C in the family of a propositus

AIMS: To determine the frequencies of four thiopurine S-methyltransferase (TPMT) mutant alleles, TPMT*2, *3A, *3B and *3C in a normal Japanese population. METHODS: Genotypes were determined in 151 Japanese subjects and in six family members of a propositus using polymerase chain reaction (PCR)-restriction fragment length polymorphism and allele-specific PCR assays. RESULTS: Only one TPMT*3C heterozygote was identified (gene frequency 0.3%). TPMT*2, *3A and *3B were not detected. In addition, TPMT*3C was found to have been inherited from the mother and passed on to the son of the propositus. CONCLUSIONS: TPMT*3C appears to be most prevalent among the known mutant allele of TPMT in a Japanese population which may have some relevance for the treatment of Japanese patients with thiopurine drugs.     

Genotyping of thiopurine methyltransferase using pyrosequencing

Thiopurine methyltransferase (TPMT) metabolizes thiopurine drugs which are used in the treatment of leukemia and some autoimmune diseases. Previously, 11 mutant alleles of TPMT gene (TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8) have been reported. These mutant alleles may cause life-threatening toxicity in patients exposed to thiopurine drugs, 6-mercaptopurine and azathioprine. We have developed a rapid and accurate protocol for TPMT genotype determination using Pyrosequencing(TM) technology in 96 Japanese subjects. Five fragments of the TPMT gene (exon 4, 5, 7, 8, 10) were amplified by PCR, and the 10 single-nucleotide polymorphisms (SNPs) for TPMT*1S, *2, *3A, *3B, *3C, *3D, *4, *5, *6, *7, and *8 were sequenced. The results of this pyrosequencing method corresponded exactly with those of the DNA sequencing method using BigDye terminator chemistry. We have demonstrated that typing of 10 SNPs can be performed within 30 min. Pyrosequencing has a wide application in the large-scale identification of individual TPMT genotypes.     

The frequency and distribution of thiopurine methyltransferase alleles in Caucasian and Asian populations

Thiopurine methyltransferase metabolizes 6-mercaptopurine, thioguanine and azathioprine, thereby regulating cytotoxicity and clinical response to these thiopurine drugs. In healthy Caucasian populations, 89-94% of individuals have high thiopurine methyltransferase activity, 6-11% intermediate and 0.3% low, resulting from genetic polymorphism. Four variant thiopurine methyltransferase alleles were detected in over 80% of individuals with low or intermediate thiopurine methyltransferase activity. The wild-type allele is defined as TPMT*1 and the mutant alleles are TPMT*2 (G238C), TPMT*3A (G460A and A719G), TPMT*3B (G460A) and TPMT*3B (A719G). The frequency of these alleles in different ethnic groups is not well defined. In this study, DNA from 199 British Caucasian, 99 British South West Asian and 192 Chinese individuals was analysed for the presence of these variant alleles using polymerase chain reaction-restriction fragment length polymorphism and allele-specific polymerase chain reaction based assays. The frequency of individuals with a variant thiopurine methyltransferase genotype was: Caucasians 10.1% (20/199), South West Asians 2.0% (2/99) and Chinese 4.7% (9/192). Two TPMT*2 heterozygotes were identified in the Caucasian population, but this allele was not found in the two Asian populations. TPMT*3A was the only mutant allele found in the South West Asians (two heterozygotes). This was also the most common mutant allele in the Caucasians (16 heterozygotes and one homozygote) but was not found in the Chinese. All mutant alleles identified in the Chinese population were TPMT*3C (nine heterozygotes). This allele was found at a low frequency in the Caucasians (one heterozygote). This suggests that A719G is the oldest mutation, with G460A being acquired later to form the TPMT*3A allele in the Caucasian and South West Asian populations. TPMT*2 appears to be a more recent allele, which has only been detected in Caucasians to date. These ethnic differences may be important in the clinical use of thiopurine drugs.     

Functional characterization of 23 allelic variants of thiopurine S-methyltransferase gene (TPMT*2 - *24)

OBJECTIVE: Thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of the widely used thiopurine drugs. TPMT is genetically polymorphic and is associated with large interindividual variations in thiopurine drug toxicity and therapeutic efficacy. In this study, we performed an in-vitro analysis of TPMT variant alleles, namely, TPMT*2, *3A, *3B, *3C, *5, *6, *7, *8, *9, *10, *11, *12, *13, *14, *16, *17, *18, *19, *20, *21, *22, *23, and *24. METHODS: The wild-type TPMT proteins, TPMT.1 and 23 variants were heterologously expressed in COS-7 cells, and the kinetic parameters Km, Vmax, and intrinsic clearance (Vmax/Km) of 6-thioguanine S-methylation were determined. RESULTS: The expression levels of TPMT.2, TPMT.3A, TPMT.5, TPMT.12, TPMT.14, and TPMT.22 were considerably lower than that of TPMT.1 (P<0.005), and that of TPMT.18 was slightly reduced (P<0.05). The kinetic parameters of TPMT.3A, TPMT.3B, TPMT.5, TPMT.14, TPMT.18, TPMT.21, and TPMT.22 could not be accurately established because of no activity in 6-thioguanine S-methylation. The Vmax/Km values of TPMT.2, TPMT.7, TPMT.17, and TPMT.24 were displayed less than 10% of the wild-type. CONCLUSION: This functional analysis with respect to TPMT variants could provide useful information for individualization of thiopurine drugs therapy.     

河南地区汉族人群药物代谢酶CYP2C19，NAT2和TPMT基因多态性分析(英文)

目的：了解细胞色素P450(cytochromes P450,CYP)2C19,N-乙酰基转移酶2(arylamine N- acetyltransferase 2,NAT2)和硫嘌呤甲基转移酶(thiopurine S-methyltransferase,TPMT)基因常见的遗传多态性在河南地区汉族人群中的分布及其频率。方法：应用聚合酶链反应-限制性片段长度多态性分析(PCR-RFLP)对210名河南地区汉族人群的CYP2C19突变基因(*2和*3)、NAT2突变基因(*6和*7)和TPMT突变基因(*3A,*3B和*3C)进行检测。用聚合酶链反应-等位基因特异性扩增(PCR-ASA)对NAT2突变基因(*5)和TPMT突变基因(*2)进行检测。结果：CYP2C19*2和*3等位基因分布频率分别为34．76%和6．4%,同时携带2个等位突变基因的慢基因型频率占14．8%。NAT2*4(wt),*5(341C),*6(590A)和*7(857A)等位基因分布频率分别为59．1%,4．1%,26．4%和9．5%,慢基因型分布频率占19．5%。TPMT*3C等位基因分布频率为1．2%,未发现TPMT*2,TPMT*3A或TPMT*3B。结论：CYP2C19,NAT2和TPMT基因常见的遗传多态性在汉族人群中的分布及其频率与白人存在明显差异,这将有助于我国汉族人群临床药动学研究和给药剂量的确定。     

Genotype–phenotype correlation for thiopurine S-methyltransferase in healthy Italian subjects

OBJECTIVE: The aim of the present study was to estimate the concordance rate between erythrocyte thiopurine methyltransferase (TPMT) activity and genotype at the TPMT locus in an Italian population sample. METHODS: The TPMT phenotype and genotype were determined in an unrelated population of 103 Italian healthy blood donors. Erythrocyte TPMT activity was measured with a radiochemical assay using 12.5 microM S-adenosyl-L-(methyl-14C)-methionine and 4 mM 6-mercaptopurine. The genotyping assay was based on restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) and allele-specific oligonucleotide polymerase chain reaction (ASO-PCR) methods. RESULTS: All subjects had detectable TPMT activity. The activity of TPMT varied 2.8-fold between the 5th and 95th percentile. This variation was neither age (P = 0.63) nor gender (P = 0.44) regulated and the frequency distribution of TPMT activity is compatible with a polymorphic distribution. The presence of the four most common defective alleles, i.e. TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C, was examined through the entire phenotyped population. Ninety-two subjects did not carry any of the tested mutations. Eleven individuals were heterozygous for one of the mutant alleles and had a TPMT activity lower than 30 pmol/min/mg. Eight subjects were TPMT*1/TPMT*3A, two TPMT*1/TPMT*3C and one was TPMT*1/TPMT*2. The TPMT*3B allele was not detected in the samples analysed. CONCLUSION: There was a concordance of 97% between genotype and phenotype. All the heterozygotes had an intermediate phenotype. However, the wide variation range in TPMT activity detected in the wild-type homozygotes indicates that other genetic or epigenetic factors influence the TPMT phenotype.     

Ethnic differences in thiopurine methyltransferase pharmacogenetics: evidence for allele specificity in Caucasian and Kenyan individuals

Thiopurine methyltransferase (TPMT) degrades 6-mercaptopurine, azathioprine and 6-thioguanine which are commonly used in the treatment of autoimmune diseases, leukaemia and organ transplantation. TPMT activity is polymorphic as a result of gene mutations. Heterozygous individuals have an increased risk of haematological toxicity after thiopurine medication, while homozygous mutant individuals suffer life threatening complications. Previous population studies have identified ethnic variations in both phenotype and genotype, but limited information is available within African populations. This study determined the frequency of common TPMT variant alleles in 101 Kenyan individuals and 199 Caucasians. The frequency of mutant alleles was similar between the Caucasian (10.1%) and Kenyan (10.9%) populations. However, all mutant alleles in the Kenyan population were TPMT*3C compared with 4.8% in Caucasians. In contrast TPMT*3A was the most common mutant allele in the Caucasian individuals. This study confirms ethnic differences in the predominant mutant TPMT allele and the findings will be useful for the development of polymerase chain reaction-based strategies to prevent toxicity with thiopurine medications.     

Molecular analysis of thiopurine S-methyltransferase alleles in South-east Asian populations

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. In Caucasians, four variant TPMT alleles have been detected in over 80% of individuals with low or intermediate TPMT activity. The wild-type allele is designated as TPMT*1 and the mutant alleles are designated TPMT*2 through TPMT*8. The frequency of these alleles in different ethnic groups has not been well defined. In this study, one hundred individuals, from each of the Indonesian, Thai and Philippine populations, together with 249 Taiwanese, were analysed by polymerase chain reaction-restriction fragment length polymorphism and direct sequencing methods. The results showed that the allelic frequencies of TPMT*3C were 0.6% for Taiwanese and 1% for Filipino, Thai and Indonesian populations, respectively. One Filipino with a Caucasian parent was found to be heterozygous for the TPMT*2 allele. This study provides the first analysis of the allele frequency distribution of all known TPMT mutations in South-east Asian populations.     

Frequency distribution of thiopurine S-methyltransferase activity in red blood cells of a healthy Japanese population

Thiopurine S-methyltransferase (TPMT), which exhibits a genetic polymorphism, plays an important role in the metabolism of thiopurine drugs such as mercaptopurine, thioguanine, and azathioprine. To determine the frequency distribution of TPMT activity in 157 Japanese subjects with different TPMT genotypes, ie, TPMT*1/*1 and TPMT*1/*3, the authors measured levels of 6-methylmercaptopurine formed from 6-mercaptopurine in red blood cells lysates by HPLC. The TPMT activities in our Japanese subjects ranged from 11.0 to 42.6 pmol/h/mgHb. Although the mean value of TPMT activities in 6 subjects with TPMT*1/*3C (20.3 +/- 8.1 pmol/h/mgHb) was 25% lower than that in 151 subjects with TPMT*1/*1 (27.0 +/- 5.1 pmol/h/mgHb), there was overlap. The ranges of TPMT activity in subjects with TPMT*1/*1 and those with TPMT*1/*3C were similar. The median values in TPMT*1/*3C and TPMT*1/*1 individuals were 20.1 (11.0-31.2) and 26.8 pmol/h/mgHb (15.7-42.7), respectively (Mann-Whitney U-test: median difference 6.7 pmol/h/mgHb, 95% CI 0-25.5, P < 0.05). This observation may have relevance for the use of 6-mercaptopurine and azathioprine as therapeutic agents in Japanese patients.     

Characterisation of novel defective thiopurine S-methyltransferase allelic variants

Human thiopurine S-methyltransferase (TPMT, EC 2.1.1.67) is a key enzyme in the detoxification of thiopurine drugs widely used in the treatment of various diseases, such as inflammatory bowel diseases, acute lymphoblastic leukaemia and rheumatic diseases. The TPMT gene is genetically polymorphic and the inverse relationship between TPMT activity and the risk of developing severe hematopoietic toxicity is well known. In this study, the entire coding sequence of TPMT, together with its 5'-flanking promoter region, was analysed in patients with an intermediate phenotype for thiopurine drug methylation. Four polymorphisms were identified, two previously described, c.356A>C (p.Lys(119)Thr, TPMT*9) and c.205C>G (p.Leu(69)Val, TPMT*21), and two novel missense mutations, c.537G>T (p.Gln(179)His, TPMT*24) and c.634T>C (p.Cys(212)Arg, TPMT*25). Structural investigations, using molecular modeling, were undertaken in an attempt to explain the potential impact of the amino acid substitutions on the structure and activity of the variant proteins. Additionally, in order to determine kinetic parameters (K(m) and V(max)) of 6-thioguanine (6-TG) methylation, the four variants were expressed in a recombinant yeast expression system. Assays were performed by HPLC and the results were compared with those of wild-type TPMT. The p.Leu(69)Val and the p.Cys(212)Arg substitutions encode recombinant enzymes with a significantly decreased intrinsic clearance compared to that of the wild-type protein, and, consequently, characterise non-functional alleles of TPMT. The p.Lys(119)Thr and the p.Gln(179)His substitutions do not affect significantly the catalytic activity of the corresponding variant proteins, which prevents to unambiguously describe these latter alleles as defective TPMT variants.     

Phenotyping and genotyping study of thiopurine S-methyltransferase in healthy Chinese children: a comparison of Han and Yao ethnic groups

AIMS: Ethnicity is an important variable influencing drug response. Thiopurine S-methyltransferase (TPMT) plays an important role in the metabolism of thiopurine drugs. Previous population studies have identified ethnic variations in both phenotype and genotype of TPMT, but limited information is available within Chinese population that comprises at least 56 ethnic groups. The current study was conducted to compare both phenotype and genotype of TPMT in healthy Han and Yao Chinese children. METHODS: TPMT activity was measured in healthy Chinese children by a HPLC assay (n = 213, 87 Han Chinese and 126 Yao Chinese). Allele-specific polymerase chain reaction (PCR) and PCR-restriction fragment length polymorphism (RFLP) were used to determine the frequency of TPMT mutant alleles (TPMT*2, TPMT*3 A, TPMT*3B and TPMT*3C) in these children. RESULTS: There was no significant difference in the mean TPMT activity between Han and Yao Chinese children. A unimodal distribution of TPMT activity in Chinese children was found and the mean TPMT activity was 13.32 +/- 3.49 U ml(-1) RBC. TPMT activity was not found to differ with gender, but tended to increase with age in Yao Chinese children. TPMT*2, TPMT*3B and TPMT*3A were not detected, and only one TPMT*3C heterozygote (Han child) was identified in 213 Chinese children. Erythrocyte TPMT activity of this TPMT*3C heterozygote was 12.36 U ml(-1) RBC. The frequency of the known mutant TPMT alleles was 0.2%[1/426] in Chinese children. CONCLUSION: The frequency distribution of RBC TPMT activity was unimodal. The frequency of the known mutant TPMT alleles in Chinese Children is low and TPMT*3C appears to be the most prevalent among the tested mutant TPMT alleles in this population.     

Genetic determinants of the thiopurine methyltransferase intermediate activity phenotype in British Asians and Caucasians

OBJECTIVE: Polymorphisms in the TPMT gene open reading frame (ORF) are associated with reduced TPMT activity. Variable number tandem repeats (VNTR*3 to VNTR*9) in the promoter region of the gene consisting of combinations of Type A, B and C repeat units, may modulate TPMT activity. Here we present the allele frequencies of genetic modifiers of TPMT activity in a British Asian population, as well as the concordance between intermediate TPMT activity and ORF and VNTR genotypes in a predominantly Caucasian population. METHODS: VNTR type and ORF mutations were determined in two selected TPMT activity ranges, intermediate activity (4-8 U, 108 patients), normal (12-15 U, 53 patients) and in 85 British Asians. RESULTS: In British Asians, TPMT*3C was the prevalent mutant allele (four heterozygotes). One patient was heterozygous for TPMT*3A. Overall VNTR frequencies did not differ from Caucasians. Three new VNTR alleles were designated VNTR*6c, VNTR*6d, and VNTR*7c. Forty-one percent of patients with intermediate activity were heterozygous for a TPMT ORF mutation (3A, 2B, 1C). Marked linkage disequilibrium was noted between VNTR*6b - TPMT*3A (D' = 1), VNTR*4b - TPMT*3C (D' = 0.67) and VNTR*6a - TPMT*1 (D' = 1) alleles. As a result, significant differences (P < 0.05) in the distribution of Type A, B or the total number of repeats summed for both alleles, were found between the ORF heterozygous intermediate activity group and the wild-type intermediate or normal activity groups. No significant difference was found between the two wild-type groups. CONCLUSION: Our results suggest that TPMT gene VNTRs do not significantly modulate enzyme activity.     

Comprehensive analysis of thiopurine S-methyltransferase phenotype-genotype correlation in a large population of German-Caucasians and identification of novel TPMT variants

The thiopurine S-methyltransferase (TPMT) genetic polymorphism has a significant clinical impact on the toxicity of thiopurine drugs. It has been proposed that the identification of patients who are at high risk for developing toxicity on the basis of genotyping could be used to individualize drug treatment. In the present study, phenotype-genotype correlation of 1214 healthy blood donors was investigated to determine the accuracy of genotyping for correct prediction of different TPMT phenotypes. In addition, the influence of gender, age, nicotine and caffeine intake was examined. TPMT red blood cell activity was measured in all samples and genotype was determined for the TPMT alleles *2 and *3. Discordant cases between phenotype and genotype were systematically sequenced. A clearly defined trimodal frequency distribution of TPMT activity was found with 0.6% deficient, 9.9% intermediate and 89.5% normal to high methylators. The frequencies of the mutant alleles were 4.4% (*3A), 0.4% (*3C) and 0.2% (*2). All seven TPMT deficient subjects were homozygous or compound heterozygous carriers for these alleles. In 17 individuals with intermediate TPMT activity discordant to TPMT genotype, four novel variants were identified leading to amino acid changes (K119T, Q42E, R163H, G71R). Taking these new variants into consideration, the overall concordance rate between TPMT genetics and phenotypes was 98.4%. Specificity, sensitivity and the positive and negative predictive power of the genotyping test were estimated to be higher than 90%. Thus, the results of this study provide a solid basis to predict TPMT phenotype in a Northern European Caucasian population by molecular diagnostics.     

Allelotype frequency of the thiopurine methyltransferase (TPMT) gene in Japanese

Polymorphisms at three loci in the thiopurine methyltransferase (TPMT) gene are known to be responsible for azathioprine and 6-mercaptopurine (6MP) toxicity. Among them, only TPMT*3C variant allele with A719G mutation was found in 15/522 (2.9%; 17/1044 alleles; 1.6%) Japanese individuals including two homozygotes. The allele frequency was different from that in Caucasians, and investigation of TPMT polymorphisms with consideration of ethnic differences before administration of azathioprine or 6MP may provide clinically useful information.     

Phenotypic and genotypic analysis of thiopurine s-methyltransferase polymorphism in the bulgarian population

Genetic polymorphism of TPMT activity is an important factor responsible for large individual differences in thiopurine toxicity and therapeutic efficacy. The aim of this study was to determine the distribution of TPMT activity as well as the types and frequencies of mutant alleles in a Bulgarian population sample. TPMT activity was measured in 313 Bulgarians, using an established HPLC procedure. All individuals with TPMT activity less than 12.0 nmol/(mL Ery.h) (n = 76) were additionally genotyped using a color multiplex hybridization assay. The samples were tested for TPMT*2, *3A, *3B, *3C, *3D, *4, and *6 mutant alleles. TPMT activities varied from 1.1 to 24.0 nmol/(mL Ery.h) [mean 14.2 +/- 3.2 nmol/(mL Ery.h)]: 92.3% of the individuals investigated had high TPMT activity [>10 nmol/(mL Ery. h)], whereas 7.4% were intermediate [2.8-10 nmol/(mL Ery.h)], and 0.3% were low metabolizers [< 2.8 nmol/(mL Ery.h)]. A significant gender-related difference in TPMT activity (P = 0.02) was observed with 6.2% higher values in men than in women. There was no significant correlation between age and enzyme activity (r = 0.06, P = 0.27). Genotype analysis revealed three mutant TPMT alleles: 2, 3A, and 3C. The frequency of these alleles among the TPMT-deficient individuals was 2.17%, 30.4%, and 2.17%, respectively. These data show a similar distribution of TPMT activity among the Bulgarian population investigated as in most other white populations with the frequency of intermediate metabolizers being somewhat lower (7.4% versus approximately 11%) in the Bulgarians. The most common variant allele was TPMT-3A, as in other white populations.     

Thiopurine S-methyltransferase genetic polymorphism in the Thai population

AIMS: To determine the incidence of the thiopurine S-methyltransferase (TPMT) genetic polymorphism in the Thai population. METHODS: Genomic DNAs were isolated from peripheral blood leucocytes of 200 healthy Thais. The frequencies of five allelic variants of the TPMT gene, TPMT*2, *3A, *3B, *3C and *6 were determined using allele specific polymerase chain reaction (PCR) or PCR-Restriction fragment length polymorphism technique. RESULTS: Of the 200 Thai subjects participating in this study, 181 subjects (90.5%) were homozygous for TPMT*1, 18 subjects (9.0%) were heterozygous for TPMT*1/*3C. Only one subject (0.5%) was homozygous for TPMT*3C. The frequency of TPMT*3C mutant allele was 0.050. CONCLUSIONS: Although the TPMT*3C is the most prevalent mutant allele in Asian populations, the frequency of this defective allele is significantly higher in Thais than has been reported in other Asian populations.     

Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan O-demethylation in different CYP2D6 genotypes

AIMS: To determine the frequencies of 11 CYP2D6 mutant alleles (CYP2D6*2, *3, *4, *5, *8, *10, *11, *12, *14, *17 and *18), and their relation to the metabolic capacity of CYP2D6 in Japanese subjects. METHODS: One hundred and sixty-two unrelated healthy Japanese subjects were genotyped with the polymerase chain reaction amplification method and 35 subjects were phenotyped with dextromethorphan. RESULTS: The frequencies of CYP2D6*2,*5, *10 and *14 were 12.9, 6.2, 38.6 and 2.2% in our Japanese subjects, respectively. CYP2D6*3, *4, *8, *11, *12, *17 and *18 were not detected. The mean log metabolic ratio of dextromethorphan in subjects with genotypes predicting intermediate metabolizers was significantly greater than that of heterozygotes for functional and defective alleles. CONCLUSIONS: CYP2D6*5 and CYP2D6*14 are the major defective alleles found in Japanese subjects. In addition, CYP2D6*10 may play a more important role than previously thought for the treatment of Japanese patients with drugs metabolized by CYP2D6.     

Genetic polymorphism of UDP-glucuronosyltransferase 2B7 (UGT2B7) at amino acid 268: ethnic diversity of alleles and potential clinical significance

UGT2B7 catalyses the glucuronidation of a diverse range of drugs, environmental chemicals and endogenous compounds. Hence, coding region polymorphisms of UGT2B7 are potentially of pharmacological, toxicological and physiological significance. Two variant UGT2B7 cDNAs encoding enzymes with either His or Tyr at residue 268 have been isolated. The variants, referred to as UGT2B7*1 and UGT2B7*2, respectively, arise from a C to T transversion at nucleotide 802 of the UGT2B7 coding region. Analysis of genomic DNA from 91 unrelated Caucasians and 84 unrelated Japanese demonstrated the presence of the variant alleles encoding UGT2B7*1 and UGT2B7*2 in both populations. However, while there was an approximately equal distribution of subjects homozygous for each allele in the Caucasian population, subjects homozygous for the UGT2B7*1 allele were over 10-fold more prevalent than UGT2B7*2 homozygotes in Japanese. The frequencies of the UGT2B7*1 and UGT2B7*2 alleles were 0.511 and 0.489, respectively, in Caucasians, and 0.732 and 0.268, respectively, in Japanese. The 95% confidence intervals for the two alleles did not overlap between Caucasians and Japanese. Rates of microsomal androsterone, menthol and morphine (3-position) glucuronidation were determined for genotyped livers from Caucasian donors. Statistically significant inter-genotypic differences were not apparent for any of the three substrates. Although the UGT2B7 polymorphism characterized here is probably not associated with altered enzyme activity, the results highlight the need to consider ethnic variability in assessing the consequences of UGT polymorphisms.