肾移植患者HGPRT活性及多态性与硫唑嘌呤所致不良反应的相关性研究

目的:本研究旨在探索次黄嘌呤鸟嘌呤磷酸核糖转移酶(HGPRT)活性及基因多态性与硫唑嘌呤(AZA)所致不良反应的相关性,为临床合理使用AZA提供理论依据。方法:用本实验室建立的HPLC法测定入选样本的HGPRT活性,直接测序法测定HGPRT IVS6-12C>A的基因型,结合受试者不良反应发生情况,分析HGPRT活性及多态性与AZA所致不良反应的相关性。结果:86例肾移植受者HGPRT活性范围为(44.59~262.16)U,平均为(100.17±33.50)U,健康受试者HGPRT活性范围为(28.43~153.65)U,平均为(99.30±17.21)U,均呈正态分布。两组HGPRT活性均值差异无统计学意义(P>0.05)。304例肾移植患者中发现2例HGPRT IVS6-12C>A突变体,突变频率为2.30%。而健康受试者中未发现突变,分析发现HGPRT活性与基因型之间无明显相关性(P>0.05)。流行性感冒样症状组患者的平均HGPRT活性明显高于肾移植对照组[(147.47±101.24)Uvs(100.46±29.31)U,P<0.05)],而血液毒性组、肝脏毒性组、胃肠道反应组与肾移植对照组比较,活性差异无统计学意义。AZA所致不良反应与HGPRT基因多态性之间没有明显相关性(P>0.05)。结论:在服用AZA之前,测定患者HGPRT活性,筛选出HGPRT高活性者,减少AZA的初始剂量,有利于减少AZA所致流行性感冒样症状不良反应的发生率。     

肾移植受者红细胞ITPA活性与硫唑嘌呤不良反应关系的研究

目的建立一种测定三磷酸肌苷焦磷酸酶(ITPA)活性的高效液相色谱法(HPLC),探讨ITPA活性与硫唑嘌呤(AZA)导致的不良反应的关系。方法应用新建立的高效液相色谱法测定110例肾移植患者红细胞ITPA活性,分析ITPA活性在发生了不良反应的患者与未发生不良反应的患者间的差异。结果110例患者红细胞ITPA活性范围为2.0～575.7U,平均为(373.4±148.3)U,ITPA活性在男性和女性患者间无差异(P>0.05)。将76例未发生不良反应的患者作为对照组,其平均ITPA活性为(391.1±140.5)U。10例发生了血液毒性和14例发生了肝脏毒性的患者平均ITPA活性与对照组患者比较无差异(P>0.05)。10例发生了胃肠紊乱的患者平均ITPA活性为(177.1±69.6)U,明显低于未发生不良反应的患者(P<0.05)。结论硫唑嘌呤所致的血液毒性和肝脏毒性与ITPA活性无明显相关性,硫唑嘌呤所致的胃肠紊乱与ITPA活性低下有关。ITPA活性测定对指导临床硫唑嘌呤的合理应用具有一定意义。     

硫嘌呤类药物遗传药理学研究进展

临床上硫嘌呤类药物应用广泛,但在此类药物的使用过程中,血液毒性、肝脏毒性、胰腺炎等不良反应的发生率较高。研究发现,硫嘌呤甲基转移酶(thiopurine S-methyltransferase,TPMT)的活性和遗传多态性,以及三磷酸肌苷焦磷酸酶(inosine triphosphate pyrophosphatase,ITPA)的遗传多态性与硫嘌呤类药物不良反应的发生密切相关。本文综述了TPMT活性和基因多态性,以及ITPA基因多态性的研究进展。     

广东连南汉族和瑶族儿童硫嘌呤甲基转移酶研究

目的本文对硫嘌呤甲基转移酶(Thiopurine S-methyltransferase,TPMT)在广东连南地区健康汉族儿童(n=87)和瑶族儿童(n=1 26)中的活性分布和4种常见TPMT基因突变的等位基因频率进行研究.方法采用高效液相色谱法测定红细胞的TPMT活性;采用等位基因特异性的PCR(allelespecific PCR,ASPCR)方法和限制性片断长度多态性(PCR-restrictionfragmentlength polymorphism,RFLP)的方法检测TPMT*2(G238C)、TPMT*3A(A719G/G460A)、TPMT*3B(G460A)和TPMT*3C(A719G)的等位基因频率.结果健康汉族儿童和瑶族儿童的TPMT活性都呈正态分布,活性的平均值分别为13.01±2.80U.ml-1pRBC和13.54±3.89U.ml-1 pRBC,两者的差异无显著性.在健康汉族儿童中只找到1例TPMT*3C杂合子(该汉族儿童的TPMT活性为12.36U.ml-1 pRBC),没有找到TPMT*2、TPMT*3A和TPMT*3B,汉族儿童总的TPMT基因突变频率是0.6%.在健康瑶族儿童中没有找到这几种突变.结论广东连南地区汉族和瑶族儿童TPMT的活性分布和总的TPMT基因突变频率没有显著性差异.     

环孢素、硝苯地平等5种肾移植受者常用药物对人体红细胞硫嘌呤甲基转移酶活性的影响

目的:研究肾移植受者中常与硫唑嘌呤(AZA)同时服用的药物如环孢素、泼尼松的活性代谢物氢化可的松、硝苯地平、卡托普利以及别嘌呤醇对硫嘌呤甲基转移酶(TPMT)活性的影响。方法:应用高效液相色谱法(HPLC)测定健康受试者红细胞TPMT活性,其中中等活性和正常活性受试者各8例,计算药物各浓度对应的平均TPMT活性抑制率及有抑制作用药物的平均IC_(50)值。结果:环孢素、氢化可的松、卡托普利以及别嘌呤醇对TPMT活性抑制作用较弱。硝苯地平能明显抑制TPMT的活性,中等活性组的平均IC_(50)值为(24±17)μg/mL,正常活性组的平均,IC_(50)值为(12±10)μg/mL。结论:硝苯地平能明显抑制TPMT活性,当硝笨地平与嘌呤类药物同时服用时,应警惕可能发生不良相互作用。     

中国哈萨克族人硫嘌呤甲基转移酶活性分布和基因多态性

目的 研究硫嘌呤甲基转移酶(TPMT)在中国哈萨克族的活性分布和4 种常见TPMT基因突变等位基因频率。方法 用高效液相色谱法测定TPMT 活性;用等位基因特异性聚合酶链反应检测TPMT*2;用限制性片段长度多态性 检测TPMT*3A、TPMT*3B和TPMT*3C的等位基因频率。结果 哈萨克族T PMT活性呈正态分布,活性的均值为(12．27±3．42)U·mL-1 Rbc,其中发现6 例TPMT*3C杂合子和2例TPMT*3A杂合子,总TPMT基因突变频率是1．2％。 结论 中国哈萨克族TPMT活性呈正态分布,总TPMT基因突变频率同汉族相 比差异无显著性。     

中国维吾尔族和哈萨克族人硫嘌呤甲基转移酶活性的分布

目的研究硫嘌呤甲基转移酶(TPMT)在中国新疆维吾尔族和哈萨克族人中的分布。方法运用改良的RP-HPLC法,测定红细胞中TPMT活性。结果160名维吾尔族成年人TPMT活性呈正态分布,活性均值为(11．57±3．52)U·mL-1 RBC (3．35-29．07 U·mL-1RBC)。327名哈萨克族成年人的TPMT活性呈正态分布,TPMT活性均值(12．27±3．42)U·mL-1 RBC (3．29-24．67 U·mL-1RBC)。在中国新疆维吾尔族和哈萨克族中没有发现酶缺乏者,TPMT活性不存在性别差异。维吾尔族、哈萨克族成年人与汉族TPMT活性相比较,两者差异无统计学意义。结论中国新疆维吾尔族和哈萨克族人TPMT活性呈正态分布。     

贵州地区急性淋巴细胞白血病儿童TPMT、NUDT15基因多态性与6-MP耐受性分析

目的 观察贵州地区ALL儿童TPMT、NUDT15基因多态性,探讨其与6-MP耐受性的关系。方法 收集贵阳市儿童医院血液科住院的贵州地区ALL儿童。Sanger法检测患者NUDT15c.415C>T和TPMT*2、TPMT*3A、TPMT*3B、TPMT*3C基因型。所有ALL儿童均按CCLG-2008方案化疗,每周1次监测血常规及肝肾功能。根据2016新编WHO化疗药物毒性反应分度标准,出现Ⅲ～Ⅳ度与6-MP相关的毒性反应,称为6-MP不耐受(除外感染、其他药物影响)。分析TPMT、NUDT15基因多态性与6-MP不耐受的相关性。结果 共纳入患者60例,检测到TPMT突变(中间代谢型)3例(5%),正常代谢型57例(95%)。NUDT15基因CT型12例(20%),TT型1例(1.7%),CC型(野生型) 47例(78.3%)。NUDT15基因突变率21.7%(13/60)显著高于TPMT基因突变率5%(3/60),差异有统计学意义(P=0.007)。TPMT突变型3例均发生6-MP不耐受(100%),NUDT15突变型13例中11例发生6-MP不耐受(84.6%)。结论 TP...     

TPMT遗传多态性对硫嘌呤类药物疗效和毒性影响的研究进展

目的:总结硫嘌呤甲基转移酶(TPMT)遗传多态性对硫嘌呤类药物疗效和毒性影响的研究进展,为该药的个体化应用提供参考。方法:通过检索Pub Med和相关专业学术期刊全文数据库近10年来有关TPMT遗传多态性对硫嘌呤类药物疗效和毒性影响的研究文献,对TPMT遗传药理学研究进展作一整理归纳。结果和结论:TPMT是被研究得最早也是最多的一个硫嘌呤类药物代谢酶。TPMT遗传多态性和酶活性的个体差异可以部分解释患者服用硫嘌呤类药物后疗效和不良反应的不同。但目前其与硫嘌呤类药物所致的不良反应之间的关系尚没有统一的结论。对于TPMT遗传多态性对硫嘌呤类药物个体化应用的影响有待于多中心大样本的前瞻性研究以证实。     

中国肾移植患者红细胞内嘌呤类药物活性代谢物6-硫鸟嘌呤核苷酸浓度监测及影响因素分析

目的：研究服用硫唑嘌呤（AZA）中国肾移植患者红细胞（RBC）内活性代谢物6-硫鸟嘌呤核苷酸（6-TGNs）分布特征及影响因素，为临床合理应用嘌呤类药物提供依据。方法：以89例中国肾移植患者为研究对象，关联分析年龄、性别、体质量、AZA剂量和TPMT活性对RBC内6-TGNs浓度的影响，并应用SPSS v20.0软件进行多元线性回归分析。结果：89例中国肾移植患者RBC内6-TGNs浓度呈非正态分布（P<0.000 1），6-TGNs浓度中位数为167.60（四分位间距，108.10~300.80） pmol/8×10⁸ RBC，个体间差异约24.3倍。关联分析显示患者年龄、性别、体质量、TPMT活性对6-TGNs浓度均无显著影响（P>0.05）；而AZA剂量与6-TGNs浓度间呈显著正相关性（r_s=0.307 1，P<0.01）。多元线性回归分析显示，RBC内6-TGNs浓度与AZA剂量间呈显著正相关（P<0.001），与TPMT活性呈显著负相关（P<0.05）。结论：AZA剂量和RBC内TPMT活性协同影响嘌呤类药物活性代谢物6-TGNs浓度，进而影响该类药物临床疗效和毒性反应。     

Relationships between thiopurine S-methyltransferase polymorphism and azathioprine-related adverse drug reactions in Chinese renal transplant recipients

Objective  To systematically investigate the relationships between thiopurine S-methyltransferase (TPMT) polymorphisms and azathioprine-related adverse drug reactions in patients with kidney transplantation. Methods  Erythrocyte TPMT activity of 150 patients with kidney transplantation and AZA therapy was determined by HPLC. The frequency of four common TPMT mutant alleles, TPMT*2, *3A, *3B, and *3C was determined by allele-specific PCR and PCR-restriction fragment length polymorphism (PCR-RFLP) analysis. Results  Thirty cases (20%) had stopped azathioprine medication or were on reduced dose due to azathioprine-related side effects. The TPMT activity range of cases who never experienced side effects was 16.63-68.25 U, the mean of the controls was 38.43 ± 11.59 U. The mean value of 12 cases with hematotoxicity was 23.50 ± 10.33 U, much lower than the control mean (P < 0.05). No significant difference between the mean value of 18 cases with hepatotoxicity and the control mean (P > 0.05) was seen. No case with TPMT deficiency was found in all patients studied, and TPMT*2, *3A, and *3B were not detected in any of them. TPMT*3C heterozygous alleles were found in 4.7% (seven cases) of these patients, all seven cases had intermediate TPMT activity, and the mean was 16.75 ± 2.09 U, much lower than other TPMT wild-type patients (P < 0.05). In the seven TPMT*3C patients, four cases experienced side effects (hematotoxicity, n = 2; hepatotoxicity, n = 2). Conclusions  This study demonstrates that TPMT activity is reduced in patients with TPMT*3C mutation. AZA-induced hematotoxicity is related to the reduced TPMT activity.     

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。     

Thiopurine S-methyltransferase phenotype-genotype correlation in hemodialyzed patients

Thiopurine S-methyltransferase (TPMT) is a cytosolic enzyme, catalyzing S-methylation of thiopurine drugs. TPMT exhibits autosomal codominant polymorphism. Patients carrying a variant genotype have low TPMT activity, and produce elevated levels of 6-thioguanine nucleotides (6-TGN) in their red blood cells (RBC). 6-TGN accumulation may result in azathioprine (AZA)-induced bone marrow myelosuppression in the course of treatment with the drug in a standard dosage regimen in patients following renal transplantation. In the current study, TPMT activity (phenotype) and genotype were determined in dialyzed patients, qualified for renal transplantation. TPMT activity was measured in RBC after dialysis by HPLC method. Patients were genotyped for TPMT *2, *3A and *3C variant alleles using PCR-RFLP and allele-specific PCR methods. TPMT activity ranged between 12.2 and 45.5 nmol 6-mMP/g Hb/h (median value 30.6). A significant correlation between TPMTphenotype and genotype was noted: the heterozygous patients (11.5%) demonstrated significantly lower mean TPMT activity as compared to the wild homozygotes (17 +/- 3.6 vs. 32.4 +/- 4.8 nmol 6-mMP/g Hb/h, p < 0.0003). No overlap in TPMT activity values between the group of heterozygous (range 12.2-20.6) and wild-type homozygous patients (range 22.7-45.5) was noted. TPMT activity, established after hemodialysis and TPMT genotyping results seem to be convergent in dialyzed patients, so both methods can be used for the identification of patients with lower TPMT activity. Such tests could be helpful in AZA dose individualization, and thus in reducing the risk of myelosuppression during AZA therapy following renal transplantation.     

Phenotype and genotype for thiopurine methyltransferase activity in the French Caucasian population: impact of age

Objective Thiopurine drugs are commonly used in pediatric patients for the treatment of acute leukemia, organ transplantation and inflammatory diseases. They are catabolized by the cytosolic thiopurine methyltransferase (TPMT), which is subject to a genetic polymorphism. In children, enzyme activities are immature at birth and developmental patterns vary widely from one enzyme to another. The present study was undertaken to evaluate erythrocyte TPMT activity and the correlation between genotype and phenotype in different age groups from birth to adolescence and adulthood.Methods The study included 304 healthy adult blood donors, 147 children and 18 neonates (cord bloods). TPMT activity was measured by liquid chromatography, and genotype was determined using a polymerase chain reaction reverse dot-blot analysis identifying the predominant TPMT mutant alleles (TPMT*3A, TPMT*3B, TPMT*3C, TPMT*2).Results There was no significant difference in TPMT activity between cord bloods (n=18) and children (n=147) (17.48±4.04 versus 18.62±4.14 respectively, P=0.424). However, TPMT was significantly lower in children than in adults (19.34±4.09) (P=0.033). In the whole population, there were 91.9% homozygous wild type, 7.9% heterozygous mutants and 0.2% homozygous mutants. The frequency of mutant alleles was 3.0% for TPMT*3A, 0.7% for TPMT*2 and 0.4% for TPMT*3C.Conclusion No impact of child development on TPMT activity could be evidenced, suggesting that TPMT activity is already mature at birth. The difference between children and adults was low with reduced clinical impact expected. When individual TPMT activity was compared with genotype, there was an overlapping region where subjects (4.5%, 12 adults, 9 children) were either homozygous wild type or heterozygous, with a TPMT activity below the antimode value. This result highlighted the importance of measuring TPMT activity to detect all patients at risk of thiopurine toxicity.     

Thiopurine methyltransferase activity and its relationship to the occurrence of rejection episodes in paediatric renal transplant recipients treated with azathioprine

AIMS: Azathioprine is a prodrug commonly used in combination therapy to prevent allograft rejection after renal transplantation. After conversion to 6-mercaptopurine, the drug is metabolized into 6-thioguanine nucleotides (6-TGN) and catabolized by thiopurine methyltransferase (TPMT), an enzyme under monogenic control. The aim of this study was to evaluate the inter- and intraindividual variability of red blood cell thiopurine methyltransferase and 6-TGN concentrations and their relationship to the clinical effects of azathioprine in paediatric patients. METHODS: In the present study, the inter- and intraindividual variations in red blood cell TPMT activity and 6-TGN concentrations and their relationship to the actions of azathioprine were evaluated during the first year after renal transplantation in 22 paediatric patients. RESULTS: 6-TGN concentration reached steady-state values after 6 months and correlated negatively with TPMT activity (P=0.004). Initial TPMT activity (median: 20.8 nmol h-1 ml-1, range 7.8-34.6) and 6-TGN concentration at steady-state (median: 80 pmol 8 x 10(8-1) cells, range not detected to 366) were not related to the occurrence of rejection episodes during the period of the study. In contrast, TPMT activity and the percentage difference in TPMT activity from the day of transplantation determined at month 1 were higher in the patients with rejection episodes by comparison with those that did not reject during the first 3 months or the first year following transplantation (P<0.005). CONCLUSIONS: We report a relationship between TPMT activity and occurrence of rejection in paediatric kidney transplant patients undergoing azathioprine therapy. These data suggest a link between high red blood cell TPMT activity and poor clinical outcome probably caused by rapid azathioprine catabolism.     

The impact of thiopurine s-methyltransferase polymorphism on azathioprine-induced myelotoxicity in renal transplant recipients

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 as a result of genetic polymorphism. Patients with intermediate or deficient TMPT 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 low enzyme activity. The purpose of this study was to explore the association between these polymorphisms and the occurrence of azathioprine adverse effects in 112 renal transplant recipients undergoing triple immunosuppressive therapy including azathioprine, cyclosporine, and prednisone. TPMT genetic polymorphism was determined using PCR-RFLP and allele-specific PCR methods. Azathioprine dose, leukocyte, erythrocyte, and platelet counts, graft rejection episodes, as well as cyclosporine levels were analyzed throughout the first year after organ transplantation. We found the frequency of leukopenia episodes (WBC < 4.0 x 10(9)/L) significantly higher in heterozygous patients (53.8%) compared with those with TPMT wild-type genotype (23.5%). One patient, who was a compound homozygote (3A/*3C), experienced severe azathioprine-related myelotoxicity each time after receiving the standard drug dose. Our results suggest that polymorphisms in TPMT gene may be responsible for approximately 12.5% of all leukopenia episodes in renal transplant recipients treated with azathioprine. Genotyping for the major TPMT variant alleles may be a valuable tool in preventing AZA toxicity and optimization of immunosuppressive therapy.     

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.     

Thiopurine S-methyltransferase pharmacogenetics: variant allele functional and comparative genomics

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. Genetic polymorphisms for TPMT are a major factor responsible for large individual variations in thiopurine toxicity and therapeutic effect. The present study investigated the functional effects of human TPMT variant alleles that alter the encoded amino acid sequence of the enzyme, TPMT*2, *3A, *3B, *3C and *5 to *13. After expression in COS-1 cells and correction for transfection efficiency, allozymes encoded by these alleles displayed levels of activity that varied from virtually undetectable (*3A,*3B and *5) to 98% (*7) of that observed for the wild-type allele. Although some allozymes had significant elevations in apparent Km values for 6-mercaptopurine and S-adenosyl-L-methionine (i.e. the two cosubstrates for the reaction), the level of enzyme protein was the major factor responsible for variation in activity. Quantitative Western blot analysis demonstrated that the level of enzyme protein correlated closely with level of activity for all allozymes except TPMT*5. Furthermore, protein levels correlated with rates of TPMT degradation. TPMT amino acid sequences were then determined for 16 non-human mammalian species and those sequences (plus seven reported previously, including two nonmammalian vertebrate species) were used to determine amino acid sequence conservation. Most human TPMT variant allozymes had alterations of residues that were highly conserved during vertebrate evolution. Finally, a human TPMT homology structural model was created on the basis of a Pseudomonas structure (the only TPMT structure solved to this time), and the model was used to infer the functional consequences of variant allozyme amino acid sequence alterations. These studies indicate that a common mechanism responsible for alterations in the activity of variant TPMT allozymes involves alteration in the level of enzyme protein due, at least in part, to accelerated degradation.     

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.     

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.