Distribution of TPMT risk alleles for thioupurine toxicity in the Israeli population

Role of Thiopurines in Pediatric Inflammatory Bowel Diseases: A Real-Life Prospective Cohort Study

OBJECTIVES

Use of thiopurines for inflammatory bowel diseases (IBDs) is declining in some parts of the world. We aimed to explore outcomes of thiopurines and predictors of response in a real-world prospective cohort of children with dose optimization.

METHODS

Children with IBD treated with thiopurines without biologics were enrolled. Dosing was guided by thiopurine S-methyltransferase-activity at baseline and by clinical response and toxicity at 4 months; 1 year into the study, therapeutic drug monitoring at 4 months was also considered in the decision making. The primary outcome was steroid-free remission without treatment escalation by 12 months (SFR), using the intention-to-treat approach.

RESULTS

A total of 129 children were included (74% Crohn disease [CD] and 26% ulcerative colitis [UC]). SFR was achieved in 37 (39%) CD and 13 (39%) UC patients, and SFR with normal erythrocyte sedimentation rate/C-reactive protein in 20 (21%) and 9 (27%), respectively. At 4 months, mean corpuscular volume/white blood cell ratio and Δ absolute neutrophil count weakly correlated with 6-thioguanine (r = 0.33, P = 0.02 and r = 0.32, P = 0.02, respectively). In CD, SFR was associated with 4-month median weighted Pediatric Crohn Disease Activity Index (2.5 [IQR 0-7.5] in responders vs 5 in nonresponders [0-12.5], P = 0.048) and Δabsolute neutrophil count (1.7 [IQR 0.7-4.1] vs 0.05 [-2.3-0.9]; P = 0.03). Mild drug-related adverse events were recorded in 30 children (22%), 3 required stopping the drug.

CONCLUSIONS

In this real-life prospective cohort using dose optimization, thiopurines were safe and effective in 21% of CD and 27% of UC patients, including normalization of C-reactive protein and erythrocyte sedimentation rate. Thiopurines remain a viable option in the treatment algorithm of mild-moderate pediatric IBD, especially in girls whose risk for lymphoma is lower.

Myasthenia gravis and azathioprine treatment: Adverse events related to thiopurine S-methyl-transferase (TPMT) polymorphisms

Azathioprine (AZA) is the most common immunosuppressive drug used to treat myasthenia gravis (MG). To analyses the prevalence of thiopurine S-methyl-transferase (TPMT) genotypes and their association with adverse events due to azathioprine therapy in MG patients. Allele-specific polymerase chain reaction (PCR) and PCR with restriction fragment length polymorphism (RFLP) analysis were carried out to determine the prevalence of the most common TPMT genotypes (*2, *3A, *3B and *3C) in 50 MG patients from Southern Brazilian. The frequency of adverse reactions due to azathioprine therapy was analysed and correlated with different genotypes groups. The prevalence of TPMT gene variants was 12%. The allelic frequency of variant TPMT*2 (C238G), TPMT*3A (G460A/A719G), TPMT*3B (G460A), and TPMT*3C (A719G) genotypes was 1, 3, 2 and 1%, respectively. Adverse events occurred in 44%, of MG patients, of which 86% were minor and 14% were major. One patient, who presented a major adverse event (bone marrow suppression), was homozygous for the TPMT*3A genotype. Our study estimated the prevalence of TPMT genotypes for Brazilian MG patients. The profile of TPMT genotypes was different from other Brazilian populations. Hardy-Weinberg equilibrium and allelic frequencies of TPMT*3A and TPMT*3B, respectively, were different than expected, a finding that suggests a possible founder effect. Major adverse events were statistically significant for TPMT genotypes compared to wild-type. Although TPMT genotype has been associated with AZA-related adverse events, since no statistically significant difference among wild-type and other TPMT genotypes for minor adverse events, our study supports the view that TPMT genotype alone is not enough to adequately personalise the AZA therapy in MG patients. In conclusion, these results were important to characterise the prevalence of TPMT gene variants in MG patients treated with AZA and correlate the adverse events of this therapy in a real-world outpatient clinic from Southern Brazil.

Comprehensive overview of the pharmacogenetic diversity in Ashkenazi Jews

BACKGROUND

Adverse drug reactions are a major concern in drug development and clinical therapy. Genetic polymorphisms in genes involved in drug metabolism and transport are major determinants of treatment efficacy and adverse reactions, and constitute important biomarkers for drug dosing, efficacy and safety. Importantly, human populations and subgroups differ substantially in their pharmacogenetic variability profiles, with important consequences for personalised medicine strategies and precision public health approaches. Despite their long migration history, Ashkenazi Jews constitute a rather isolated population with a unique genetic signature that is distinctly different from other populations.

OBJECTIVE

To provide a comprehensive overview of the pharmacogenetic profile in Ashkenazim.

METHODS

We analysed next-generation sequencing data from 5076 Ashkenazim individuals and used sequence data from 117 425 non-Jewish individuals as reference.

RESULTS

We derived frequencies of 164 alleles in 17 clinically relevant pharmacogenes and derived profiles of putative functional consequences, providing the most comprehensive data set of Jewish pharmacogenetic diversity published to date. Furthermore, we detected 127 variants with an aggregated frequency of 20.7% that were specifically found in Ashkenazim, of which 55 variants were putatively deleterious (aggregated frequency of 9.4%).

CONCLUSION

The revealed pattern of pharmacogenetic variability in Ashkenazi Jews is distinctly different from other populations and is expected to translate into unique functional consequences, especially for the metabolism of CYP2A6, CYP2C9, NAT2 and VKORC1 substrates. We anticipate that the presented data will serve as a powerful resource for the guidance of pharmacogenetic treatment decisions and the optimisation of population-specific genotyping strategies in the Ashkenazi diaspora.

Association Between Combined Presence of Hepatitis C Virus and Polymorphisms in Different Genes With Toxicities of Methotrexate and 6-Mercaptopurine in Children With Acute Lymphoblastic Leukemia

BACKGROUND

The aim of the present study is to determine the correlation of hepatitis C virus (HCV) infection and polymorphisms in different genes with toxicity of either methotrexate (MTX) or 6-mercaptopurine (6-MP) administered to children with acute lymphoblastic leukemia (ALL).

PROCEDURE

One hundred children with low-risk ALL, who were treated according to the St. Jude Total therapy XV, were recruited. The recruited children were receiving MTX and 6-MP during maintenance phase. Patients were excluded from the study if they had other types of leukemia. Genotyping analyses for the thiopurine methyltransferase (TPMT), methylenetetrahydrofolate reductase (MTHFR), and glutathione S-transferase (GST) genes were performed using a combination of polymerase chain reaction (PCR) and PCR-RFLP (where RFLP is restriction fragment length polymorphism) protocols. Relevant clinical data on adverse drug reactions were collected objectively (blinded to genotypes) from the patient medical records.

RESULTS

There was a significant correlation between the combined presence of HCV and TPMT*3B G460A gene polymorphisms and grades 2-4 hepatotoxicity as aspartate aminotransferase (AST) elevation (P < 0.04). The same observation was seen when comparing either the presence of HCV alone or the presence of the gene polymorphism alone. A significant association between the combined presence of HCV and MTHFR C677T polymorphism and grades 2-4 hepatotoxicity as alanine aminotransferase (ALT), AST, and alkaline phosphatase (ALP) elevation was observed (P values <0.001, 0.02, and 0.001, respectively). The presence of HCV infection had a significant negative effect on hepatic transaminases.

CONCLUSIONS

The present data support a role for combining analysis of genetic variation in drug-metabolizing enzymes and the presence of HCV in the assessment of specific drugs toxicities in multiagent chemotherapeutic treatment regimens.

Thiopurine S-methyltransferase (TPMT) activity is better determined by biochemical assay versus genotyping in the Jewish population

BACKGROUND

Thiopurine S-methyltransferase (TPMT) is a key enzyme that deactivates thiopurines, into their inactive metabolite, 6-methylmercaptopurine. Intermediate and low TPMT activity may lead to leukopenia following thiopurine treatment. The aim of this study was to determine TPMT activity and TPMT alleles (genotype-phenotype correlation) in Jews, aiming to develop an evidence-based pharmacogenetic assay for this population.

METHODS

TPMT activity was determined in 228 Jewish volunteers by high performance liquid chromatography. Common allelic variants in the Caucasian population [TPMT*2 (G238C), TPMT *3A (G460A and A719G), TPMT* 3B (G460A) and TPMT*3C (A719G)] were tested. Phenotype-genotype correlation was examined and discordant cases were fully sequenced to identify novel genetic variants.

RESULTS

Mean TPMT activity was 15.4 ± 4 U/ml red blood cells (range 1-34). Intermediate activity was found in 33/228 (14%) subjects and absent activity was found in one sample (0.4%). Only eight individuals (3.5% of the entire cohort and 24% of those with intermediate/low activity) were identified as carriers of a TPMT genetic variant, all of whom had the TPMT*3A allele. Sequencing the entire TPMT coding region and splice junctions in the remainder of the discordant cases did not reveal any novel variants.

CONCLUSION

Genotyping TPMT in Jews yields a much lower rate of variants than identified in the general Caucasian population. We conclude that a biochemical assay to determine TPMT enzymatic activity should be performed in Jews before starting thiopurine treatment in order to identify low activity subjects.

Thiopurine methyltransferase genotyping in Palestinian childhood acute lymphoblastic leukemia patients

BACKGROUND

The genetic polymorphism of thiopurine methyltransferase (TPMT) is well characterized in most populations. Four common polymorphic alleles are associated with impaired activity of the enzyme. These are TPMT*2 (238G>C), TPMT*3B (c.460G>A), TPMT*3A (c.460G>A and c.719A>G) and TPMT*3C (c.719A>G). The aim of the present study was to determine the frequency of TPMT polymorphisms and their association with the occurrence of adverse events, during 6-mercaptopurine therapy in pediatric acute lymphoblastic leukemic (ALL) patients in Gaza Strip.

METHODS

A total of 56 DNA samples from all pediatric ALL patients admitted to the pediatric hematology departments of Gaza strip hospitals were analyzed. Genomic DNA from peripheral blood leukocytes was isolated and the TPMT*2, TPMT*3B TPMT*3A and TPMT*3C allelic polymorphism was determined by PCR-RFLP and allele specific PCR technique.

RESULTS

No TPMT*2, *3B or *3C alleles were detected. Only one, out of 56 patients, was found heterozygous for the TPMT*3A allele. Thus, the frequency of TPMT*3A allele was calculated to be 0.89%. Fourteen patients of ALL were suffering from myelotoxicity during 6-MP therapy. From our results, no significant association could be established between clinical and laboratory data and/or the presence of the mutation in TPMT gene.

CONCLUSION

TPMT*3A was the only deficiency allele detected in our population with an allelic frequency of 0.89%. Other polymorphic alleles in TPMT gene, or factors other than TPMT polymorphisms may be responsible for the development of myelosuppression in cases that don't carry the investigated TPMT alleles (*2, *3A, *3B and *3C). Therefore, more studies are recommended to study such factors.

Frequency of thiopurine S-methyltransferase mutant alleles in indigenous and admixed Guatemalan patients with acute lymphoblastic leukemia

Thiopurine S-methyltransferase (TPMT) polymorphisms affect the enzyme's activity and are predictive for the efficacy and toxicity of thiopurine treatment of acute lymphoblastic leukemia (ALL), autoimmune diseases and organ transplants. Because inter-ethnic differences in the distribution of these polymorphisms have been documented, we sequenced the TMPT gene in 95 Guatemalans, yet identified no new alleles. We also determined the frequency of the TPMT 2, 3A, 3B and 3C alleles in 270 admixed and 177 indigenous pediatric patients with ALL and healthy subjects from Guatemala using TaqMan assays and DNA sequencing. Among the 447 subjects genotyped, 10.0 % of the ALL cases and 13.6 % of the healthy controls were heterozygous for one of the four TPMT variants screened. The genotype frequencies in ALL and control populations were 0.7 and 1.7 % for TPMT 1/ 2, 7.4 and 10 % for TPMT 1/3A, 0.3 and 0 % for TPMT 1/B, and 1.5 and 1.1 % for TPMT 1/C, respectively (p = 0.30). No statistically significant differences between admixed and indigenous ALL (p = 0.67) or controls (p = 0.41) groups were detected; however, 17 % of the admixed healthy group bore one TPMT mutant allele, and they have one of the highest reported frequencies of TPMT mutant allele carriers. Because of the clinical implications of these variants for therapeutic response, TPMT allele testing should be considered in all Guatemalan patients to reduce adverse side-effects from thiopurine drug treatments.

Toxicity of azathioprine: why and when? analysis of the prevalence of polymorphism in Joinville, SC, Brazil

CONTEXT: The use of thiopurine drugs such as azathioprine and 6-mercaptopurine has become quite common in the treatment of inflammatory bowel disease, transplantation and acute leukemias. Despite their effectiveness, these drugs are capable of causing drug-induced toxicity with the risk of death by myelosuppression. It is now known that these complications occur because of genetic polymorphisms of the thiopurinemethyltransferase (TPMT) enzyme, responsible for its metabolism. OBJECTIVE: To assess the prevalence of thiopurine methyltransferase polymorphisms in the population of Joinville, SC, Brazil. METHODS: We analyzed the frequency of four main allelic variants of the TPMT gene in 199 blood donors from Joinville, from February to April 2010. RESULTS: The normal allele ("wild-type") was found in 93.9% of subjects studied. TPMT variants were detected in 12 subjects (6.03%). CONCLUSIONS: From this study, it was estimated at 6% the risk of toxicity by the administration of azathioprine and 6-mercaptopurine to patients in Joinville.

Pre-analytic and analytic sources of variations in thiopurine methyltransferase activity measurement in patients prescribed thiopurine-based drugs: A systematic review

OBJECTIVES

Low thiopurine S-methyltransferase (TPMT) enzyme activity is associated with increased thiopurine drug toxicity, particularly myelotoxicity. Pre-analytic and analytic variables for TPMT genotype and phenotype (enzyme activity) testing were reviewed.

DESIGN AND METHODS

A systematic literature review was performed, and diagnostic laboratories were surveyed.

RESULTS

Thirty-five studies reported relevant data for pre-analytic variables (patient age, gender, race, hematocrit, co-morbidity, co-administered drugs and specimen stability) and thirty-three for analytic variables (accuracy, reproducibility). TPMT is stable in blood when stored for up to 7 days at room temperature, and 3 months at -30°C. Pre-analytic patient variables do not affect TPMT activity. Fifteen drugs studied to date exerted no clinically significant effects in vivo. Enzymatic assay is the preferred technique. Radiochemical and HPLC techniques had intra- and inter-assay coefficients of variation (CVs) below 10%.

CONCLUSION

TPMT is a stable enzyme, and its assay is not affected by age, gender, race or co-morbidity.

High-resolution DNA melting analysis in clinical research and diagnostics

Among nucleic acid analytical methods, high-resolution melting analysis is gaining more and more attention. High-resolution melting provides simple, homogeneous solutions for variant scanning and genotyping, addressing the needs of today's overburdened laboratories with rapid turnaround times and minimal cost. The flexibility of the technique has allowed it to be adopted by a wide range of disciplines for a variety of applications. In this review we examine the broad use of high-resolution melting analysis, including gene scanning, genotyping (including small amplicon, unlabeled probe and snapback primers), sequence matching and methylation analysis. Four major application arenas are examined to demonstrate the methods and approaches commonly used in particular fields. The appropriate usage of high-resolution melting analysis is discussed in the context of known constraints, such as sample quality and quantity, with a particular focus placed on proper experimental design in order to produce successful results.

Genetic analysis of thiopurine methyltransferase polymorphism in the Jordanian population

This study provides the first analysis of the TPMT mutant allele frequency in a sample of the Jordanian population and indicates that TPMT*3A is the most common allele in Jordanian subjects.

PURPOSE

thiopurine methyltransferase TPMT catalyses the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathiopurine. Thiopurine methyltransferase (TPMT) polymorphisms are the major determinants of interindividual differences in the severe haematological toxicity of 6-mercaptopurine. Several variants in the TPMT gene have been identified that correlate with a low activity phenotype. Four variant alleles, TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C, are responsible for over 80% of the low or undetectable enzyme activity. The allelic frequency of TPMT variants has been established in many populations.

METHODS

In this study, the frequencies of four (TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C) variants were investigated in 169 healthy Jordanian men (18-45 years of age). Single nucleotide polymorphisms (SNPs) were genotyped using the Sequenom MassARRAY technology (Sequenom; San Diego, CA, USA).

RESULTS

TPMT*3A and TPMT*3C were the only deficiency alleles detected in the Jordanian population with an allele frequency of 0.59% and 0.30% respectively. The TPMT*3A allele frequency is found to be lower than in the European Caucasian population.

CONCLUSION

TPMT*3A and TPMT*3C were the only deficiency alleles detected in the Jordanian population with an allele frequency of 0.59% and 0.30% respectively. The TPMT*3A allele frequency is found to be lower than in the European Caucasian population.