Frequency of TPMT alleles in Indian patients with acute lymphatic leukemia and effect on the dose of 6-mercaptopurine

Impact of pharmacogenomics in achieving personalized/precision medicine in the clinical setting: a symposium report

The Indo-Swiss symposium on pharmacogenomic strategies for the implementation of personalized medicine was conducted as part of the Jawaharlal Institute of Postgraduate Medical Education and Research Integrated Pharmacogenomics Program in Puducherry, India, on 19 November 2022. The symposium was conducted in hybrid mode. The theme of symposium was the impact of pharmacogenomics on the achievement of personalized medicine/precision medicine in the clinical setting. The symposium sought to promote interaction among the participants to initiate future collaborative research projects. The symposium also served as a platform for young researchers to present their research findings as posters to the audience.

NUDT15 c.415C>T Polymorphism Predicts 6-MP Induced Early Myelotoxicity in Patients with Acute Lymphoblastic Leukemia Undergoing Maintenance Therapy

PURPOSE

Severe myelosuppression in patients with acute lymphoblastic leukemia (ALL) undergoing 6-MP-based maintenance therapy is attributed to TPMT gene polymorphisms, which is rare in Asian populations. This study aims to evaluate the role of selected polymorphisms in NUDT15, ITPA, and MRP4 genes in addition to TPMT in predicting 6-MP intolerance during ALL maintenance therapy.

PATIENTS AND METHODS

We screened for the presence of NUDT15*3 (c.415 C>T, rs116855232); MRP4 c.2269 C>T (rs3765534), ITPA c.94 C>A (rs1127354) polymorphisms in addition to TPMT *2 (rs1800462), *3A (*3B and *3C; rs1800460 and rs1142345) in ALL patients with documented severe neutropenia (cohort-1; n=42). These polymorphisms were then screened in a prospective cohort of ALL patients (cohort-2; n=133) and compared with 6-MP dose reduction, early/late myelotoxicity.

RESULTS

Nineteen (45%) patients in cohort-1 and 18 (14%) in cohort-2 had NUDT15 c.415 C>T variant while 4 (3%) patients in cohort-2 had TPMT*3C variant. Five (12%) in cohort-1 and 30 (24%) in cohort-2 had ITPA c.94 C>A variant while 9 (22%) and 15 (12%) had MRP4 c.2269 C>T variant in cohorts-1 and 2, respectively. All in cohort-1 and 36 (27%) in cohort-2 had severe myelotoxicity. Twenty-eight patients (66.6%) in cohort-1 and 40 (30%) patients in cohort-2 had significant 6-MP dose reduction. NUDT15 c.415 C>T variant explained severe myelotoxicity in 63% and 33% in cohort 1 and 2. TPMT*3C and ITPA c.94 C>A variants also explained myelotoxicity in cohort-2 (Median ANC: 376 vs 1014 mm3; p=0.04 and 776 vs 1023 mm3; p=0.04 respectively). NUDT15 c.415 C>T polymorphism explained significant myelotoxicity (507 vs 1298 mm3; p<0.0001) in the multivariate analysis as well (β=-0.314, p<0.0001).

CONCLUSION

NUDT15 c.415 C>T (15*3), TPMT*3C, as well as ITPA c.94 C>A and MRP4 c.2269 C>T polymorphisms explain hematotoxicities. Preemptive genotype-based (NUDT15*3, TPMT, ITPA c.94 C>A) 6-MP dosing could improve the outcome after maintenance therapy.

Prevalence of polymorphisms in thiopurine metabolism and association with adverse outcomes: a South Asian region-specific systematic review and meta-analysis

Background: Prevalence and impact of thiopurine S-methyltransferase (TPMT) and Nudix hydrolase (NUDT15) minor allele frequencies in South Asian population is unclear.Methods: We searched PubMed and Embase with keywords-TPMT and NUDT15 combined with South Asian countries. We included studies reporting frequency of TPMT and NUDT15 polymorphisms. We estimated the pooled prevalence of TPMT and NUDT15 polymorphisms and their impact on pooled odds ratio of adverse events with thiopurines.Results: We included 26 studies in our analysis. The pooled prevalence of NUDT15 and TPMT polymorphisms was 16.5% (95% CI: 13.09-20.58) and 4.57% (95% CI: 3.66-5.68), respectively. In patients with adverse effects, the pooled prevalence of NUDT15 and TPMT polymorphism was 49.51% (95% C.I. 21.69-77.64) and 9.47% (95% C.I. 5.39-16.11), respectively. The odds ratio (OR) of adverse events with presence of TPMT polymorphisms was 3.65 (95% C.I., 1.43-9.28). The pooled OR for adverse events in presence of NUDT15 polymorphism was 12.63 (95% C.I., 3.68-43.26).Conclusion: NUDT15 were reported more frequently than the TPMT polymorphisms in South Asian population and were more frequently associated with adverse events. These findings may have implications for preemptive testing amongst South Asian population and immigrants prior to starting thiopurines.

NUDT15 polymorphism explains serious toxicity to azathioprine in Indian patients with chronic immune thrombocytopenia and autoimmune hemolytic anemia: a case series

OBJECTIVES

Azathioprine (AZA) is a commonly used immunosuppressant in patients with autoimmune diseases. The toxic side effect to AZA (myelosuppression, hair loss, and oral ulcers) are highly unpredictable which can be life threatening if not identified earlier and dose adjustments made or the drug is withdrawn.

CASE PRESENTATION

Here we report a case series of five patients with severe toxicity while on treatment with AZA for autoimmune hemolytic anemia (n=1) and Immune thrombocytopenia (n=4). The common thiopurine methyltransferase (TPMT) variants (TPMT*2, *3A, *3B) were not present in these patients. However, all these patients had the NUDT15 415C>T variant that has been reported to explain serious toxicity to thioguanine in Asian patients.

CONCLUSIONS

Our report suggests pre-emptive genotype-based dosing of AZA could reduce adverse toxicity and hence better outcome.

The Roles of Common Variation and Somatic Mutation in Cancer Pharmacogenomics

Cancer pharmacogenomics is the science concerned with understanding genetic alterations and its effects on the pharmacokinetics and pharmacodynamics of anti-cancer drugs, with the aim to provide cancer patients with the precise medication that will achieve a good response and cause low/no incidence of adverse events. Advances in biotechnology and bioinformatics have enabled genomic research to evolve from the evaluation of alterations at the single-gene level to studies on the whole-genome scale using large-scale genotyping and next generation sequencing techniques. International collaborative efforts have resulted in the construction of databases to curate the identified genetic alterations that are clinically significant, and these are currently utilized in clinical sequencing and liquid biopsy screening/monitoring. Furthermore, countless clinical studies have accumulated sufficient evidence to match cancer patients to therapies by utilizing the information of clinical-relevant alterations. In this review we summarize the importance of germline alterations that act as predictive biomarkers for drug-induced toxicity and drug response as well as somatic mutations in cancer cells that function as drug targets. The integration of genomics into the medical field has transformed the era of cancer therapy from one-size-fits-all to cancer precision medicine.

Prevalence of TPMT, ITPA and NUDT 15 genetic polymorphisms and their relation to 6MP toxicity in north Indian children with acute lymphoblastic leukemia

PURPOSE

Toxicity of 6-Mercaptopurine (6MP) is related to single nucleotide polymorphism (SNP) in genes coding for metabolizing enzymes, with TPMT analysis being recommended prior to maintenance therapy. However, ITPA and NUDT15 polymorphisms appear more important in the Asian population.

METHOD

In this study 63 consecutive patients with ALL, entering maintenance phase of therapy, were evaluated for TPMT, ITPA and NUDT15 polymorphisms by PCR RFLP and confirmed by sequencing. Hematological and hepatic toxicities were monitored for 36 weeks. The groups with and without any of the three studied polymorphisms (Risk SNP + and Risk SNP-) were compared.

RESULTS

Eighteen (28.6%) patients had major polymorphisms, 17 being heterozygous. ITPA(198CA): 11(17.5%); NUDT (415CT): 6(9.5%) and TPMT*3C: in 2(3.1%). Mean cumulative dose of 6MP was lower: 10927 mg/m² in group with one of the polymorphisms compared to 12533 mg/m² in the group without a polymorphism (p = 0.009). The group with Risk SNP + tolerated lesser weeks of full-dose 6MP chemotherapy (20.81 vs 30.40 weeks; p = 0.001). Risk of neutropenia > 3 weeks was pronounced in Risk SNP + group. The individual TPMT, ITPA and NUDT15 polymorphism subgroups had similar cumulative 6MP dose and chemotherapy interruptions. There was no difference in the average cumulative dose of methotrexate in the two groups. No significant hepatotoxicity was noted.

CONCLUSION

Polymorphisms in ITPA and NUDT15 have a greater prevalence in the north Indian population. Patients with these SNPs tolerate lower doses of 6MP.

Thiopurine metabolite level and toxicity in Indians with inflammatory bowel disease

Background and Aim

A lower dose requirement and higher toxicity of thiopurine is reported in Asian patients with inflammatory bowel disease (IBD) as compared with Caucasian patients. These reports are based on thiopurine methyltransferase measurement studies rather than metabolite estimation.We studied the utility of thiopurine metabolite estimation in Indian patients with IBD and compared dose and toxicity with Asian and Caucasian patients.

Methods

In this prospective study, 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine levels were determined by HPLC in 76 IBD patients treated with thiopurines. The levels were correlated with dose, disease activity, and toxicity. The dose-related metabolite levels and toxicity were compared with Caucasian and Asian patients reported in literature.

Results

Of the 76 patients (32 women, mean age: 35.9 [SD: 14.54] years, 36 Crohn's disease and 40 ulcerative colitis), 1 non-compliant patient had undetectable level of metabolites. Of the 75 patients, 21(28%) had therapeutic level of 6-TGN, 37(49%) had subtherapeutic level and 17(23%) had supratherapeutic level. The 6-methylmercaptopurine levels ranged up to 4971 pmol/8 × 10⁸ red blood cells. Six (8%) patients showed toxicity. Thiopurine dose was optimized in 20 (26.31%) patients. Dose-based metabolite levels were comparable to Asian and Caucasian patients. The toxicity (8%) observed in our patients was less than that reported (12-39%).

Conclusion

Half of the patients in this study had low and a quarter had high 6-TGN levels. One-fourth of the patients needed dose modification. The dose-based metabolite levels were comparable and the toxicity was less than that reported in Asian and Caucasian patients.

Analysis of Thiopurine S-Methyltransferase Deficient Alleles in Acute Lymphoblastic Leukemia Patients in Mexican Patients

BACKGROUND AND AIMS

It has been demonstrated that heterozygote and homozygote thiopurine S-methyltransferase (TPMT) mutant allele carriers are at high risk to develop severe and potentially fatal hematopoietic toxicity after treatment with standard doses of 6-mercaptopurine (6-MP) and methotrexate (MX). Those drugs are the backbone of acute lymphoblastic leukemia (ALL) and several autoimmune disease treatments. We undertook this study to determine the frequency of the TPMT deficient alleles in children with ALL and non-ALL subjects from Mexico City and Yucatan, Mexico.

METHODS

We included 849 unrelated subjects, of which 368 ALL children and 342 non-ALL subjects were from Mexico City, and 60 ALL cases and 79 non-ALL individuals were from Yucatan. Genotyping of the rs1800462, rs1800460 and rs1142345 SNPs was performed by 5'exonuclease technique using TaqMan probes (Life Technologies Foster City, CA).

RESULTS

The mutant TPMT alleles were present in 4.8% (81/1698 chromosomes) and only 0.2% were homozygote TPMT*3A/TPMT*3A. We did not find statistically significant differences in the distribution of the mutant alleles between patients from Mexico City and Yucatan in either ALL cases or non-ALL. Nonetheless, the TPMT*3C frequency in ALL patients was higher than non-ALL subjects (p = 0.03). To note, the null homozygous TPMT*3A/TPMT*3A genotype was found in 2.5% of the non-ALL subjects.

CONCLUSIONS

TPMT mutant alleles did not exhibit differential distribution between both evaluated populations; however, TPMT*3C is overrepresented in ALL cases in comparison with non-ALL group. Assessing the TPMT mutant alleles could benefit the ALL children and those undergoing 6-MP and MX treatment.

Nucleoside diphosphate-linked moiety X-type motif 15 C415T variant as a predictor for thiopurine-induced toxicity in Indian patients

BACKGROUND AND AIM

Interindividual variation seen in the thiopurine metabolism is attributed to the genetic variant in thiopurine methyltransferase (TPMT) gene leading to myelosuppression. In Asians, the thiopurine-induced toxicity is not completely explained by TPMT variants. Literature indicates that a newer genetic variant in nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene is associated with thiopurine intolerance. We aimed to determine the risk allele frequency of NUDT15 genetic variant and its association with thiopurine-induced toxicity in Indian patients.

METHODS

In this pilot study, 69 patients on thiopurine therapy were analyzed. The frequencies of thiopurine-induced leukopenia were recorded. NUDT15 (C415T) and TPMT (*2, *3A, *3B, and *3C) genotyping was performed using amplification refractory mutation system-polymerase chain reaction and restriction fragment length polymorphism technique. Results were validated by DNA sequencing.

RESULTS

The NUDT15 CC, CT, and TT genotypes were found to be 86.9%, 11.5%, and 1.5%, respectively, whereas TPMT genetic variants were absent. Of 60 patients without NUDT15 variant, none developed leukopenia, whereas of nine patients with NUDT15 variant, six developed leukopenia (P-value < 0.0001). The mean thiopurine dose of 1.01 and 0.73 mg/kg/day for patients with wild and mutant NUDT15 alleles, respectively, was statistically significant (P < 0.01). The sensitivity and specificity for NUDT15 variant were 100% and 95.2%, respectively.

CONCLUSIONS

The NUDT15 risk allele frequency was 7.2%. There are 6/69 (8.7%) patients who developed leukopenia and harbored NUDT15 variant, thus showing a strong association for thiopurine-induced toxicity. Hence, NUDT15 genotyping may be considered before thiopurine therapy in Indian patients.

Clinical implication of thiopurine methyltransferase polymorphism in children with acute lymphoblastic leukemia: A preliminary Egyptian study

Background:

6-mercaptopurine (6-MP) is an essential component of pediatric acute lymphoblastic leukemia (ALL) maintenance therapy. Individual variability in this drug-related toxicity could be attributed in part to genetic polymorphism thiopurine methyltransferase (TPMT).

Aim:

To investigate the frequency of common TPMT polymorphisms in a cohort of Egyptian children with ALL and the possible relation between these polymorphisms and 6-MP with short-term complications.

Materials and Methods:

This study included 25 children. Data related to 6-MP toxicity during the maintenance phase were collected from the patients’ files. DNA was isolated and genotyping for TPMT G460A, and A719G mutations were performed by polymerase chain reaction-restriction fragment length polymorphism.

Results:

Twenty (80%) of the included 25 patients had a polymorphic TPMT allele. TPMT*3A was the most frequent (14/25, 56%), 8 patients were homozygous and 6 were heterozygous. TPMT*3C mutant allele was found in 4 patients (16%) in the heterozygous state while 2 patients (8%) were found to be heterozygous for TPMT*3B mutant allele. TPMT mutant patients, especially homozygous, were at greater risk of 6-MP hematological toxicity without significant difference regarding hepatic toxicity.

Conclusions:

TPMT polymorphism was common among the studied group and was associated with increased risk of drug toxicity. A population-based multi-center study is required to confirm our results.

Asia-Pacific consensus statements on Crohn's disease. Part 2: Management

The Asia Pacific Working Group on Inflammatory Bowel Disease was established in Cebu, Philippines, at the Asia Pacific Digestive Week conference in 2006 under the auspices of the Asian Pacific Association of Gastroenterology (APAGE) with the goal of developing best management practices, coordinating research and raising awareness of IBD in the region. The consensus group previously published recommendations for the diagnosis and management of ulcerative colitis (UC) with specific relevance to the Asia-Pacific region. The present consensus statements were developed following a similar process to address the epidemiology, diagnosis and management of Crohn's disease (CD). The goals of these statements are to pool the pertinent literature specifically highlighting relevant data and conditions in the Asia-Pacific region relating to the economy, health systems, background infectious diseases, differential diagnoses and treatment availability. It does not intend to be all-comprehensive and future revisions are likely to be required in this ever-changing field.

TPMT Polymorphism: When Shield Becomes Weakness

Thiopurine methyltransferase (TPMT) is a cytoplasmic transmethylase present in both prokaryotes and eukaryotes. In humans, it shows its presence in almost all of the tissues, predominantly in liver and kidney. TPMT is one of the important metabolic enzymes of phase II metabolic pathway and catalyzes methylation of thiopurine drugs such as azathioprine, 6-thioguanine and 6-mercaptopurine, which are used to treat patients with neoplasia and autoimmune disease as well as transplant recipients. In this sense, TPMT acts as shield against toxic effect of these drugs. Pharmacogenomic studies revealed that genetic polymorphism in TPMT is responsible for variable and, in some cases, adverse drug reaction. Those human groups who carry variants of TPMT (i.e., [Formula: see text], [Formula: see text], [Formula: see text]) are at high risk, because they are unable to metabolize thiopurine drugs thus becoming a weakness of patients against these drugs. Keeping in the mind the importance of TPMT, this review discusses the existence and distribution of various TPMT variants throughout different ethnic groups and risk of adverse drug reactions to them, and how they can avoid this risk of side effects. The review also highlighted factors responsible for variable reactions of TPMT, how this TPMT polymorphism can be considered in drug designing process to avoid toxic effects, designing precautions against them and more importantly designing personalized medicine.

Thiopurine methyltransferase polymorphisms in children with acute lymphoblastic leukemia

Introduction:

Acute lymphoblastic leukemia (ALL) is the most common malignancy in children. 6-mercaptopurine (6-MP) and methotrexate are backbone drugs for maintenance phase of treatment. Purine Analogs 6-MP/6-thioguanine/azathiopurine are metabolized to its inactive form by the enzyme thiopurine methyltransferase (TPMT). Ninety percent of the population harbor wild type on both alleles (TPMT wild/wild), 10% are heterozygous, that is, one allele is mutant (TPMT wild/mutant) and 0.3% are homozygous, that is, both allele are mutant (TPMT mutant/mutant). In heterozygous and homozygous variant, activity of enzyme is low, leading to a higher incidence of toxicity (myelosuppression).

Aim:

The primary objective was to access the polymorphism of the enzyme, TPMT, in Children with ALL. Secondary objective was to correlate TPMT genotype with 6-MP toxicities.

Materials and Methods:

Seventy-two children with newly diagnosed ALL during first maintenance phase were serially enrolled after obtaining consent. Five ml of peripheral blood was drawn and DNA extracted. TPMT 2 polymorphisms were performed using Allele specific polymerase chain reaction (PCR) and TPMT 3B and 3C are performed by PCR-restriction fragment length polymorphism.

Results:

Sixty-nine children of 72 (95.8%) were wild for TPMT polymorphism and 3 (4.2%) were heterozygous for TPMT. Among the heterozygous variant one each (33.3%) were heterozygous for 2A, 3A, 3C. Febrile neutropenia was the most common toxicity in both wild and heterozygous group.

Conclusion:

The frequency of TPMT polymorphisms in children with ALL is 4.2%. Heterozygous variant is this study are one each (33%) of 2A, 3A, 3C.

Pharmacogenetics of childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the major pediatric cancer in developed countries. Although treatment outcome has improved owing to advances in chemotherapy, there is still a group of patients for which therapy fails while some patients experience severe toxicity. In the last few years, several pharmacogenetic studies have been performed to search for markers of outcome and toxicity in pediatric ALL. However, to date, TPMT is the only pharmacogenetic marker in ALL with clinical guidelines for drug dosing. In this article, we will provide an overview of the most important findings carried out in pharmacogenetics for pediatric ALL, such as the interest drawn by methotrexate transporters in the context of methotrexate treatment. Even if most of the studies are centered on coding genes, we will also point to new approaches focusing on noncoding regions and epigenetic variation that could be interesting for consideration in the near future.

Prevalence of TPMT polymorphism in Indian patients requiring immunomodulator therapy and its clinical significance

BACKGROUND

Thiopurine methyltransferase (TPMT) enzyme plays a key role in the metabolism of azathioprine/6-mercaptopurine (6-MP). Mutations in the enzyme lead to generation of excess thioguanine, which causes suppression of various cell lineages, especially neutrophils. Data on the prevalence of TPMT polymorphism are available from Western and some Asian countries; such data from India are sparse.

AIMS

The aim of this research is to study the prevalence of TPMT mutation in Indian patients requiring immunomodulator therapy and its relation to the development of neutropenia on azathioprine therapy.

METHODS

In this retrospective study, data of all patients who underwent TPMT genotyping by PCR-RFLP and allele-specific PCR prior to immunomodulator therapy were analyzed. The frequency of on-treatment development of neutropenia (total neutrophil count <1,500 per cubic millimeters) was noted.

RESULTS

Data were available on 126 patients (mean age, 42 [SD 13.6] years; 73 men and 53 women). The disease indications included ulcerative colitis (61), Crohn's disease (43), indeterminate colitis (1), autoimmune hepatitis (16), and others (5). TPMT genotype was wild in 120 patients (95.23 %) and heterozygous in 6 patients (4.77 %); no patient had homozygous mutation. Seven of 87 patients (6.8 %) who received azathioprine developed neutropenia; blood counts normalized on cessation of the drug in all. The incidence of neutropenia in patients with wild type was 6/84 (7.14 %) and with heterozygous type 1/3 (33 %) (p = 0.5764).

CONCLUSION

Nearly 5 % of this population of patients requiring immunomodulator therapy was heterozygous carriers of the TPMT gene. Neutropenia was equally common in patients without and with the mutation.

Methylenetetrahydrofolate reductase gene haplotypes affect toxicity during maintenance therapy for childhood acute lymphoblastic leukemia in Japanese patients

Abstract The aim of this study was to investigate the influence of daily 6-mercaptopurine (6-MP) and low-dose weekly methotrexate (MTX) combination treatment and methylenetetrahydrofolate reductase (MTHFR) haplotypes on toxicity during maintenance therapy in Japanese childhood acute lymphoblastic leukemia (ALL). We retrospectively analyzed the MTHFR C677T and A1298C polymorphisms and influence of haplotypes on toxicity in 73 patients. Patients with the MTHFR 677TT and 677CT + 1298AC were associated with severe liver toxicity (p = 0.014, odds ratio [OR] = 3.82, 95% confidence interval [CI] = 1.27-11.46) and more rapid onset of liver toxicity (p = 0.010). Patients with MTHFR 677TT and 677CT + 1298AC were associated with lower frequency of 6-MP and MTX dose reduction due to leukopenia (p < 0.05). No difference was observed in average drug doses in the MTHFR genotypes. In conclusion, the MTHFR C677T and A1298C haplotypes might be useful for monitoring adverse effects in childhood ALL maintenance therapy in Japanese patients.

Indian Society of Gastroenterology consensus on ulcerative colitis

In 2010, the Indian Society of Gastroenterology's Task Force on Inflammatory Bowel Diseases undertook an exercise to produce consensus statements on ulcerative colitis. This consensus, produced through a modified Delphi process, reflects our current understanding of the definition, diagnostic work up, treatment and complications of ulcerative colitis. The consensus statements are intended to serve as a reference point for teaching, clinical practice, and research in India.

The activity of the inosine triphosphate pyrophosphatase affects toxicity of 6-mercaptopurine during maintenance therapy for acute lymphoblastic leukemia in Japanese children

The association between inosine triphosphate pyrophosphatase (ITPA) activity and toxicity of 6-mercaptopurine (6-MP) was retrospectively evaluated in 65 Japanese children with acute lymphoblastic leukemia (ALL). Patients with an ITPA activity of less than 126 μmol/h/gHb presented with hepatotoxicity more frequently than those with higher ITPA activity (p<0.01). The average 6-MP dose during maintenance therapy administered to two patients with the ITPA deficiency was lower than that given to the other patients. Measuring ITPA activity is important for ensuring the safety of maintenance therapy for Asians with ALL because thiopurine S-methyl transferase mutations are rare in the Asian population.

Thiopurine S-methyltransferase (TPMT) polymorphisms in children with acute lymphoblastic leukemia, and the need for reduction or cessation of 6-mercaptopurine doses during maintenance therapy: the Polish multicenter analysis

BACKGROUND

6-Mercaptopurine (6-MP) is used for the treatment of pediatric acute lymphoblastic leukemia (ALL). Mutations in the TPMT gene may influence the efficacy and safety of 6-MP treatment. This multicenter study investigated the association between TPMT genotype, 6-MP dose adjustments, and the incidence of adverse effects in patients.

PROCEDURE

A total of 203 ALL children were genotyped using PCR/allele-specific amplification and PCR/RFLP. The control group consisted of 394 healthy volunteers.

RESULTS

The TPMT*3A variant allele was found in 16 patients (15 TPMT*1/*3A, 1 TPMT*3A/*3A) and the TPMT*3C (A719G) allele in 1 patient. No TPMT*2 (G238C) or TPMT*3B (G460A) alleles were detected in the study group. TPMT*3A, TPMT*1 (wild-type), and TPMT*3C alleles were detected at frequencies of 3.94%, 95.81%, and 0.25%, respectively. The genotype and allele distributions were similar in the ALL and control groups. The 6-MP dose was reduced more frequently in patients with TPMT*3A and TPMT*3C alleles, compared with wild-type alleles (P = 0.042). Reductions because of leucopenia with respiratory tract infection, or because of leucopenia, anemia and/or thrombocytopenia were four (P = 0.007) and five (P = 0.03) times more common, respectively. The groups differed with regard to the rates of 6-MP dose reduction (P = 0.028). 6-MP was discontinued more often in patients with TPMT*3A and TPMT*3C alleles (14-fold) as a result of leucopenia, anemia, and/or thrombocytopenia (P = 0.004).

CONCLUSIONS

The results indicate that TPMT genotype influences the safety and efficacy of ALL treatment and genotype information may therefore be useful for optimizing 6-MP therapy.