Prevalence of thiopurine S-methyltransferase gene polymorphisms in patients with inflammatory bowel disease from the island of Crete, Greece

The Role of Pharmacogenetics in the Therapeutic Response to Thiopurines in the Treatment of Inflammatory Bowel Disease: A Systematic Review

This study focuses on the use of thiopurines for treating inflammatory bowel diseases (IBD). These drugs undergo enzymatic changes within the body, resulting in active and inactive metabolites that influence their therapeutic effects. The research examines the role of genetic polymorphisms in the enzyme thiopurine S-methyltransferase (TPMT) in predicting the therapeutic response and adverse effects of thiopurine treatment. The TPMT genotype variations impact the individual responses to thiopurines. Patients with reduced TPMT activity are more susceptible to adverse reactions (AEs), such leukopenia, hepatotoxicity, pancreatitis, and nausea, which are common adverse effects of thiopurine therapy. The therapeutic monitoring of the metabolites 6-thioguanine nucleotides (6-TGN) and 6-methyl mercaptopurine (6-MMP) is proposed to optimize treatment and minimize AEs. Patients with higher 6-TGN levels tend to have better clinical responses, while elevated 6-MMP levels are linked to hepatotoxicity. Genotyping for TPMT before or during treatment initiation is suggested to tailor dosing strategies and enhance treatment efficacy while reducing the risk of myelosuppression. In conclusion, this study highlights the importance of considering genetic variations and metabolite levels in optimizing thiopurine therapy for IBD patients, focusing on balance therapeutic efficacy with the prevention of adverse effects and contributing to personalized treatment and better patient outcomes.

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.

Systematic review with meta-analysis: risk factors for thiopurine-induced leukopenia in IBD

BACKGROUND

Thiopurine-induced leukopenia, a frequently observed and potentially life-threatening adverse event, complicates the clinical management of IBD patients.

AIM

To assess risk factors for thiopurine-induced leukopenia in IBD.

METHODS

MEDLINE, EMBASE, BIOSIS and Cochrane library were searched for studies reporting at least one risk factor for thiopurine-induced leukopenia. Pooled odds ratio (OR) was calculated for each potential risk factor using a random effects model. Studies that were not eligible for meta-analysis were described qualitatively.

RESULTS

Seventy articles were included, 34 (11 229 patients) were included in meta-analyses. A significantly higher thiopurine-induced leukopenia risk was found for TPMT (OR 3.9, 95% [CI] 2.5-6.1) and for NUDT15 R139C (OR 6.9, 95% CI 5.2-9.1), G52A (OR 3.2, 95% CI 1.3-7.9) and 36_37ins/delGGAGTC variant carriers (OR 5.6, 95% CI 2.8-11.4). A potential association between high 6-thioguanine nucleotides (6-TGN) or 6-methylmercaptopurine (6-MMP) levels and leukopenia was observed, since most studies reported higher metabolite levels in leukopenic patients (6-TGN: 204-308 (Lennard method) and 397 (Dervieux method), 6-MMP: 4020-10 450 pmol/8 x 10⁸ RBC) compared to controls (6-TGN: 170-212 (Lennard method) and 269 (Dervieux method), 6-MMP: 1025-4550 pmol/8 x 10⁸ RBC).

CONCLUSIONS

TPMT and NUDT15 variants predict thiopurine-induced leukopenia. High 6-TGN and 6-MMP levels might induce leukopenia, although exact cut-off values remain unclear. Potential preventive measures to reduce the risk of thiopurine-induced leukopenia include pre-treatment TPMT and NUDT15 genotyping. Routine thiopurine metabolite measurement might be efficient, yet cut-off levels must be validated in advance.