Gene Variant Common in Individuals of African Ancestry May Lead to Reduced Metabolism of the Thiopurine Class of Drugs

Mayo Clinic researchers found that a gene variant, the TPMT∗8 allele, is associated with reduced metabolism of the thiopurine class of drugs. TPMT∗8 is relatively common in individuals of African or African American descent. A novel study 新しいタブ／ウィンドウで開く in The Journal of Molecular Diagnostics 新しいタブ／ウィンドウで開く, published by Elsevier, details the researchers' goal to provide pharmacogenomic testing that can be used clinically to predict drug response that is beneficial to all patients, regardless of their ancestral background.

Thiopurines are a class of drugs that can be used to treat a variety of medical conditions including leukemia, inflammatory bowel disease, and autoimmune disorders. TPMT is an enzyme important in metabolizing thiopurine medications that limits the levels of active metabolite, which contributes to toxicity.

First author Rosalie M. Sterner, MD, PhD, Department of Laboratory Medicine and Pathology, Mayo Clinic in Rochester, notes, "Variants in the TPMT gene can result in decreased enzyme activity. Thus, to prevent thiopurine adverse reactions, individuals are tested to see if they have genetic variants prior to initiation of treatment, so dosing can be adjusted according to enzyme activity. Currently, guidelines do not recommend testing for the TPMT∗8 variant, which is a variant common among individuals of African or African American ancestry (2.3% minor allele frequency) as its function has been considered uncertain."

Researchers combined data from two assays: one to measure TPMT activity and the other that performs genotyping. They compared the TPMT activity of individuals who carry one copy of the TPMT∗8 allele (and one normal copy) to individuals who are considered intermediate metabolizers (they have one normal copy of TPMT and one no function copy of TPMT). They found that individuals who carry TPMT∗8 metabolized the chemotherapeutic 6-mercaptopurine to 6-methylmercapture purine slower than normal metabolizers (two normal copies of TPMT), but faster than the intermediate metabolizers.

Co-lead investigator Ann M. Moyer, MD, PhD, Department of Laboratory Medicine and Pathology, Mayo Clinic in Rochester, explains, "This is important because a competing reaction converts 6-mercaptopurine to the active metabolites that are responsible for toxicity, and reduced TPMT activity is associated with thiopurine toxicity. In addition, we found that the TPMT activity differed with respect to three substrates (6-MP, 6-MPR, and 6-TGR)."

Co-lead investigator John L. Black, MD, Department of Laboratory Medicine and Pathology, Mayo Clinic in Rochester, notes, "Genotyping will only detect the alleles that are targeted by a test. Some laboratories, including ours, are moving to sequencing pharmacogenes by next-generation sequencing (NGS), which allows the detection of all alleles. This sometimes yields results that can be useful when the rare allele has a known function. Equally important, this approach is superior in providing service to individuals of all ancestries because alleles, including rare alleles, often cluster within ancestral groups. NGS sequencing reduces the ethnocentric approach driven by the fact that most tests have been designed for only the most commonly studied ancestral groups.”

This study showing that TPMT∗8 is a reduced function allele could result in recognition of reduced function alleles and more accurate and granular phenotype prediction. However, this would require further study to understand the clinical significance (thiopurine dose tolerated) of reduced function alleles, incorporation into clinical dosing guidelines, and inclusion in allele selection recommendations. These findings have the potential to help shape clinical practice.

Dr. Sterner concludes, "The commonly tested TPMT variants result in a protein with no activity, so as a next step, it will be important to determine whether a dose reduction is warranted in individuals with reduced function alleles, alone or in combination with other variants."

Notes for editors

The article is “Genotype and Phenotype Correlation of the TPMT∗8 Allele in Thiopurine Metabolism,” by Rosalie M. Sterner, MD, PhD, Patricia L. Hall, PhD, Dietrich Matern, MD, PhD, John L. Black, MD, and Ann M. Moyer, MD, PhD (https://doi.org/10.1016/j.jmoldx.2024.07.005 新しいタブ／ウィンドウで開く). The article appears in The Journal of Molecular Diagnostics, volume 26, issue 11 (November 2024), published by Elsevier 新しいタブ／ウィンドウで開く.

The article is openly available for 30 days at https://www.jmdjournal.org/article/S1525-1578(24)00183-1/fulltext 新しいタブ／ウィンドウで開く.

Full text of this article and additional information are also available to credentialed journalists upon request; contact Eileen Leahy at +1 732 406 1313 or [email protected] 新しいタブ／ウィンドウで開く. Journalists wishing to interview the study authors should contact Susanne Ferguson, Mayo Clinic in Rochester, at [email protected] 新しいタブ／ウィンドウで開く.

About The Journal of Molecular Diagnostics

The Journal of Molecular Diagnostics 新しいタブ／ウィンドウで開く, the official publication of the Association for Molecular Pathology, co-owned by the American Society for Investigative Pathology, and published by Elsevier, seeks to publish high quality original papers on scientific advances in the translation and validation of molecular discoveries in medicine into the clinical diagnostic setting, and the description and application of technological advances in the field of molecular diagnostic medicine. The editors welcome review articles that contain: novel discoveries or clinicopathologic correlations, including studies in oncology, infectious diseases, inherited diseases, predisposition to disease, or the description of polymorphisms linked to disease states or normal variations; the application of diagnostic methodologies in clinical trials; or the development of new or improved molecular methods for diagnosis or monitoring of disease or disease predisposition. https://www.jmdjournal.org/ 新しいタブ／ウィンドウで開く

エルゼビアについて エルゼビアは、科学情報と分析を牽引するグローバル企業として、研究者や医療従事者が社会の利益のために科学を進歩させ、医療成果を向上させることを支援しています。我々は信頼できるエビデンスベースのコンテンツと高度なAI対応デジタルテクノロジーに基づくソリューションにより、インサイトと重要な意思決定を促進することでこれを実現しています。

エルゼビアは、140 年以上にわたり研究および医療コミュニティの活動を支援してきました。全世界で 2,500 人以上の技術者を含む 9,500 人の従業員がおり、重要な職務における研究者や、図書館員、アカデミックリーダー、資金提供者、政府機関、R&D 関連企業、医師、看護師、将来の医療従事者や教育者を支援することに従事してきました。2,900 誌以上の科学ジャーナルと代表的な参考文献には、Cell Press、The Lancet、Gray's Anatomy など、各分野の主要なタイトルを含みます。 エルゼビア・ファウンデーション 新しいタブ／ウィンドウで開くと共に、開発途上国および世界中の科学、研究、医療分野におけるインクルージョン＆ダイバーシティ 新しいタブ／ウィンドウで開くを推進するため、支援コミュニティと連携して活動しています。 エルゼビアは、プロフェッショナルおよびビジネス顧客向けの情報に基づく分析および意思決定ツールのグローバルプロバイダーである RELX 新しいタブ／ウィンドウで開くグループの一部です。業務内容やデジタルソリューション、コンテンツ詳細については、 www.elsevier.com/ja-jpをご参照ください。