Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Methylene tetrahydrofolate reductase gene polymorphisms and their association with methotrexate toxicity: a meta-analysis Kalliopi P. Spyridopoulou a , Niki L. Dimou b , Stavros J. Hamodrakas a and Pantelis G. Bagos b Objective A systematic review and a meta-analysis were conducted, to investigate the possible association of methylene tetrahydrofolate reductase (MTHFR) gene polymorphisms with adverse effects related to methotrexate (MTX). Methods A systematic literature search in PubMed retrieved a total of 44 studies (42 unique articles). Two polymorphisms were included in the meta-analysis: C677T and A1298C. Random effect models were used in the analysis. Odds ratios along with their 95% confidence intervals were computed to compare the distribution of alleles and genotypes between cases and controls. Results The analysis highlighted a significant association of C677T polymorphism with overall MTX toxicity, hepatotoxicity, hematological toxicity, and neurotoxicity. It also revealed an association with MTX toxicity in patients with rheumatoid arthritis. In contrast, a protective effect of C677T MTHFR polymorphism on acute graft-versus-host disease and on patients treated with hematopoietic cell transplantation was found. As for the A1298C polymorphism, a statistically significant association with overall MTX toxicity and a protective role of the polymorphism in rheumatoid arthritis patients was detected. Conclusion These results indicate the association of MTHFR polymorphisms with MTX toxicity. However, further studies are needed to reveal the underlying biological mechanism of the association. Pharmacogenetics and Genomics 00:000–000 c 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins. Pharmacogenetics and Genomics 2011, 00:000–000 Keywords: gene polymorphisms, meta-analysis, methotrexate toxicity, methylene tetrahydrofolate reductase a Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, Athens and b Department of Computer Science and Biomedical Informatics, University of Central Greece, Papasiopoulou, Lamia, Greece Correspondence to Dr Pantelis G. Bagos, Department of Computer Science and Biomedical Informatics, University of Central Greece, Papasiopoulou 2-4, Lamia 35100, Greece Tel: + 30 223 106 6914; fax: + 30 223 106 6915 e-mail: pbagos@ucg.gr Received 20 November 2011 Accepted 7 October 2011 Introduction Methotrexate (MTX) is a widely used drug in the treatment of a variety of diseases such as cancer, acute lymphoblastic leukemia or lymphoma, hematopoietic cell transplantation, rheumatoid arthritis, psoriasis, inflamma- tory bowel disease, and other diseases [1,2]. As a structural analogue of folic acid, MTX reversibly inhibits dihydrofolate reductase, an enzyme that participates in the tetrahydrofolate synthesis [3–5]. MTX is also known to inhibit other enzymes in the folic acid cycle, such as thymidylate synthase and methylene tetrahydrofolate reductase (MTHFR) [6,7]. As an inhibitor of DNA and protein synthesis, MTX interferes with and inhibits the growth of normal cells and tissues besides the target abnormal cells. It can, therefore, cause a significant number of side effects that may lead to therapy discontinuation. The most common side effects include oral mucositis, nausea, diarrhoea, and alopecia. Furthermore, it may also cause serious toxicities in liver, bone marrow, pulmonary, and the central nervous system [8,9]. A special kind of toxicity of MTX in patients treated with hematopoietic cell transplantation is acute graft-versus-host disease (GVHD). MTHFR catalyses the conversion of 5,10-methylene- tetrahydrofolate to 5-methyltetrahydrofolate in folic acid cycle, and thus, it plays an essential role in nucleotide biosynthesis. In contrast, 5-methyltetrahydrofolate acts as a methyl donor for the remethylation of homocysteine to methionine. There are two common single-nucleotide polymorphisms (SNPs) of MTHFR: C677T and A1298C. The C677T polymorphism changes alanine to valine at the 222 position of the amino acid sequence. The enzyme activity of the TT homozygote is decreased compared with that of the CC homozygote [10,11]. The A1298C polymorphism is responsible for the substitution of glutamate by alanine at the 429 position of the protein [12,13]. This polymorphism has been associated with a reduced MTHFR activity in vitro. The reduced enzyme activity leads to high blood homocysteine levels and this disorder is connected to coronary and peripheral artery diseases [14]. Original article 1 1744-6872 c 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/FPC.0b013e32834ded2a