Are Thymidylate synthase and Methylene tetrahydrofolate reductase genes linked with methotrexate response (efficacy, toxicity) in Indian (Asian) rheumatoid arthritis patients?

Methotrexate (MTX) is among the best-tolerated disease-modifying antirheumatic drugs for the treatment of rheumatoid arthritis (RA); major drawbacks of MTX therapy are the large interpatient variability in clinical response and the unpredictable appearance of a large spectrum of side effects. Several studies have demonstrated gene polymorphism that may regulate intracellular methotrexate metabolic pathway enzymes linked to drug efficacy and safety, but the evidence available is not yet conclusive. We decided to run a pilot study to determine the incidence of Methylene tetrahydrofolate (MTHFR; C677T, A1298C) and Thymidylate synthase (TS; 5' UTR repeat, 3' UTR deletion) gene polymorphism in rheumatoid arthritis patients in our community (Indian Asian) and further explore its association with MTX response (efficacy, toxicity). Thirty-four naïve RA patients on supervised MTX therapy and 139 healthy controls were genotyped for A1298C and C677T polymorphism of the MTHFR gene and 5' UTR repeat and 3' UTR deletion polymorphism of the TYMS gene by polymerase chain reaction-restriction fragment length polymorphism. Association, if any, between gene polymorphism and MTX response in RA patients was analyzed. The MTHFR A1298C 'C' allele incidence among RA patients (46%) was significantly higher (chi2 = 4.24, P < 0.05, OR = 1.68). None of the other allele tested showed any association. Although a small sample study, our findings do not suggest a significant association of MTHFR/TS allele/genotype with MTX response in our ethnically distinct Indian (Asian) RA patients.