Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease causing joint damage and significant functional impairment. Methotrexate (MTX) remains the mainstay for the treatment of RA. MTX inhibits several enzymes of the folate and nucleotide pathways. Thymidylate synthase (TYMS) is an important enzyme in the de novo pyrimidine pathway responsible for DNA replication. The two common gene polymorphisms analyzed in TYMS are 28-bp tandem repeat polymorphism and a 6-bp insertion/deletion polymorphism. The present study was carried out to find the role of these TYMS gene polymorphisms with clinical phenotype, treatment response, and MTX adverse events in 254 patients with RA of south Indian Tamil ethnicity. TYMS gene polymorphisms were analyzed by PCR. The allele frequencies of TYMS gene polymorphisms did not differ between good and non-responders. However, the TYMS 28-bp tandem repeat 3R allele was higher in non-responders than in patients undergoing remission [64 vs 51.11%, p = 0.06, OR 0.58, 95% CI (0.34-1.00)]. The TYMS 6-bp deletion allele was higher in non-responders than good responders [78.20 vs 64.92%, p = 0.06, OR 0.51 95% CI (0.27-0.98)]. TYMS 3R allele and TYMS 6-bp deletion allele may favor non-response to MTX in south Indian Tamils. TYMS gene polymorphisms did not influence MTX adverse events.
Keywords: Methotrexate; Rheumatoid arthritis; South Indian; Thymidylate synthase; Treatment response.