Background Therapeutic outcome of rheumatoid arthritis (RA) patients treated with methotrexate (MTX) could be conditioned by thymidylate synthase (TS) levels, which may be altered by genetic polymorphisms in TS gene (TYMS) [1,2].
Objectives The aim of this study was to elucidate the clinical relevance of three TYMS polymorphisms, using genotype and haplotype-based approaches, in MTX therapeutic outcome (regarding both response and overall toxicity) in Portuguese RA patients.
Methods This study included 233 Caucasian RA patients treated with MTX. Clinicopathological data were collected, outcomes were defined and patients were genotyped using polymerase chain reaction-restriction fragment length polymorphism or sequencing technology for the following TYMS polymorphisms: 1)28 base pairs (bp) variable number tandem repeat (rs34743033); 2)single nucleotide polymorphism (SNP) C>G (rs2853542); and 3)6bp sequence deletion (1494del6, rs34489327). For statistical analysis, chi-square and binary logistic regression analyses were performed. Haplotype analyses were used to better understand the contribution of TYMS in MTX therapeutic outcome.
Results Considering TYMS genotypes, 3R homozygotes (p=0.005;OR=2.34), 3RC3RG genotype (p=0.016;OR=3.52) and 6bp- carriers (p=0.011;OR=1.96) were associated with non-response to MTX, when compared to 2R carriers, 2R3RG and 6bp+ homozygotes, respectively. Multivariate analyses confirmed the increased risk for non-response to MTX in 6bp- carriers (p=0.020;OR=2.40). TYMS polymorphisms were in linkage disequilibrium in our population (p<0.00001) and alleles 2R and 6bp+ were the most frequent and linked ones (D'=0.67). The haplotype analysis revealed that 3R6bp- (p=0.001;OR=2.54), 3RC6bp+ (p=0.041;OR=1.79), 3RC6bp- (p=0.013;OR=2.80) and 3RG6bp- (p=0.009;OR=2.39) were associated with non-response to MTX when compared to 2R6bp+ haplotype. Multivariate analysis demonstrated that 3R6bp- (p=0.012;OR=2.68), 3RC6bp- (p=0.048;OR=2.89) and 3RG6bp- (p=0.043;OR=2.60) were associated with non-response to MTX when compared to 2R6bp+. Regarding MTX-related toxicity, no statistically significant differences were observed in relation to TYMS genotypes and haplotypes.
Conclusions TYMS polymorphisms seem to be important to help predicting clinical response to MTX in RA patients and not important in predicting MTX-related toxicity. Moreover, the effect of TYMS 1494del6 polymorphism in clinical response is possibly stronger. Despite the potential of these findings, translation into clinical practice needed larger studies to provide positive confirmation.
Lima A, Azevedo R, Sousa H, Seabra V, Medeiros R (2013) Current approaches for TYMS polymorphisms and their importance in molecular epidemiology and pharmacogenetics. Pharmacogenomics 14 (11):1337-1351.
Kumagai K, Hiyama K, Oyama T, Maeda H, Kohno N. Polymorphisms in the thymidylate synthase and methylenetetrahydrofolate reductase genes and sensitivity to the low-dose methotrexate therapy in patients with rheumatoid arthritis. Int J Mol Med. 2003 May;11(5):593-600.
Acknowledgements The authors wish to acknowledge to Fundação para a Ciência e Tecnologia (FCT) for the Doctoral Grant (SFRH/BD/64441/2009) for Aurea Lima and also to the nursing service of Rheumatology Day Hospital of São João Hospital Center and the clinicians from the Rheumatology Department of São João Hospital Center.
Disclosure of Interest : None declared