TYMS and rheumatoid arthritis: This study concluded that TYMS polymorphisms seem to be important to predict clinical response to MTX in RA patients; TYMS genotypes and haplotypes harboring 6bp− allele were associated with non-response to MTX; TYMS haplotypes harboring simultaneously 3R and 6bp− alleles seem to be predictors of non-response to MTX; and, to elucidate the role of TYMS on MTX therapeutic outcome full haplotypic information should be exploited.