OBJECTIVE: To replicate the association reported in Japanese individuals of functional SLC22A4 and RUNX1 polymorphisms with rheumatoid arthritis (RA), and to test the possible role in this trait of a functional variant of the SUMO4 gene that was shown to be associated with another related autoimmune disease, type 1 diabetes (T1D). METHODS: Our study population consisted of 886 patients with RA and 987 healthy controls. All subjects were of Spanish Caucasian origin. We conducted a case-control association study with 6 single-nucleotide polymorphisms (SNP) spanning the SLC22A4 gene. SNP mapping in the RUNX1 gene associated with RA in a Japanese population and a SUMO4 polymorphism associated with T1D were also studied. RESULTS: No statistically significant differences between patients with RA and healthy controls were observed when comparing the distribution of the genotypes or alleles of any of the SLC22A4 polymorphisms tested. Similarly, no evidence of association between RA and the SLC22A4 haplotype previously reported to be associated in a Japanese population was found. With regard to the RUNX1 and SUMO4 SNP, we did not observe statistically significant differences in the distribution of genotypes or alleles between patients with RA and healthy controls. CONCLUSION: These results suggest that the SLC22A4, RUNX1, and SUMO4 polymorphisms analyzed do not confer a relevant role in susceptibility to RA in the Spanish population.