ABCB1 and rheumatoid arthritis: In this study, fluorescence in situ hybridization (FISH) was used to detect the polymorphisms ABCB13435C/T, MTHFR 677C/T, and MTHFR 1298A/C in RA patients and healthy controls in order to analyze the correlation between ABCB1 3435C/T, MTHFR 677C/T, and MTHFR 1298A/C and RA susceptibility and RA subtype and to explore the possible roles of these polymorphisms in the pathogenesis of RA.