ABCB1 and rheumatoid arthritis: We also updated the meta-analysis of the MTHFR (677C > T (rs1801133) and 1298A > C (rs1801131)), ABCB1 3435C > T (rs1045642), RFC-1 80G > A (rs1051266), and ATIC 347C > G (rs2372536) polymorphisms and completed the first meta-analysis on the association between MTR A2756G (rs1805087) and MTRR 66A > G (rs1801394) SNPs and the toxicity of MTX in RA patients and the MTHFR (677C > T (rs1801133) and 1298A > C (rs1801131)) and RFC-1 80G > A (rs1051266) polymorphisms were included in the homology subgroup analysis.