ABCB1 and rheumatoid arthritis: Significant associations were not observed between the MTHFR (677C > T (rs1801133) and 1298A > C (rs1801131)), ATIC 347C > G (rs2372536), MTR 2756A > G (rs1805087), MTRR 66A > G (rs1801394), ABCB1 3435C > T (rs1045642), and RFC-1 80G > A (rs1051266, when all the patients were included) and the toxicity of MTX in RA patients.