In conclusion, this study demonstrates that the MTHFR 677C/T polymorphic locus may be significantly associated with susceptibility to RA and its ACPA-positive and RF-positive subtypes in the Gansu population of China, whereas the ABCB1 3435C/T and MTHFR 1298A/C polymorphisms did not show a significant association. Here, MTHFR is linked to rheumatoid arthritis.