MTHFR and rheumatoid arthritis: The evidence supports an association between SNPs in the MTHFR genes c.665C>T (rs1801133, historically referred to as c.677C>T or C677T) and c.1298A>C (rs1801131) and the occurrence risk of RA [28,29,30] or the expression of inflammation markers [31,32], conditions during which inflammatory cytokines such as TNF-α, which is the direct target of TNF-α inhibitor drugs, play a fundamental role [33].