SLC19A1 and rheumatoid arthritis: A recent systematic review reported associations between MTX response in RA patients and single-nucleotide polymorphisms (SNPs) in the MTHFR gene 1298A>C (rs1801131), ATIC gene 347C>G (rs2372536), RFC-1 gene 80G>A (rs1051266), SLC19A1 A>G (rs2838956) and SLC19A1 gene G>A (rs7499) [200].