SLC19A1 and rheumatoid arthritis: For example, RFC G80A, ATIC rs4673993, SHMT1 C1420T, SLC19A1 rs1232027 (G80A), HLA-DRB1, MTHFR rs1801133 (677C/T) and MTHFR rs1801131 (1298A/C) have been found to be associated with response to MTX treatment in patients with RA (49–54).