MTHFR 677T may be used to help identify patients with an increased likelihood of methotrexate-related adverse events (Urano et al. 2002; Evans 2002); SLC19A1 A80G has been associated with decreased methotrexate therapeutic response in individuals with rheumatoid arthritis (Dervieux et al. 2004a). Here, SLC19A1 is linked to rheumatoid arthritis.