GSTM1 and rheumatoid arthritis: In 2011, a Swedish study found that more than one copy of glutathione S-transferase M1 (GSTM1), a member of the GST family, seems to be a risk factor for autoantibody-positive RA in non-smoking females of age older than 60 years, and GSTM1 acts as a protective factor in ACPA-negative smoking men, suggesting that the copy number of the GSTM1 gene is correlated with the development and severity of RA (Lundström et al., 2011).