HLA-DRB1 and rheumatoid arthritis: In addition to these data on GSTM1, our study confirms the previously known risk factors for ACPA-positive RA, HLA-DRB1 SE alleles (OR: 3.73 95% CI: 2.83–4.92) and smoking (OR: 1.74 95% CI: 1.35–2.25) and also their combination (OR: 8.00 95% CI: 4.96–12.89).