PADI4 and rheumatoid arthritis: The combination of the homozygous PADI4 haplotype and smoking increased the risk in patients with RA (for erosive RA (OR 4.22, 95% CI 1.95 to 9.17); for non-erosive RA (OR 8.59, 95% CI 3.27 to 22.56)) (Supplementary table S2 in Additional file 1).