We also did not find any statistically significant interaction between the homozygous PADI4 haplotype and smoking in anti-CCP-positive RA (AP 0.23, 95% CI -0.37 to 0.83) and anti-CCP-negative RA (AP 0.18, 95% CI -0.72 to 1.08). This evidence concerns the gene PADI4 and rheumatoid arthritis.