PRTN3 and rheumatoid arthritis: In our analysis there was a statistically significant gene-environment interaction (additive P value = 0.0034 in current smokers and P value = 0.016 in ever smokers) between rs6933349 and smoking in the risk of developing ACPA-positive RA, with an attributable proportion due to the interaction (AP) value of 0.315 (95% CI 0.104 to 0.526) in current smokers and 0.216 (95% CI 0.040 to 0.392) in ever smokers (Table 1).