PADI4 and rheumatoid arthritis: Multiple factors, including genetics, environment,lifestyle, obesity, autophagy, and immune system dysregulation, contributeto disease development.2 Interestingly,although having a familial history of RA can increase a person’srisk of developing the condition 3-fold, many RA patients do not havea familial history.3 Cigarette smokingis the primary environmental factor that establishes seropositiveRA.4 Smoking induces stress on lung tissues,leading to the peptidyl arginine deiminase (PAD4)-mediated conversionof arginine to citrulline.