In RA pathogenesis, citrullinated proteins are generated by the activity of specific enzymes, named peptidyl-arginine-deiminases (PAD) type IV, that catalyze the modifications of peptidyl-arginine to peptidyl-citrulline on several self-proteins, including α-enolase, keratin, fibrinogen, fibronectin, collagen, and vimentin. This evidence concerns the gene FN1 and rheumatoid arthritis.