Peptidyl-arginine-deiminase (PAD) plays a crucial role in RA by facilitatingcitrullination, which converts protein arginine residues to citrulline.This citrullination process produces autoantibodies against citrullinatedproteins called anticitrullinated protein antibodies (ACPA).42 ACPA serves as a diagnostic marker for RA andis believed to contribute to disease development and progression bytriggering immune responses and promoting joint inflammation. This evidence concerns the gene PADI4 and rheumatoid arthritis.