PADI4 and rheumatoid arthritis: The autoantibodies associated with RA predominantly include rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), anti-modified citrullinated vimentin antibody, anti-carbamylated protein antibody, anti-peptidyl arginine deiminase 4 (PAD-4) antibody, anti-glucose-6-phosphate isomerase (GPI) antibody and so on [8].