PADI4 and rheumatoid arthritis: Single-nucleotide polymorphisms in the gene for PAD4, PADI4, are consistently associated with RA [7, 8] in Asian population and possibly also in Caucasian populations [9], further strengthening the notion that granulocyte-derived PAD4 may be a key player in the citrullination of proteins in the synovial fluid, which subsequently acts as autoantigens to trigger an immune response resulting in anti-citrulline-peptide antibodies [6].