PADI4 and rheumatoid arthritis: In light of recent observations of the presence of inflammation-associated citrullination, presence of PAD-2 and PAD-4 in gingival tissues [28], [48] as well as PPAD in serum [49] now provides good evidence for another important extra-articular source for citrullination and anti-citrullinated protein antibody production to occur years in advance of the development of the clinical signs and symptoms of RA.