Studies have suggested that this association may be based on the ability of P. gingivalis to express peptidyl deiminase (PAD), an enzyme responsible for citrullination of arginine residues post-translation, which can expose individuals to citrullinated antigens and easily lead to ACPA in the appropriate immunogenetic background, possibly contributing to the pathogenesis of RA synovitis (Hitchon et al., 2010). This evidence concerns the gene PADI4 and rheumatoid arthritis.