The link between RA and PD is also suggested by the fact that inflamed human periodontal tissue is an extrasynovial source of malondialdehyde-acetaldehyde (MAA)-modified proteins compared to healthy gingival tissue, and at the same time, anti-MAA antibody isotype responses are associated with ACPA in RA patients [87,88]. Here, PRTN3 is linked to rheumatoid arthritis.