The keywords used to find relevant articles included RA and PD, RA and periodontal infection, RA and intestinal microbes, Citrullination and Actinomycetemcomitans, Periodontitis and RA and Citrullination, Pre-RA and ACPA+, Cyclic citrullinated peptide, Antibodies and development of RA, Precede the symptoms of RA and anti-CCP, and Anti-citrullinated protein antibodies and first-degree relatives of RA. The gene discussed is PRTN3; the disease is rheumatoid arthritis.