This study aimed to evaluate the salivary levels human leukocyte antigen-DR4 (HLA-DR4), matrix metalloproteinase-8 (MMP-8), and anti-citrullinated protein antibody (ACPA), and to assess their diagnostic potential using ROC curve analysis in periodontitis patients with and without rheumatoid arthritis. The gene discussed is PRTN3; the disease is periodontitis.