Some serum biomarkers like rheumatoid factor (RF) (MacGregor et al., 2000; Onuora, 2012), anti-citrullinated protein antibody (ACPA) (Padyukov et al., 2011; Stahl et al., 2012), anti-cyclic citrullinated peptide (anti-CCP) antibody (Zendman et al., 2006), C-reactive protein (CRP) (Lee et al., 2016), and erythrocyte sedimentation rate (ESR) (Orr et al., 2018) have good performance to discriminate part of typical early RA patients, but approximately 30% of patients remain seronegative using current immunoassays. Here, PRTN3 is linked to rheumatoid arthritis.