PRTN3 and rheumatoid arthritis: Taken together, it was possible that rs7607479 might be involved in the development of RA via regulation of MMP-3, although it was located in the intronic region of SPAG16. Interestingly, in this study, we confirmed that MMP-3 is highly expressed in synovium tissues of ACPA-positive RA patients, and we observed significant correlation between MMP-3 expression and serum level of RF and ESR.