Although several biomarkers routinely used in RA management, such as anti-citrullinated protein autoantibodies (ACPA) and rheumatoid factor (RF) tests, have greatly contributed to improving the early diagnosis of RA [57], there is a high demand for novel biomarkers to further improve not only the diagnosis but also the stratification of patients and even the prediction of response to a specific therapy. Here, PRTN3 is linked to rheumatoid arthritis.