PRTN3 and rheumatoid arthritis: Autoimmune features, such as the presence of circulating rheumatoid factor (RF) and/or anti-citrullinated protein antibodies (ACPA), typically precede the onset of clinically manifest rheumatoid arthritis (RA) (1, 2), as defined by the 1987 American College of Rheumatology (ACR87) or the 2010 ACR/EULAR classification criteria (3, 4).