PRTN3 and rheumatoid arthritis: Although the exact cause of RA remains unknown, a set of so-named shared epitope (SE) alleles, HLA-DRB1*01 (*01:01 and *01:02), *04 (*04:01, *04:04, *04:05, and *04:08), and *10 (*10:01), have been associated with RA (2) and more specifically with anti-citrullinated protein antibody (ACPA)-positive RA (3).