Among the 290 RA patients, 150 (51.7%) were positive for both RF and ACPA by routine diagnostics, while 21 (7.2%) and 10 (3.4%), respectively, were solely positive for either RF or ACPA (Figure 2A); 109 (37.6%) patients were negative for both antibodies and are therefore referred to as seronegative. Here, PRTN3 is linked to rheumatoid arthritis.