PRTN3 and rheumatoid arthritis: The absent correlation between levels of autoantibodies and disease activity is not unusual in diverse rheumatic diseases; levels of rheumatoid factor (RF) and autoantibodies against citrullinated proteins (ACPA) in rheumatoid arthritis, and antiphospholipid antibody titers in antiphospholipid syndrome do not correlate with disease activity, although RF/ACPA and antiphospholipid promote joint destruction and thrombus formation, respectively [25].