ACPAs can be detected in approximately 67% of RA patients and serve as a useful diagnostic reference for patients with early, undifferentiated arthritis and provide an indication of likely disease progression through to RA.8,9 The ACPA-positive subset of RA has a more aggressive clinical phenotype compared to ACPA-negative subset of RA.10 It is reported that ACPA-negative RA has different genetic association patterns11 and differential responses of immune cells to citrullinated antigens12 from those of ACPA-positive subset. This evidence concerns the gene PRTN3 and rheumatoid arthritis.