PRTN3 and arthropathy: Indeed, compared with the totality of the patients recorded in the registry, ACPA-negative ASS patients included in this study had higher frequency of polyarthralgia (85% vs 63%, P < 0.05) and polyarthritis (41% vs 20%, P < 0.05).25 Thus, our study may actually underestimate the prognostic significance of ACPA statute for joint disease in ASS patients.