PRTN3 and rheumatoid arthritis: Previous studies in patients with ACPA-positive arthralgia showed a higher risk of RA progression in patients with high levels of anti-CCP [30], but in the study of Verpoort et al. [26], although a trend toward high levels of anti-CCP was observed in patients with CCP-positive RA compared to CCP-positive undifferentiated arthritis for all isotypes, no significant differences were observed when negative samples were excluded.