PRTN3 and rheumatoid arthritis: Higher anti-CEP-1 and anti-CCP2 IgG levels were detected in the double-positive subset, and a higher number of ACPA fine specificities were recorded in CEP-1/carb-CEP-1 double-positive patients with RA, compared to CEP-1 single-positive patients; all values were significant with p values <0.0001 (Fig. 4).