PRTN3 and rheumatoid arthritis: We found anti-CII in 6.6% of the patients with RA; a figure close to the 8.8% we reported previously.11 Although anti-CII-positive RA represent a small group as compared with ACPA, the anti-CII-associated phenotype is so profound that also the small group of patients single positive for anti-CII (2.2%; 20/773) show a strong and statistically highly significant phenotype as compared with antibody-negative patients (table 1).