The fact that we found elevated anti-Rgp IgG levels in ACPA-positive at-risk individuals compared with ACPA-negative controls, and that levels remained stable over time, did not predict the onset of arthritis, or associate with factors known to predict arthritis onset in this Risk-RA cohort (eg, high anti-CCP2 IgG levels, RF and HLA-DRB1 SE11), suggest that anti-Rgp IgG could be related to the autoimmune ACPA-response per se rather than to arthritis. Here, PRTN3 is linked to arthritic joint disease.