The IgA ACPA repertoire has been studied to a lesser extent than IgG ACPA, but the IgA ACPA repertoire might be of importance since mucosal inflammation has been hypothesized to play a role in the initiation of RA [19] and similar to IgG ACPA, IgA ACPA emerge before the onset of clinical RA [20]. Here, PRTN3 is linked to rheumatoid arthritis.