PRTN3 and rheumatoid arthritis: In the first study addressing this issue it was found that the occurrence of IgA-class antibodies was associated with smoking, and IgA-ACPA positive early RA patients had a more severe disease course over 3 years compared with IgA-ACPA negative cases, portending pathogenetic implications and a potential prognostic value of IgA-ACPA [26].