To ensure that we did not introduce additional bias into our data, we compared the demographic data (age, gender, disease duration and radiographic damage) of ACPA IgG-positive RA patients who had ACPA IgM ≥ 100 AU/ml with those who had ACPA IgM < 100 AU/ml and observed no differences. This evidence concerns the gene PRTN3 and rheumatoid arthritis.