For instance, anti-citrullinated peptide antibodies (ACPA), which are associated with a worse outcome and a more erosive disease course in RA can be identified in 4.4–27.3% of patients with SLE [9, 10], and their prevalence is even higher in patients with x-ray-detected erosive arthritis, reaching 50% [11, 12]. This evidence concerns the gene PRTN3 and rheumatoid arthritis.