PRTN3 and rheumatoid arthritis: The presence of anti-citrullinated peptide antibodies (ACPA) is associated with RA with higher specificity than rheumatoid factor; thus, ACPA is thought to play some role in the pathogenesis of RA, especially as SE alleles are strongly associated with ACPA-positive RA but only relatively weakly with ACPA-negative RA [5].