PRTN3 and rheumatoid arthritis: In the initial study employing a single acetylated peptide (ac-lysine) and involving only patients with early arthritis they seemed to be less specific than ACPA, but so far this issue has not been thoroughly investigated.18 In our study, we used three peptides for AAPA detection and investigated their reactivity in patients with early RA, established RA, and an appropriate number of controls including healthy subjects and patients with various inflammatory rheumatic diseases, which were not explored in great detail in previous studies.