Previously published results in our group demonstrated that Cit630-bearing peptides from α-fibrin protein, covalently coupled to the cyclic filaggrin peptide, which constitutes the CCP1 test, were the most reactive ACPA epitopes, demonstrating a comparable sensitivity and specificity for RA to the gold standard commercial CCP2 test [19]. This evidence concerns the gene PRTN3 and rheumatoid arthritis.