PRTN3 and rheumatoid arthritis: Our group demonstrated that a homemade ACPA ELISA test, using chimeric fibrin/filaggrin citrullinated synthetic peptides (CFFCP) [8] had a high sensitivity and specificity for RA, and was able to detect some patients negative to commercial anti-cyclic citrullinated peptide antibodies (CCP2), the most common test used in clinical practice.