HC; healthy controls, RA; rheumatoid arthritis, ACPA; anti-citrullinated protein antibodies, anti-CarP antibody ; anti-carbamylated protein antibody, FCS; fetal calf serum, CaFCS; carbamylated fetal calf serum, AU/ml; arbitrary units per millilitre. The gene discussed is PRTN3; the disease is rheumatoid arthritis.