Rheumatoid factor (RF), which consists of autoantibodies against the Fc portion of IgG, antibodies against post-translational modifications such as citrullination (anti-citrullinated peptide antibodies; ACPA) and carbamylation (anti-CarP antibodies) are the types of autoantibodies often occurring in patients with RA (Figure 2b) [192,193]. The gene discussed is PRTN3; the disease is rheumatoid arthritis.