The best-known and -studied autoantibodies, which play a major role in the development of RA, are rheumatoid factor (RF), but also anti-carbamylated proteins, anti-citrullinated protein antibodies (ACPA), anti-PAD-4, anti-GPI and anti-cyclic citrullinated peptide (anti-CCP) antibodies [191,192]. The gene discussed is GPI; the disease is rheumatoid arthritis.