The spectrum of ACPA-reactive proteins identified in RA patients so far includes citrullinated filaggrin [29–31], fibrinogen [32, 33], vimentin [34–37], type II collagen [33, 38–42], α-enolase [33, 43, 44], and some viral antigens [45–47]. The gene discussed is PRTN3; the disease is rheumatoid arthritis.