Given the huge role of the innate immune system not only during the onset of RA but also during the chronification of the disease [11,19] there is also growing evidence for a role of MPO and its enzymatic products not only as a marker but as an active player during the pathogenesis of this disease [9]: The protein is secreted during degranulation and/or NETosis of stimulated neutrophils [17] and, thus, may contribute to the formation of autoantibodies during the chronification of RA [9]. The gene discussed is MPO; the disease is rheumatoid arthritis.