The anti-citrullinated peptide antibodies (ACPA), which are more frequent than the rheumatoid factor (RF), present in 70-80% of RA patients, were considered predictive markers of bone destruction since they could be detected years before the disease and be stable after, and they were associated with disease erosion and aggressiveness [3,4]. The gene discussed is PRTN3; the disease is rheumatoid arthritis.