In summary, this is the first study to present the concentrations and cartilage-degrading potential of PR3 (while confirming elevated levels of HLE and MPO, both markers of neutrophil recruitment and degranulation) in the synovial fluid of JIA patients, thus highlighting the previously overlooked contribution of PR3 to the pathophysiology of JIA. The gene discussed is PRTN3; the disease is juvenile idiopathic arthritis.