For example, in studies of early arthritis cohorts, most patients who only fulfil the 1987 classification criteria for RA (characterised by the hallmarks of established RA such as radiological damage and nodulosis), and not the 2010 criteria (characterised by raised inflammatory markers and swollen/tender joint counts), are negative for RF and ACPA.8, 9, 19 Knowledge of anti-CarP antibody status in these patients, therefore, may be especially useful. Here, PRTN3 is linked to rheumatoid arthritis.