PRTN3 and rheumatoid arthritis: The presence of these autoantibodies can be seen in 50% of early RA patients and in up to 80% of patients with established RA.1 This is explained by the fact that seronegative disease is more transient: Many RF‐ and ACPA‐negative patients do not develop a chronic progressive disease, and therefore, cohorts following patients over a long period of time retain mostly seropositive patients.