PRTN3 and rheumatoid arthritis: The frequency of autoantibodies was lower than expected [35–37], but still comparable with other early arthritis cohorts from similar geographical areas [38], including the Etude et Suivi des POlyarthrites Indifférenciées Récentes (ESPOIR) cohort, in which 46–49 % of the patients fulfilling the RA classification criteria at inclusion are reported as ACPA-positive [39–41].