We did not demonstrate clinically relevant differences in US abnormalities for prediction of arthritis at the patient level between ACPA-positive and ACPA-negative patients, except for synovial thickening without the MTP joints included in the ACPA-positive patients (19% developed arthritis versus 2% who did not; note the small numbers and thus wide CIs; Additional file 1: Table S1). This evidence concerns the gene PRTN3 and arthritic joint disease.