PRTN3 and rheumatoid arthritis: Out of 25.8 % of patients with S-IA who had positive RF at the time of the US scan (n = 24/93), 23 patients were subsequently diagnosed with RA (23/36, 63.3 %); similarly, a proportion of ACPA-positive S-IA patients were ulterior diagnosed with RA (18/36, 50 %).