PRTN3 and rheumatoid arthritis: ACPA positivity has been shown to be a predictive marker for the development of RA in patients with joint complaints (van Gaalen et al., 2004) and patients harbouring ACPAs experience a more aggressive disease progression than patients without ACPA (van der Helm-van Mil, Verpoort, Breedveld, Toes, & Huizinga, 2005).