PRTN3 and rheumatoid arthritis: These data which indicate that HLA-SE is a major factor in determining whether an ACPA-positive individual will develop RA, are in accordance with the recent study of ACPA reactivities in twins with ACPA without disease and twins with ACPA and RA, which showed that twins with ACPA and RA were more frequently HLA-SE positive compared with twins with ACPA without RA [11].