PRTN3 and rheumatoid arthritis: Svendsen et al. [32] found that IgG-EBNA1 antibody level was higher in healthy co-twins from RA twin pairs but not in RA-affected twins, and the Swedish population-based Epidemiological Investigation of RA (EIRA) cohort had lower levels of IgG-EBNA1, especially in ACPA positive RA patients [33].