PRTN3 and rheumatoid arthritis: Interestingly, whereas extensive glycosylation of the variable (Fab) domain is a remarkable molecular-feature of ACPA-IgG, a recent study demonstrated that levels of ACPA Fab-glycosylation are significantly lower at disease-onset in ACPA-positive RA-patients achieving SDFR, compared to age- and gender-matched RA-patients not achieving SDFR [46].