IGHA1 and rheumatoid arthritis: Wada et al. (2010) demonstrated the reduced GalNAc glycosylation in the IgA1 hinge region in the circulatory system of RA patients by mass spectrometry. Kratz et al. (2010) found that there were changes in Sia and Gal modifications on both IgG and IgA in the joint effusion of early RA patients.