To determine whether the observed association between IgG Fc galactosylation and bone volume is due to a direct effect of IgG Fc galactosylation or simply the fact that galactose is needed for the attachment of sialic acid to the IgG glycan, we enzymatically galactosylated and sialylated two human monoclonal ACPA (clones 109 and C7) (Supplementary Fig. 6) that have been generated from B cells from the joints of rheumatoid arthritis patients30. Here, PRTN3 is linked to rheumatoid arthritis.