Consistent with previous reports16, the frequencies of terminally sialylated glycoforms, G1FS1 (peak 1), G2FS1 (peak 2), and G2FS2 (peak 4) were equivalently reduced in both IgG1 ACPA and total IgG1 from RA patients compared with total IgG1 from healthy donors; no difference was found between ACPA and total IgG1 from RA patients (Fig. 1d). The gene discussed is PRTN3; the disease is rheumatoid arthritis.