Examines the O-linked oligosaccharide (O-glycans) structure in the glomerular immunoglobulin A1 (IgA1) in IgA nephropathy. Shift in peak distribution of IgA1 hinge glycopeptides; Number of carbohydrates composing O-glycans; Sialylation and galactosylation of IgA1 hinge glycopeptides.