Abnormal glycosylation of serum IgG in patients with IgA nephropathy

Background We postulated that IgA nephropathy (IgAN) involved alterations of serum IgG. The present study was undertaken to elucidate changes in serum IgG oligosaccharide structure analysis and to assess the diagnostic usefulness of this analysis in IgAN. Methods The subjects were 28 children who were definitively diagnosed as having IgAN on the basis of renal biopsy and who had not received treatment for this disease; 27 healthy children; 15 untreated adults definitely diagnosed as having IgAN; 5 patients with other nephropathies; and 61 healthy adults. Oligosaccharide analyses of IgG were performed by reverse-phase high-performance liquid chromatography (HPLC) developed by Takahashi and colleagues. Results In both the children and the adults, the peak area ratio of isomers with two different galactosyl-N-acetylglucosamine (Gal-GlcNAc) binding sites was significantly lower in the presence of IgAN than in the healthy subjects (P < 0.05 in children and P < 0.001 in adults). The ratio of Gal-free oligosaccharides to Gal-positive oligosaccharides did not differ according to the presence or absence of IgAN in children or in adults. Conclusions The analysis of the oligosaccharide structure of serum IgG seems to be useful in diagnosing IgAN.