When assaying the susceptibility of aberrantly glycosylated IgA1 typically observed in IgA nephropathy (IgAN) to several bacterial IgA proteases, it was found that IgA1 deficient of galactose, but not sialic acid was more resistant to bacterial proteolysis than normally glycosylated serum IgA1. This evidence concerns the gene IGHA1 and IgA glomerulonephritis.