Further insight about a relationship between Gd-IgA1 and nephritis has come from other observations: (1) Gd-IgA1 (57) and IgA–IgG circulating immune complexes (58) are in sera of patients with HSP with nephritis but not in sera of patients with HSP without nephritis and (2) patients with IgA1 myeloma have high circulating levels of IgA1, but only those with aberrantly glycosylated IgA1 develop immune complex glomerulonephritis (59, 60). This evidence concerns the gene CD79A and hereditary spastic paraplegia.