Diseases associated with secondary MPGN are classified as follows: (a) Autoimmune diseases: systemic lupus erythematosus, Sjögren's syndrome; (b) Infectious diseases: especially hepatitis B and C; (c) Thrombotic microangiopathies: thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, scleroderma; (d) Protein abnormalities: glomerular lesions due to monoclonal IgG or IgA deposition (cryoglobulinemia, multiple myeloma, many cases without amyloidosis). The gene discussed is CD79A; the disease is systemic lupus erythematosus.