It is necessary to perform the following blood tests to distinguish nephrotic syndrome caused by vasculitis or connective tissue disease from other causes: antinuclear antibodies, double-stranded DNA antigens, selective antibodies to extractable nuclear antigens, complement factors (C3, C4), antinuclear cytoplasmic antibodies, as well as high-sensitivity C-reactive protein. The gene discussed is C3; the disease is vasculitis.