Two male patients, with no known history of autoimmune diseases, showed evidence of rich IF on renal biopsy (IgG, IgA, IgM and complement) and positive circulating autoantibodies (both patients had positive ANA and anti-dsDNA, one showed low serum C3 and C4): no clinical evidence of systemic autoimmune disease were found at time of diagnosis. This evidence concerns the gene C3 and autoimmune disease.