C3 glomerulopathy (C3G) is a recent description of a disease characterized by uncontrolled activation of the alternative complement pathway leading to predominantly glomerular deposition of complement C3 and C3 fragments [1–4] and characteristic histo-pathological features for membranoproliferative glomerulonephritis (MPGN). The gene discussed is C3; the disease is primary membranoproliferative glomerulonephritis.