C3 and Dowling-Degos disease 1: It is defined as a kind of kidney disease with only C3 deposition or weak positive deposition of immunoglobulin and/or Clq in renal tissue, including C3 glomerulonephritis (C3GN) and dense deposition disease (DDD).[1] All C3G except DDD are classified as C3GN, including type I membranoproliferative glomerulonephritis (MPGN) and complement H factor related protein 5 nephropathy which are mainly C3 deposition, familial type III MPGN, etc. C3GN was first reported by VB in 1974.[2] It was described that only complement C3 was deposited, and immunoglobulin and C1q were negative.