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There have been a number of major development in the understanding of glomerular diseases recently. Membranoproliferative glomerulonephritis (MPGN) with only C3 staining was recognized as a new entity called C3 glomerulonephritis (C3GN). C3GN and dense deposit disease (DDD) are grouped under the term C3 glomerulopathy based on the presence of C3 deposits and the underlying abnormality of alternative complement system.MPGN is morphologically categorized into 3 types: I, II(DDD) and III. The emergence of C3GN suggests a new classification scheme based on whether immune complex is detected in the glomeruli. If immune complex is present, the underlying cause must be sought out, such as hepatitis C infection and lupus. If immune complex is absence, genetic test for mutation of gene for proteins regulating alternative complement pathway or autoantibodies must be performed. However, it is possible that patients with immune complex-mediated MPGN would also have complement gene mutation and/or autoantibody.
It was suggested that atypical hemolytic uremic syndrome (aHUS) should not be grouped under C3GN. Although aHUS has abnormalities in alternative complement system, the presence of complement fragments deposition and the location of complement abnormalities differentiate C3GN from aHUS. The abnormalities of complement system in C3GN are in fluid phase while aHUS are in solid phase.
C3GN can also have overlapping glomerular lesion with acute postinfectious GN. Whenever there are unusual clinical ("nephrotic syndrome") and pathological ("lack of subepithelial hump") in a supposed acute postinfectious GN case, C3GN should be kept in mind.
