Reclassification of membranoproliferative glomerulonephritis: Identification of a new GN: C3GN

Abstract

This review revises the reclassification of the membranoproliferative glomerulonephritis (MPGN) after the consensus conference that by 2015 reclassified all the glomerulonephritis basing on etiology and pathogenesis, instead of the histomorphological aspects. After reclassification, two types of MPGN are to date recognized: The immunocomplexes mediated MPGN and the complement mediated MPGN. The latter type is more extensively described in the review either because several of these entities are completely new or because the improved knowledge of the complement cascade allowed for new diagnostic and therapeutic approaches. Overall the complement mediated MPGN are related to acquired or genetic cause. The presence of circulating auto antibodies is the principal acquired cause. Genetic wide association studies and family studies allowed to recognize genetic mutations of different types as causes of the complement dysregulation. The complement cascade is a complex phenomenon and activating factors and regulating factors should be distinguished. Genetic mutations causing abnormalities either in activating or in regulating factors have been described. The diagnosis of the complement mediated MPGN requires a complete study of all these different complement factors. As a consequence, new therapeutic approaches are becoming available. Indeed, in addition to a nonspecific treatment and to the immunosuppression that has the aim to block the auto antibodies production, the specific inhibition of complement activation is relatively new and may act either blocking the C5 convertase or the C3 convertase. The drugs acting on C3 convertase are still in different phases of clinical development and might represent drugs for the future. Overall the authors consider that one of the principal problems in finding new types of drugs are both the rarity of the disease and the consequent poor interest in the marketing and the lack of large international cooperative studies.

Keywords: Glomerulonephritis reclassification; Dense deposit disease; Membranoproliferative glomerulonephritis; C3 glomerulopathies; Targeting complement pathways; Complement dysregulation

Core tip: The complement pathway dysregulation has been recognized as the main cause of some membranoproliferative glomerulonephritis (MPGNs). This fact is at the basis of the new classification of the disease and of the findings of new entities as the complement factor H related protein nephropathy. Genetic studies as well as improvement in proteomics allowed recognizing the complement dysregulation as the cause of some renal diseases as the MPGN and the atypical hemolytic uremic syndrome that may be considered as strictly related diseases. The anti-complement drugs represent a new approach in the treatment of these diseases and their use in larger evidence based randomized trials is required.