C3 glomerulopathies. A new perspective on glomerular diseases.

Membranoproliferative glomerulonephritis denotes a general pattern of glomerular injury that is easily recognised by light microscopy. With additional studies, MPGN subgrouping is possible. For example, electron microscopy resolves differences in electron-dense deposition location, while immunofluorescence typically detects the composition of electron-dense deposits. A C3 glomerulopathy (C3G) is a recently described entity, a proliferative glomerulonephritis (usually but not always), with a MPGN pattern on light microscopy, with C3 staining alone on immunofluorescence, implicating hyperactivity of the alternative complement pathway. The evaluation of C3G in a patient should focus on the complement cascade, as deregulation of the alternative pathway and terminal complement cascade underlies pathogenesis. Although there are no specific treatments currently available for C3G, a better understanding of their pathogenesis would set the stage for the possible use of anti-complement drugs, as eculizumab. In this review, we summarise the pathogenesis of the C3 glomerulopathies, focusing on the role of complement, the patient cohorts recently reported and options of treatment up to the current moment.