Primary glomerulonephritis with isolated C3 deposits: a new entity which shares common genetic risk factors with haemolytic uraemic syndrome

Complement regulator CD46: genetic variants and disease associations

Membrane cofactor protein (MCP; CD46) is an ubiquitously expressed complement regulatory protein that protects host cells from injury by complement. This type-I membrane glycoprotein serves as a cofactor for the serine protease factor I to mediate inactivation of C3b and C4b deposited on host cells. More than 60 disease-associated mutations in MCP have now been identified. The majority of the mutations are linked to a rare thrombotic microangiopathic-based disease, atypical hemolytic uremic syndrome (aHUS), but new putative links to systemic lupus erythematosus, glomerulonephritis, and pregnancy-related disorders among others have also been identified. This review summarizes our current knowledge of disease-associated mutations in this complement inhibitor.

Efficacy of Targeted Complement Inhibition in Experimental C3 Glomerulopathy

C3 glomerulopathy refers to renal disorders characterized by abnormal accumulation of C3 within the kidney, commonly along the glomerular basement membrane (GBM). C3 glomerulopathy is associated with complement alternative pathway dysregulation, which includes functional defects in complement regulator factor H (FH). There is no effective treatment for C3 glomerulopathy. We investigated the efficacy of a recombinant mouse protein composed of domains from complement receptor 2 (CR2) and FH (CR2-FH) in two models of C3 glomerulopathy with either preexisting or triggered C3 deposition along the GBM. FH-deficient mice spontaneously develop renal pathology associated with abnormal C3 accumulation along the GBM and secondary plasma C3 deficiency. CR2-FH partially restored plasma C3 levels in FH-deficient mice 2 hours after intravenous injection. CR2-FH specifically targeted glomerular C3 deposits, reduced the linear C3 reactivity assessed with anti-C3 and anti-C3b/iC3b/C3c antibodies, and prevented further spontaneous accumulation of C3 fragments along the GBM. Reduction in glomerular C3d and C9/C5b-9 reactivity was observed after daily administration of CR2-FH for 1 week. In a second mouse model with combined deficiency of FH and complement factor I, CR2-FH prevented de novo C3 deposition along the GBM. These data show that CR2-FH protects the GBM from both spontaneous and triggered C3 deposition in vivo and indicate that this approach should be tested in C3 glomerulopathy.

Paraffin immunofluorescence in the renal pathology laboratory: more than a salvage technique

Immunofluorescence studies on paraffin-embedded tissue after Pronase digestion (paraffin immunofluorescence) is used as a salvage technique in renal pathology, when frozen tissue for routine immunofluorescence is inadequate. We have recently found that it is also useful in rare cases in which the immune deposits are 'masked' on routine immunofluorescence, giving false-negative staining by routine immunofluorescence and positive staining by paraffin immunofluorescence. This study aims to evaluate the role of paraffin immunofluorescence in clinical practice with emphasis on its utility to avoid misdiagnosis of cases with masked immune complex deposits. Paraffin immunofluorescence was used in 304 (6.1%) of 4969 native biopsies reviewed from our files. In 207 (68.1%) cases, paraffin immunofluorescence was used as a salvage technique. It was necessary for diagnosis in 24 (11.6%) and had a significant contribution in 63 (30.4%) of these cases. Paraffin immunofluorescence was used to evaluate masked deposits in 97 (31.9%) cases. In 61 (62.9%) of these cases it was used to evaluate masked immune complex glomerular deposits, and in 36 cases (37.1%) it was used to evaluate masked paraproteins. Of the cases where immune complex deposits were sought, paraffin immunofluorescence was necessary for diagnosis in 16 (26.2%) cases and had a significant contribution in 4 (6.6%) cases. Fourteen of the 20 cases with masked deposits had C3 dominant stain by routine immunofluorescence, which could have been misdiagnosed as C3 glomerulopathy. Overall, paraffin immunofluorescence was necessary or had a significant contribution to diagnosis in >1/3 of the cases and is a valuable technique in renal pathology.

C4d as a Diagnostic Tool in Proliferative GN

Proliferative GN is classified as immune complex-mediated or complement-mediated (C3 glomerulopathy). Immune complex-mediated GN results from glomerular deposition of immune-complexes/Ig and C3; the C3 is derived from activation of the classical and/or lectin pathways of complement. C3 glomerulopathy results from deposition of C3 and other complement fragments with minimal or no deposition of immune complexes/Ig; the C3 is derived from activation of the alternative pathway of complement. C4d is a byproduct of activation of the classic and lectin pathways. Although widely used as a marker for antibody-mediated rejection, the significance of C4d in C3 glomerulopathy is undetermined. We studied glomerular C4d staining in 18 biopsy specimens of immune-complex GN, 30 biopsy specimens of C3 GN, and 13 biopsy specimens of postinfectious GN. All specimens of immune complex-mediated GN, except two specimens of IgA nephropathy and one specimen of sclerosing membranoproliferative GN, showed bright (2-3+) C4d staining. The staining pattern of C4d mirrored the staining patterns of Ig and C3. Conversely, C4d staining was completely negative in 24 (80%) of 30 specimens of C3 glomerulopathy, and only trace/1+ C4d staining was detected in six (20%) specimens. With regard to postinfectious GN, C4d staining was negative in six (46%) of 13 specimens, suggesting an abnormality in the alternative pathway, and it was positive in seven (54%) specimens. To summarize, C4d serves as a positive marker for immune complex-mediated GN but is absent or minimally detected in C3 glomerulopathy.

Complement genetics and susceptibility to inflammatory disease. Lessons from genotype-phenotype correlations

Different genome-wide linkage and association studies performed during the last 15 years have associated mutations and polymorphisms in complement genes with different diseases characterized by tissue damage and inflammation. These are complex disorders in which genetically susceptible individuals usually develop the pathology as a consequence of environmental triggers. Although complement dysregulation is a common feature of these pathologies, how the disease phenotype is determined is only partly understood. One way to advance understanding is to focus the research in the analysis of the peculiar genotype-phenotype correlations that characterize some of these diseases. I will review here how understanding the functional consequences of these disease-associated complement genetic variants is providing us with novel insights into the underpinning complement biology and a better knowledge of the pathogenic mechanisms underlying each of these pathologies. These advances have important therapeutic and diagnostic implications.

Complement involvement in kidney diseases: From physiopathology to therapeutical targeting

Complement cascade is involved in several renal diseases and in renal transplantation. The different components of the complement cascade might represent an optimal target for innovative therapies. In the first section of the paper the authors review the physiopathology of complement involvement in renal diseases and transplantation. In some cases this led to a reclassification of renal diseases moving from a histopathological to a physiopathological classification. The principal issues afforded are: renal diseases with complement over activation, renal diseases with complement dysregulation, progression of renal diseases and renal transplantation. In the second section the authors discuss the several complement components that could represent a therapeutic target. Even if only the anti C5 monoclonal antibody is on the market, many targets as C1, C3, C5a and C5aR are the object of national or international trials. In addition, many molecules proved to be effective in vitro or in preclinical trials and are waiting to move to human trials in the future.

The role of complement in C3 glomerulopathy

C3 glomerulopathy describes a spectrum of disorders with glomerular pathology associated with C3 cleavage product deposition and with defective complement action and regulation (Fakhouri et al., 2010; Sethi et al., 2012b). Kidney biopsies from these patients show glomerular accumulation or deposition of C3 cleavage fragments, but no or minor deposition of immunoglobulins (Appel et al., 2005; D'Agati and Bomback, 2012; Servais et al., 2007; Sethi and Fervenza, 2011). At present the current situation asks for a better definition of the underlining disease mechanisms, for precise biomarkers, and for a treatment for this disease. The complement system is a self activating and propelling enzymatic cascade type system in which inactive, soluble plasma components are activated spontaneously and lead into an amplification loop (Zipfel and Skerka, 2009). Activation of the alternative pathway is spontaneous, occurs by default, and cascade progression leads to amplification by complement activators. The system however is self-controlled by multiple regulators and inhibitors, like Factor H that control cascade progression in fluid phase and on surfaces. The activated complement system generates a series of potent effector components and activation products, which damage foreign-, as well as modified self cells, recruit innate immune cells to the site of action, coordinate inflammation and the response of the adaptive immune system in form of B cells and T lymphocytes (Kohl, 2006; Medzhitov and Janeway, 2002; Ogden and Elkon, 2006; Carroll, 2004; Kemper and Atkinson, 2007; Morgan, 1999; Muller-Eberhard, 1986; Ricklin et al., 2010). Complement controls homeostasis and multiple reactions in the vertebrate organism including defense against microbial infections (Diaz-Guillen et al., 1999; Mastellos and Lambris, 2002; Nordahl et al., 2004; Ricklin et al., 2010). In consequence defective control of the spontaneous self amplifying cascade or regulation is associated with numerous human disorders (Ricklin and Lambris, 2007; Skerka and Zipfel, 2008; Zipfel et al., 2006). Understanding the exact action and regulation of this sophisticated homeotic cascade system is relevant to understand disease pathology of various complement associated human disorders. Furthermore this knowledge is relevant for a better diagnosis and appropriate therapy. At present diagnosis of C3 glomerulopathy is primarily based on the kidney biopsy, and histological, immmunohistological and electron microscopical evaluation (D'Agati and Bomback, 2012; Fakhouri et al., 2010; Medjeral-Thomas et al., 2014a,b; Sethi et al., 2012b). The challenge is to define the actual cause of the diverse glomerular changes or damages, to define how C3 deposition results in the reported glomerular changes, the location of the cell damage and the formation of deposits.

Anti-factor H autoantibodies in C3 glomerulopathies and in atypical hemolytic uremic syndrome: one target, two diseases

Autoantibodies targeting factor H (FH), which is a main alternative complement pathway regulatory protein, have been well characterized in atypical hemolytic uremic syndrome (aHUS) but have been less well described in association with alternative pathway-mediated glomerulopathies (GP). In this study, we studied 17 patients presenting with GP who were positive for anti-FH IgG. Clinical data were collected and biological characteristics were compared with those of patients presenting with anti-FH Ab-associated aHUS. In contrast to the aHUS patients, the GP patients had no circulating FH-containing immune complexes, and their anti-FH IgG had a weaker affinity for FH. Functional studies demonstrated that these Abs induced no perturbations in FH cell surface protection or the binding of FH to its ligand. However, anti-FH IgG samples isolated from three patients were able to affect the factor I cofactor activity of FH. Epitope mapping identified the N-terminal domain of FH as the major binding site for GP patient IgG. No homozygous deletions of the CFHR1 and CFHR3 genes, which are frequently associated with the anti-FH Ab in aHUS patients, were found in the GP patients. Finally, anti-FH Abs were frequently associated with the presence of C3 nephritic factor in child GP patients and with monoclonal gammopathy in adult GP patients, who frequently showed Ig Lchain restriction during reactivity against factor H. These data provide deeper insights into the pathophysiological differences between aHUS and GP, demonstrating heterogeneity of anti-FH IgG.

Clinico-pathologic spectrum of C3 glomerulopathy-an Indian experience

Background

C3 glomerulopathy (C3GP) is characterized by deposition of complement C3 with absence/traces of immunoglobulins in the glomeruli and categorized into dense deposit disease (DDD), C3 glomerulonephritis (C3GN), complement factor H related protein 5(CFHR5) nephropathy etc. Collaborative efforts of pathologists, complement biologists and nephrologists worldwide are expanding the histomorphological pattern and laboratory findings related to C3GP. Hence, we studied point prevalence and morphological spectrum of C3GP in Indian patients to correlate morphological patterns with standard therapies and outcome of the patients.

Methods

Retrospective analysis of renal biopsies (2007-2012,n-4565), which on immunofluorescence (IF) had C3 dominant deposits with absence or trace amount of immunoglobulin was carried out. Histopathology and electronmicroscopy (EM) were reviewed; cases were re-classified as DDD and C3GN. Histomorphological patterns of both groups were compared and correlated with treatment. Clinical details and follow up of patients were retrieved from the department of nephrology.

Results

There were 31 cases (0.7%) of C3GP sub-classified as DDD (n-13) and C3GN (n-14). It was difficult to sub-classify 4 cases since EM showed overlapping features. C3GN and DDD had distinct clinical characteristics and disease outcome, though pathological features were overlapping. Majority of C3GP patients were males and were in 2^nd to 4^th decade of life. Nephrotic syndrome in DDD and nephritic-nephrotic presentation in C3GN patients was more common.

Hypertension and oliguria were more often observed in C3GN than DDD. Membranoproliferative pattern (MPGN) was commonest pattern in DDD; other patterns seen were mesangial proliferative, mesangial expansive/nodular, exudative and crescentic. C3GN also had all the above patterns, the predominant ones being MPGN and mesangial proliferative. Limited follow-up revealed response to therapy only in C3GN (33%). Progression to ESRD was 33% in DDD and 10% cases in C3GN.

Conclusion

C3GP comprise 0.7% of all renal biopsies. MPGN pattern was the commonest morphological pattern in DDD whereas MPGN and mesangial proliferative pattern were equally dominant patterns in C3GN. EM of 4 cases (13%) showed intermediate features. Evaluation of alternate complement pathway must be done in all cases to identify the point of dysregulated alternate complement pathway and to confirm the diagnosis in ambiguous cases.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1730070964135632

Current Understanding of the Role of Complement in IgA Nephropathy

Complement activation has a role in the pathogenesis of IgA nephropathy, an autoimmune disease mediated by pathogenic immune complexes consisting of galactose-deficient IgA1 bound by antiglycan antibodies. Of three complement-activation pathways, the alternative and lectin pathways are involved in IgA nephropathy. IgA1 can activate both pathways in vitro, and pathway components are present in the mesangial immunodeposits, including properdin and factor H in the alternative pathway and mannan-binding lectin, mannan-binding lectin-associated serine proteases 1 and 2, and C4d in the lectin pathway. Genome-wide association studies identified deletion of complement factor H-related genes 1 and 3 as protective against the disease. Because the corresponding gene products compete with factor H in the regulation of the alternative pathway, it has been hypothesized that the absence of these genes could lead to more potent inhibition of complement by factor H. Complement activation can take place directly on IgA1-containing immune complexes in circulation and/or after their deposition in the mesangium. Notably, complement factors and their fragments may serve as biomarkers of IgA nephropathy in serum, urine, or renal tissue. A better understanding of the role of complement in IgA nephropathy may provide potential targets and rationale for development of complement-targeting therapy of the disease.

Incidence and profile of C3 Glomerulopathy: A single center study

C3 glomerulopathy has recently been described as a distinct entity. The underlying mechanism is unregulated activation of the alternate pathway of the complement system. The most common presentation is with an acute nephritic syndrome. The diagnosis is made on immunofluoroscence by the presence of isolated or dominant C3 staining. In this retrospective study, renal biopsy data were collected from 2010 to 2013 patients with C3 glomerulopathy identified and their clinical and biochemical parameters analyzed. Out of 514 biopsies available for analysis, the incidence of C3 glomerulopathy was 1.16% (n = 6). The mean age of the presentation was 26 years and the average estimated glomerular filtration rate was 30.65 ml/min/1.73 m(2). The most common histopathological pattern was membranoproliferative glomerulonephritis (n = 4).

Glomerulonefritis C3: una nueva categoría de glomerulonefritis con implicaciones etiopatogénicas

Introducción: las glomerulonefritis con depósitos exclusivos de la fracción C3 del complemento (GN-C3) pueden implicar alteración en la vía alterna de este. Objetivos: describir retrospectivamente una serie de casos de GN-C3 y determinar la frecuencia con que los pacientes continúan con alteraciones renales y/o hipocomplementemia. Métodos: se evaluaron las características histológicas y clínicas y la evolución de los 22 casos de GN-C3 diagnosticados entre 2004 y 2012 en el Departamento de Patología (Facultad de Medicina, Universidad de Antioquia). Resultados: 14 de los pacientes fueron niños y 12 fueron hombres; la mediana de edad fue de 13 años (rango: 3-65). Diez se presentaron como síndrome nefrítico, siete como GN rápidamente progresiva, tres como insuficiencia renal aguda, uno como insuficiencia renal crónica y uno como síndrome nefrótico-nefrítico; 21 tenían hipocomplementemia C3. Todas las biopsias mostraron GN proliferativa. Ocho pacientes tuvieron remisión completa; cuatro, alteraciones persistentes del uroanálisis; seis desarrollaron enfermedad renal crónica, en cinco de ellos terminal; en cuatro no hubo seguimiento. En nueve pacientes hubo seguimiento de los niveles séricos de C3 y en todos ellos se normalizaron entre 1 y 3 meses después de la biopsia. Conclusiones: las GN-C3 pueden producir alteraciones renales persistentes o recurrentes y evolucionar a la insuficiencia renal terminal. Es recomendable el seguimiento clínico a largo plazo, con mediciones repetidas de los niveles de C3.

Current concepts in C3 glomerulopathy

Complement component 3 glomerulopathy (C3G) is a recently defined entity comprising of dense deposit disease and C3 glomerulonephritis. The key histological feature is the presence of isolated C3 deposits without immunoglobulins. Often masqueradng as some of the common glomerulonephritides this is a prototype disorder occurring from dysregulated alternate complement pathway with recently identified genetic defects and autoantibodies. We review the pathophysiology, clinical features, and diagnostic and treatment strategies.

Reanalysis of membranoproliferative glomerulonephritis patients according to the new classification: a multicenter study

BACKGROUND

All types of membranoproliferative glomerulonephritis (MPGN) are progressive diseases with poor prognoses. Recently, a newly proposed classification of these diseases separated them into immune complex- and complement-mediated diseases. We investigated the frequency of C3 glomerulonephritis among previously diagnosed MPGN patients.

METHODS

We conducted a retrospective study of patients diagnosed with MPGN at three tertiary care institutions between 2001 and 2010. We investigated the incidence of complement-mediated disease among patients diagnosed with MPGN. Progressive renal dysfunction was defined as a 50% reduction in the glomerular filtration rate or the need for renal replacement therapy.

RESULTS

Among the 3,294 renal biopsy patients, 77 (2.3%) were diagnosed with MPGN; 31 cases were excluded, of which seven were diagnosed with systemic lupus nephritis, and the others were not followed for a minimum of 12 months after biopsy. Based on the new classification, complement-mediated MPGN was diagnosed in two patients (4.3%); only one patient developed progressive renal dysfunction. Among the immune complex-mediated MPGN patients, 17 patients developed progressive renal dysfunction. Serum albumin and creatinine levels at the time of MPGN diagnosis were risk factors of renal deterioration, after adjusting for low C3 levels and nephrotic syndrome.

CONCLUSION

Complement-mediated glomerulonephritis was present in 4.3% of patients previously diagnosed with MPGN.

Eculizumab in the treatment of membranoproliferative glomerulonephritis

A major shift in our understanding of the membranoproliferative glomerulonephritis (MPGN) lesion is the focus on which components of the complement pathway are involved in mediating renal injury. Hence, MPGN is no longer classified solely by ultrastructural findings on biopsy but instead divided into immune complex-mediated lesions versus complement-mediated lesions. This emphasis on complement, in turn, leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anticomplement therapy, blocks at the level of C5 and has revolutionized the treatment of complement-mediated diseases such as paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous complement-mediated MPGN lesions, also known as C3 glomerulopathy, remains unclear. To date, the experience and published data on using eculizumab in MPGN suggests this agent will work for some, but not all, patients with this pathologic lesion.

New functional and structural insights from updated mutational databases for complement factor H, Factor I, membrane cofactor protein and C3

aHUS (atypical haemolytic uraemic syndrome), AMD (age-related macular degeneration) and other diseases are associated with defective AP (alternative pathway) regulation. CFH (complement factor H), CFI (complement factor I), MCP (membrane cofactor protein) and C3 exhibited the most disease-associated genetic alterations in the AP. Our interactive structural database for these was updated with a total of 324 genetic alterations. A consensus structure for the SCR (short complement regulator) domain showed that the majority (37%) of SCR mutations occurred at its hypervariable loop and its four conserved Cys residues. Mapping 113 missense mutations onto the CFH structure showed that over half occurred in the C-terminal domains SCR-15 to -20. In particular, SCR-20 with the highest total of affected residues is associated with binding to C3d and heparin-like oligosaccharides. No clustering of 49 missense mutations in CFI was seen. In MCP, SCR-3 was the most affected by 23 missense mutations. In C3, the neighbouring thioester and MG (macroglobulin) domains exhibited most of 47 missense mutations. The mutations in the regulators CFH, CFI and MCP involve loss-of-function, whereas those for C3 involve gain-of-function. This combined update emphasizes the importance of the complement AP in inflammatory disease, clarifies the functionally important regions in these proteins, and will facilitate diagnosis and therapy.

A new compilation of 324 mutations in four major proteins from the complement alternative pathway reveals mutational hotspots in factor H and complement C3, and less so in factor I and membrane cofactor protein. Their associations with function are discussed.

Making sense of the spectrum of glomerular disease associated with complement dysregulation

Over recent years, complement has emerged as a major player in the development of a number of glomerular diseases, including atypical haemolytic uraemic syndrome, membranoproliferative glomerulonephritis and the recently described C3 glomerulonephritis. Some patients and pedigrees show overlapping features of these conditions. Intriguingly, a few complement gene mutations are common to different disease phenotypes. In this review, we explore the evidence for complement dysregulation in these diseases and the clinical interface between them, and present a hypothesis to explain the variable phenotype associated with dysregulation of the alternative complement pathway.

Anti-complement therapy for glomerular diseases

A major shift in our understanding of glomerular diseases is the focus on which components of the complement pathway are involved in mediating kidney injury. For example, the membranoproliferative glomerulonephritis lesion is no longer classified solely by ultrastructural findings on biopsy and is now divided into immune-complex-mediated lesions vs complement-mediated lesions. In turn, this emphasis on complement leads to interest in therapies that target complement as potential disease-modifying agents. Eculizumab, the first available anti-complement therapy, blocks at the level of C5 and has revolutionized the treatment of atypical hemolytic uremic syndrome. Whether this agent will work equally well for the far more heterogeneous entities of C3 glomerulonephritis and dense deposit disease remains unclear. Instead, newer agents that target C3 may turn out to be the most effective and specific therapy for these C3 glomerulopathies.

[C3 glomerulopathy]

C3 glomerulopathy is an heterogeneous group of glomerular diseases associated with acquired or genetic abnormalities of complement alternative pathway (AP) components. It is characterized by predominant C3 deposits in the mesangium and along the glomerular basement membrane (GBM). Presenting features comprise proteinuria (sometimes with nephritic syndrome), haematuria, hypertension and renal failure. C3 glomerulopathy have a poor renal prognosis with progression to end stage renal disease (ESRD) in 50% of cases during the first decade after initial presentation. Moreover, C3 deposits recur in most of cases after renal transplantation. Patients frequently have low serum C3 level attributed to the activation of the alternative pathway of complement. Animal models have confirmed the role of excessive C3 activation in the pathogenesis of C3 glomerulopathy. To date, the optimal treatment remains unknown. It is currently based on the use of angiotensin-converting-enzyme inhibitors (ACEI) and angiotensin II-receptor blockers (ARB), sometimes associated with immunosuppressive therapy. Blockade of C5a release with eculizumab, a monoclonal anti-C5 antibody, may be of particular interest in the treatment of C3G.

Membranoproliferative glomerulonephritis associated with autoimmune diseases

Membranoproliferative glomerulonephritis (MPGN) has been classified based on its pathogenesis into immune complex-mediated and complement-mediated MPGN. The immune complex-mediated type is secondary to chronic infections, autoimmune diseases or monoclonal gammopathy. There is a paucity of data on MPGN associated with autoimmune diseases. We reviewed the Mayo Clinic database over a 10-year period and identified 12 patients with MPGN associated with autoimmune diseases, after exclusion of systemic lupus erythematosus. The autoimmune diseases included rheumatoid arthritis, primary Sjögren's syndrome, undifferentiated connective tissue disease, primary sclerosing cholangitis and Graves' disease. Nine of the 12 patients were female, and the mean age was 57.9 years. C4 levels were decreased in nine of 12 patients tested. The serum creatinine at time of renal biopsy was 2.2 ± 1.0 mg/dl and the urinary protein was 2,850 ± 3,543 mg/24 h. Three patients required dialysis at the time of renal biopsy. Renal biopsy showed an MPGN in all cases, with features of cryoglobulins in six cases; immunoglobulin (Ig)M was the dominant Ig, and both subendothelial and mesangial electron dense deposits were noted. Median follow-up was 10.9 months. Serum creatinine and proteinuria improved to 1.6 ± 0.8 mg/dl and 428 ± 677 mg/24 h, respectively, except in 3 patients with end-stage renal disease. In summary, this study describes the clinical features, renal biopsy findings, laboratory evaluation, treatment and prognosis of MPGN associated with autoimmune diseases.

New trends of an old disease: the acute post infectious glomerulonephritis at the beginning of the new millenium

The association between acute renal disease and infection has been known since the mid '800s: acute post-infectious glomerulonephritis (PIGN) is a reactive immunological process against the kidney secondary to an infection, classically caused by a Streptococcus. The typical clinical presentation of PIGN is an acute nephritic syndrome with macro- or microscopic hematuria, proteinuria, hypertension, edema and renal function impairment of variable degree. The histology is characterized by an intracapillary glomerular proliferation, but may rarely be associated with an extracapillary proliferation. The classical childhood form is still present nowadays, even with severe cases, in developing countries, while in the last decades it almost disappeared in industrialized countries, where post-infectious GN are often found in elderly patients with multiple comorbidities. These clinical variants are usually related to other infective agents, like Staphylococcus aureus, both methicillin resistant (MRSA) and susceptible, and may be characterized by an IgA-dominant deposition. Kidney biopsy is rarely needed, especially in the child, while in the adult or old patient a biopsy is warranted if there is an atypical presentation or evolution, like rapidly progressive renal failure, absent or delayed function recovery, persisting low C3, nephrotic range proteinuria and persisting high proteinuria. Current therapy strategies rely on culture-guided systemic antibiotics, especially in the old patient, in which MRSA are relatively frequent, support therapy and only in very selected cases on steroids. These latter cases include the rare PIGN with crescents and those with a severe interstitial inflammation.

Membranous-like glomerulopathy with masked IgG kappa deposits

The diagnostic classification of glomerulonephritis is determined by the interplay of changes seen using light, immunofluorescence, and electron microscopy of the renal biopsy. Routine direct immunofluorescence on fresh tissue is currently considered the gold standard for the detection and characterization of immune deposits. We recently found a peculiar form of glomerular immune complex deposition in which masked deposits required an antigen-retrieval step to be visualized. Over a 2-year period, 14 cases were characterized by numerous, large subepithelial deposits visualized by electron microscopy and C3-predominant staining by routine immunofluorescence on fresh tissue with weak to negative immunoglobulin staining. Repeat immunofluorescence after digestion of the formalin-fixed paraffin-embedded tissue with pronase elicited strong IgG-κ staining restricted within the deposits. The patients were often young with a mean age of 26 years and commonly had clinical evidence of vague autoimmune phenomenon. The clinicopathologic findings in this unusual form of glomerulopathy do not fit neatly into any currently existing diagnostic category. We have termed this unique form of glomerulopathy membranous-like glomerulopathy with masked IgG-κ deposits.

Update on membranoproliferative GN

Membranoproliferative GN represents a pattern of injury seen on light microscopy. Historically, findings on electron microscopy have been used to further subclassify this pathologic entity. Recent advances in understanding of the underlying pathobiology have led to a proposed classification scheme based on immunofluorescence findings. Dysregulation of the complement system has been shown to be a major risk factor for the development of a membranoproliferative GN pattern of injury on kidney biopsy. Evaluation and treatment of this complex disorder rest on defining the underlying mechanisms.

C3 nephritic factor associated with C3 glomerulopathy in children

BACKGROUND

C3 glomerulopathy (C3G) is characterized by predominant C3 deposits in glomeruli and dysregulation of the alternative pathway of complement. Half of C3G patients have a C3 nephritic factor (C3NeF). C3G incorporated entities with a range of features on microscopy including dense deposit diseases (DDD) and C3 glomerulonephritis (C3GN). The aim of this work was to study children cases of C3G associated with C3NeF.

METHODS

We reviewed 18 cases of C3G with a childhood onset associated with C3NeF without identified mutations in CFH, CFI, and MCP genes.

RESULTS

Clinical histories started with recurrent hematuria for seven patients, nephrotic syndrome for four, acute post-infectious glomerulonephritis for three and acute renal failure for four. Twelve patients had a low C3 at first investigation. Kidney biopsy showed ten C3GN and eight DDD. Twenty-three percent of the patients tested presented elevated sC5b9. Seven patients relapsed 3 to 6 years after the onset. At the end of follow-up, two patients were under dialysis, 11 had a persistent proteinuria, five had none; four patients did not follow any treatment. Steroids were first used in 80 % of cases.

CONCLUSIONS

C3NeF associated C3G has a heterogeneous presentation and outcome. Anti-proteinuric agents may control the disease during follow-up, even after nephrotic syndrome at the onset. The efficiency of immunosuppressive therapy remains questionable.

An emerging molecular understanding and novel targeted treatment approaches in pediatric kidney diseases

The evaluation and treatment of the heterogeneous group of kidney diseases poses a challenging field in pediatrics. Many of the pediatric disorders resulting in severe renal affection are exceedingly rare and therapeutic approaches have remained symptomatic for most of these disease entities. The insights obtained from cellular and molecular studies of rare disorders by recent genetic studies have now substantially changed our mechanistic understanding of various important pediatric renal diseases and positive examples of targeted treatment approaches are emerging. Three fields of recent breathtaking developments in pediatric nephrology are the pathophysiology of nephrotic syndrome and proteinuria, the molecular mechanisms underlying atypical hemolytic uremic syndrome, and the genetics and cellular biology of inherited cystic kidney diseases. In all three areas, the combined power of molecular basic science together with deeply characterizing clinical approaches has led to the establishment of novel pathophysiological principles and to the first clinical trials of targeted treatment approaches.

Clinical findings, pathology, and outcomes of C3GN after kidney transplantation

C3 glomerulonephritis (C3GN) results from abnormalities in the alternative pathway of complement, and it is characterized by deposition of C3 with absent or scant Ig deposition. In many patients, C3GN progresses to ESRD. The clinical features, pathology, and outcomes of patients with C3GN receiving kidney transplantation are unknown. Between 1996 and 2010, we identified 21 patients at our institution who received a kidney transplant because of ESRD from C3GN. The median age at the time of initial diagnosis of C3GN at kidney biopsy was 20.8 years. The median time from native kidney biopsy to dialysis or transplantation was 42.3 months. Of 21 patients, 14 (66.7%) patients developed recurrent C3GN in the allograft. The median time to recurrence of disease was 28 months. Graft failure occurred in 50% of patients with recurrent C3GN, with a median time of 77 months to graft failure post-transplantation. The remaining 50% of patients had functioning grafts, with a median follow-up of 73.9 months. The majority of patients had hematuria and proteinuria at time of recurrence. Three (21%) patients were positive for monoclonal gammopathy and had a faster rate of recurrence and graft loss. Kidney biopsy at the time of recurrence showed mesangial proliferative GN in eight patients and membranoproliferative GN in six patients. All allograft kidney biopsies showed bright C3 staining (2-3+), with six biopsies also showing trace/1+ staining for IgM and/or IgG. To summarize, C3GN recurs in 66.7% of patients, and one half of the patients experience graft failure caused by recurrence.

A novel CFHR5 mutation associated with C3 glomerulonephritis in a Turkish girl

C3 glomerulopathy defines a subgroup of membranoproliferative glomerulonephritis (MPGN) characterized by complement 3 (C3)-positive, immunoglobulin-negative deposits in immunofluorescence microscopy. It comprises 3 clinical conditions: dense deposit disease, C3 glomerulonephritis, and complement factor H-related 5 (CFHR5) nephropathy. Mutations in genes encoding regulatory proteins of the alternative complement pathway have been described. A 16-year-old girl was admitted to the hospital due to periorbital edema. Nephrotic syndrome accompanied by low C3 level was diagnosed. Renal biopsy showed MPGN in light microscopy, only C3 deposits in immunofluorescence microscopy, and subendothelial electron dense deposits and capillary basement membrane thickening with double contour formation in electron microscopy. C3 nephritic factor and anti complement factor H antibody were negative. Complement factor H level was normal. Genetic screening showed a novel heterozygous p.Cys269Arg variation in the CFHR5 gene without any mutation in CFH and CFI genes. Eculizumab therapy was started but was unsuccessful at 10 months of follow-up. We have identified a novel heterozygous variation in CFHR5-related nephropathy presenting with nephrotic syndrome and persistently low C3 level, thus expanding the genetic and phenotypic spectrum of the disease. Eculizumab seems to be ineffective in this subtype.

Nanosized contrast agents to noninvasively detect kidney inflammation by magnetic resonance imaging

Several molecular imaging methods have been developed that use nanosized contrast agents to detect markers of inflammation within tissues. Kidney inflammation contributes to disease progression in a wide range of autoimmune and inflammatory diseases, and a biopsy is currently the only method of definitively diagnosing active kidney inflammation. However, the development of new molecular imaging methods that use contrast agents capable of detecting particular immune cells or protein biomarkers will allow clinicians to evaluate inflammation throughout the kidneys and to assess a patient's response to immunomodulatory drugs. These imaging tools will improve our ability to validate new therapies and to optimize the treatment of individual patients with existing therapies. This review describes the clinical need for new methods of monitoring kidney inflammation and recent advances in the development of nanosized contrast agents for the detection of inflammatory markers of kidney disease.

Dense deposit disease and C3 glomerulopathy

C3 glomerulopathy refers to those renal lesions characterized histologically by predominant C3 accumulation within the glomerulus, and pathogenetically by aberrant regulation of the alternative pathway of complement. Dense deposit disease is distinguished from other forms of C3 glomerulopathy by its characteristic appearance on electron microscopy. The extent to which dense deposit disease also differs from other forms of C3 glomerulopathy in terms of clinical features, natural history, and outcomes of treatment including renal transplantation is less clear. We discuss the pathophysiology of C3 glomerulopathy, with evidence for alternative pathway dysregulation obtained from affected individuals and complement factor H (Cfh)-deficient animal models. Recent linkage studies in familial C3 glomerulopathy have shown genomic rearrangements in the Cfh-related genes, for which the novel pathophysiologic concept of Cfh deregulation has been proposed.

Monoclonal gammopathy-associated proliferative glomerulonephritis

Monoclonal gammopathy is characterized by circulating monoclonal immunoglobulin owing to clonal proliferation of immunoglobulin-producing B lymphocytes or plasma cells. Clonal proliferation of B lymphocytes is seen in B-cell lymphoma/leukemia, and clonal plasma cell proliferation is seen in multiple myeloma and monoclonal gammopathy of undetermined significance. The monoclonal immunoglobulin in the setting of a B-cell or plasma cell disorder can cause a proliferative glomerulonephritis via 2 mechanisms: (1) glomerular deposition of the monoclonal immunoglobulin with activation of the classical pathway of complement (direct mechanism), resulting in an immunoglobulin-positive C3-positive glomerulonephritis, and (2) glomerular deposition of complement factors of the alternative and terminal pathway via inhibition of alternative pathway-regulating proteins by the monoclonal immunoglobulin (indirect mechanism), resulting in immunoglobulin-negative C3-positive glomerulonephritis (C3 glomerulopathy). Evaluation should include serum and urine electrophoresis and immunofixation as well as serum-free light-chain assay. If a monoclonal immunoglobulin is detected on these tests, bone marrow biopsy or imaging is needed to exclude more advanced plasma cell dyscrasia. Evaluation of alternative pathway of complement should be done in patients with Ig-negative C3-positive glomerulonephritis. If monoclonal gammopathy is due to an underlying malignant disease such as myeloma, lymphoma, or chronic lymphocytic leukemia, then specific treatment should be aimed at treating the malignant disease, with the goal of eradicating the clonal cells producing the immunoglobulin. In contrast, if monoclonal gammopathy is due to a monoclonal gammopathy of undetermined significance, treatment options include bortezomib, cyclophosphamide, and dexamethasone for a non-IgM monoclonal immunoglobulin and rituximab alone or in combination with cyclophosphamide and dexamethasone for an IgM monoclonal immunoglobulin.

C3 glomerulonephritis: clinicopathological findings, complement abnormalities, glomerular proteomic profile, treatment, and follow-up

C3 Glomerulonephritis (C3GN) is a recently described disorder that typically results from abnormalities in the alternative pathway of complement. Here, we describe the clinical features, kidney biopsy findings, alternative pathway abnormalities, glomerular proteomic profile, and follow-up in 12 cases of C3GN. This disorder equally affected all ages, both genders, and typically presented with hematuria and proteinuria. In both the short and long term, renal function remained stable in the majority of patients with native kidney disease. In two patients, C3GN recurred within one year of transplantation and resulted in a decline in allograft function. Kidney biopsy mainly showed a membranoproliferative pattern; although both mesangial proliferative and diffuse endocapillary proliferative glomerulonephritis were noted. Alternative pathway abnormalities were heterogeneous; both acquired and genetic. The most common acquired abnormality was the presence of C3 nephritic factors, while the most common genetic finding was the presence of H402 and V62 alleles of Factor H. In addition to these risk factors, other abnormalities included Factor H auto-antibodies and mutations in CFH, CFI and CFHR genes. Laser dissection and mass spectrometry of glomeruli from patients with C3GN showed accumulation of alternative pathway and terminal complement complex proteins. Thus, C3GN results from diverse abnormalities of the alternative complement pathway leading to subsequent glomerular injury.

C3 glomerulopathy: what's in a name?

Whereas early classifications of membranoproliferative glomerulonephritis (MPGN) were based on morphologic features, the modern approach is directed at immunofluorescence findings. Glomerular deposits of C3 alone, without immunoglobulin, are the hallmark of alternative complement pathway dysregulation through inherited or acquired defects. These immunoglobulin-negative forms are referred to as C3 glomerulopathy, which encompasses both dense deposit disease and C3 glomerulonephritis. Distinguishing C3 glomerulopathy from immunoglobulin-mediated MPGN is opening the way to better diagnostic, prognostic, and treatment algorithms.

Eculizumab and recurrent C3 glomerulonephritis

BACKGROUND

Hyperactivity of the alternative complement pathway is the principle defect in C3 glomerulopathies (C3G). Eculizumab, a monoclonal antibody that binds C5 to prevent formation of the membrane attack complex, has been shown to be beneficial in some patients with this disease.

METHODS

In this open-label, proof-of-concept efficacy-and-safety study, a patient with the initial diagnosis of dense deposit disease (DDD) and allograft recurrence of C3 glomerulonephritis (C3GN) was treated with eculizumab every other week for 1 year. The patient had pathological evidence of C3GN and proteinuria >1 g/day at enrollment. He underwent graft biopsy before enrollment and repeat biopsy at 6 and 12 months.

RESULTS

Although no mutations were identified in complement genes, functional studies were positive for C3 nephritic factors and elevated levels of soluble membrane attack complex (sMAC). On therapy, sMAC levels normalized and although proteinuria initially decreased, it increased reaching pre-treatment levels at 12 months. Although serum creatinine remained stable, repeat allograft biopsies showed progression of disease.

CONCLUSIONS

Clinical and histopathologic data suggest a partial response to eculizumab in this patient. While eculizumab blocked activation of the terminal complement cascade, persistent dysregulation of the alternative pathway remained, indicating eculizumab alone cannot control disease in this patient. Additional research is required to identify effective anticomplement therapy for this group of C3G patients.

Molecular genetics of familial hematuric diseases

The familial hematuric diseases are a genetically heterogeneous group of monogenic conditions, caused by mutations in one of several genes. The major genes involved are the following: (i) the collagen IV genes COL4A3/A4/A5 that are expressed in the glomerular basement membranes (GBM) and are responsible for the most frequent forms of microscopic hematuria, namely Alport syndrome (X-linked or autosomal recessive) and thin basement membrane nephropathy (TBMN). (ii) The FN1 gene, expressed in the glomerulus and responsible for a rare form of glomerulopathy with fibronectin deposits (GFND). (iii) CFHR5 gene, a recently recognized regulator of the complement alternative pathway and mutated in a recently revisited form of inherited C3 glomerulonephritis (C3GN), characterized by isolated C3 deposits in the absence of immune complexes. A hallmark feature of all conditions is the age-dependent penetrance and a broad phenotypic heterogeneity in the sense that subsets of patients progress to added proteinuria or proteinuria and chronic renal failure that may or may not lead to end-stage kidney disease (ESKD) anywhere between the second and seventh decade of life. In addition to other excellent laboratory tools that assist the clinician in reaching the correct diagnosis, the molecular analysis emerges as the gold standard in establishing the diagnosis in many cases of doubt due to equivocal findings that complicate the differential diagnosis. Recent work led to the description of candidate genetic modifiers which confer a variable risk for progressing to chronic renal failure when co-inherited on the background of a primary glomerulopathy. Finally, more families are still waiting to be studied and more genes to be mapped and cloned that are responsible for other forms of heritable hematuric diseases. The study of such genes and their protein products will likely shed more light on the structure and function of the glomerular filtration barrier and other important glomerular components.

Treatment options for C3 glomerulopathy

PURPOSE OF REVIEW

The purpose of this review is to discuss emerging nomenclature, review the salient clinicopathological features and describe the therapeutic options available for the treatment of C3 glomerulopathy (C3G).

RECENT FINDINGS

C3G is minimally responsive to traditional immune suppression and randomized controlled trials to support therapy are absent. The burgeoning understanding of the role of the alternative complement pathway in C3G combined with animal data supporting the use of terminal complement blockade and a few reports suggesting that the anticomplement drug eculizumab may offer a therapeutic advantage have triggered great interest in the field of complement-mediated renal disease.

SUMMARY

Anticellular immune suppression and plasma therapy have limited efficacy in C3G. Data suggest that eculizumab may ameliorate disease in some C3G patients. The limited, recently published cohort data highlight crucial aspects of this group of diseases and support the need for extensive genetic and biomarker research to validate the pathologic mechanisms, delineate the spectrum of disease and guide the design of the rigorous trials to identify effective therapies for the treatment of C3G.

Properdin in complement activation and tissue injury

The plasma protein properdin is the only known positive regulator of complement activation. Although regarded as an initiator of the alternative pathway of complement activation at the time of its discovery more than a half century ago, the role and mechanism of action of properdin in the complement cascade has undergone significant conceptual evolution since then. Despite the long history of research on properdin, however, new insight and unexpected findings on the role of properdin in complement activation, pathogen infection and host tissue injury are still being revealed by ongoing investigations. In this article, we provide a brief review on recent studies that shed new light on properdin biology, focusing on the following three topics: (1) its role as a pattern recognition molecule to direct and trigger complement activation, (2) its context-dependent requirement in complement activation on foreign and host cell surfaces, and (3) its involvement in alternative pathway complement-mediated immune disorders and considerations of properdin as a potential therapeutic target in human diseases.

C3 glomerulonephritis associated with monoclonal gammopathy: a case series

BACKGROUND

C3 glomerulonephritis (GN) is a proliferative GN resulting from glomerular deposition of complement factors due to dysregulation of the alternative pathway of complement. Dysregulation of the alternative pathway of complement may occur as a result of mutations or functional inhibition of complement-regulating proteins. Functional inhibition of the complement-regulating proteins may result from a monoclonal gammopathy.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

32 Mayo Clinic patients with C3 GN, 10 (31%) of whom had evidence of a monoclonal immunoglobulin in serum.

OUTCOMES

Clinical features, hematologic and bone marrow biopsy findings, kidney biopsy findings, kidney measures, complement pathway abnormalities, treatment, and follow-up of patients with C3 GN that was associated with a monoclonal gammopathy.

RESULTS

Mean age of patients with C3 GN associated with monoclonal gammopathy was 54.5 years. Bone marrow biopsy done in 9 patients revealed monoclonal gammopathy of undetermined significance in 5 patients, small lymphocytic lymphoma/chronic lymphocytic leukemia in one patient, and no abnormal clones in the other 3 patients. Kidney biopsy showed membranoproliferative GN with bright capillary wall C3 staining in all 10 patients. Evaluation of the alternative pathway of complement showed abnormalities in 7 of 9 patients tested. No mutation in complement-regulating proteins was detected in any patient. As an index case, one patient with C3 GN and chronic lymphocytic leukemia was treated with rituximab, cyclophosphamide, vincristine, and prednisone, and one patient with C3 GN and monoclonal gammopathy of undetermined significance was treated with dexamethasone and bortezomib. Both patients showed significant decreases in hematuria and proteinuria and stabilization of kidney function.

LIMITATIONS

Studies to show evidence of direct activation of the alternative pathway by monoclonal immunoglobulin were not done.

CONCLUSIONS

The study highlights the association of C3 GN and monoclonal gammopathy, in particular in the older population, and the importance of targeting the underlying hematologic malignancy as an approach to treating C3 GN.

Novel roles of complement in renal diseases and their therapeutic consequences

The complement system functions as a part of the innate immune system. Inappropriate activation of the complement pathways has a deleterious effect on kidneys. Recent advances in complement research have provided new insights into the pathogenesis of glomerular and tubulointerstitial injury associated with complement activation. A new disease entity termed 'C3 glomerulopathy' has recently been proposed and is characterized by isolated C3 deposition in glomeruli without positive staining for immunoglobulins. Genetic and functional studies have demonstrated that several different mutations and disease variants, as well as the generation of autoantibodies, are potentially associated with its pathogenesis. The data from comprehensive analyses suggest that complement dysregulation can also be associated with hemolytic uremic syndrome and more common glomerular diseases, such as IgA nephropathy and diabetic kidney disease. In addition, animal studies utilizing genetically modified mice have begun to elucidate the molecular pathomechanisms associated with the complement system. From a diagnostic point of view, a noninvasive, MRI-based method for detecting C3 has recently been developed to serve as a novel tool for diagnosing complement-mediated kidney diseases. While novel therapeutic tools related to complement regulation are emerging, studies evaluating the precise roles of the complement system in kidney diseases will still be useful for developing new therapeutic approaches.

Eculizumab in the treatment of atypical haemolytic uraemic syndrome and other complement-mediated renal diseases

PURPOSE OF REVIEW

This review considers the use of eculizumab in the treatment of atypical haemolytic uraemic syndrome (aHUS) as well as the other complement-mediated renal diseases, including dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). In addition, a brief discussion of the effectiveness of eculizumab for the prevention of antibody-mediated rejection (AMR) in the setting of renal transplant and the treatment of shiga toxin associated haemolytic uraemic syndrome (STEC HUS) is also provided.

RECENT FINDINGS

No randomized controlled trials exist to support the use of eculizumab in renal disease. The results of two unpublished, prospective adult and adolescent trials support its utility in aHUS, whereas retrospective data support the effectiveness in paediatric aHUS. These two data sets form the basis of the sole renal indication for eculizumab. One small, single-centre trial and a growing number of case reports support the use of eculizumab in C3 glomerulopathy (C3G). There are limited trial data in AMR and renal transplant. Finally, there are conflicting data for the use of eculizumab in STEC HUS.

SUMMARY

The cumulative published data establish the effectiveness of eculizumab in a select group of renal diseases that have at the centre of their disease either abnormal complement control or maladaptive complement activation.

American Society of Nephrology Quiz and Questionnaire 2012: glomerulonephritis

Presentation of the Nephrology Quiz and Questionnaire (NQQ) has become an annual tradition at the meetings of the American Society of Nephrology. It is a very popular session, judged by consistently large attendance. Members of the audience test their knowledge and judgment on a series of case-oriented questions prepared and discussed by experts. They can also compare their answers in real time, using audience response devices, to those of program directors of nephrology training programs in the United States, acquired through an Internet-based questionnaire. The topic presented here is GN. Cases representing this category, along with single best answer questions, were prepared by a panel of experts (Drs. Fervenza, Glassock, and Bleyer). The correct and incorrect answers were then briefly discussed after the audience responses and the results of the questionnaire were displayed. This article recapitulates the session and reproduces its educational value for a larger audience--that of the readers of the Clinical Journal of the American Society of Nephrology. Have fun.

A rare case: childhood-onset C3 glomerulonephritis due to homozygous factor H deficiency

C3 glomerulopathy is a recently described pathological entity including dense deposit disease and C3 glomerulonephritis (C3GN). In some cases, C3 glomerulopathy is associated with defects or even complete deficiency of factor H. However, complete factor H deficiency among patients with C3GN is rare, and paediatric cases have not yet been described. Here, we report a child with homozygous factor H deficiency who presented with haematuria and minor proteinuria, together with undetectable plasma C3 levels, at the age of 10 years. Kidney biopsy demonstrated C3GN. Detailed complement analysis revealed complete factor H deficiency due to a homozygous CFH mutation. Furthermore, there was a complete deletion of CFHR-1/-3. During follow-up, the patient has had recurrent episodes of macro-haematuria and minor proteinuria, but during 4 years of follow-up, no deterioration of renal function has been observed. Mutations of factor H in C3GN have been described; however, complete CFH deficiency is rare in these patients. Furthermore, clinical presentation usually occurs in adulthood. Therefore, this case presents a rare manifestation of the disease and might contribute to the early detection of similar cases also in childhood.

Recent insights into C3 glomerulopathy

‘C3 glomerulopathy’ is a recent disease classification comprising several rare types of glomerulonephritis (GN), including dense deposit disease (DDD), C3 glomerulonephritis (C3GN) and CFHR5 nephropathy. These disorders share the key histological feature of isolated complement C3 deposits in the glomerulus. A common aetiology involving dysregulation of the alternative pathway (AP) of complement has been elucidated in the past decade, with genetic defects and/or autoantibodies able to be identified in a proportion of patients. We review the clinical and histological features of C3 glomerulopathy, relating these to underlying molecular mechanisms. The role of uncontrolled C3 activation in pathogenesis is emphasized, with important lessons from animal models. Methods, advantages and limitations of gene testing in the assessment of individuals or families with C3 glomerulopathy are discussed. While no therapy has yet been shown consistently effective, clinical evaluation of agents targeting specific components of the complement system is ongoing. However, limits to current knowledge regarding the natural history and the appropriate timing and duration of proposed therapies need to be addressed.