C3 Glomerulopathy Masquerading as Acute Postinfectious Glomerulonephritis

Diagnostic Challenges and Emerging Pathogeneses of Selected Glomerulopathies

Recent progress in glomerular immune complex and complement-mediated diseases have refined diagnostic categories and informed mechanistic understanding of disease development in pediatric patients. Herein, we discuss selected advances in 3 categories. First, membranous nephropathy antigens are increasingly utilized to characterize disease in pediatric patients and include phospholipase A2 receptor (PLA2R), Semaphorin 3B (Sema3B), neural epidermal growth factor-like 1 (NELL1), and protocadherin FAT1, as well as the lupus membranous-associated antigens exostosin 1/2 (EXT1/2), neural cell adhesion molecule 1 (NCAM1), and transforming growth factor beta receptor 3 (TGFBR3). Second, we examine advances in techniques for paraffin and light chain immunofluorescence (IF), including the former's function as a salvage technique and their necessity for diagnosis in adolescent cases of membranous-like glomerulopathy with masked IgG kappa deposits (MGMID) and proliferative glomerulonephritis with monotypic Ig deposits (PGNMID), respectively. Finally, progress in understanding the roles of complement in pediatric glomerular disease is reviewed, with specific attention to overlapping clinical, histologic, and genetic or functional alternative complement pathway (AP) abnormalities among C3 glomerulopathy (C3G), infection-related and post-infectious GN, "atypical" post-infectious GN, immune complex mediated membranoproliferative glomerulonephritis (IC-MPGN), and atypical hemolytic uremic syndrome (aHUS).

Evaluation of the significance of complement-related genes mutations in atypical postinfectious glomerulonephritis: a pilot study

BACKGROUND

Postinfectious glomerulonephritis with C3-dominant glomerular deposition (C3-PIGN) involves C3-dominant glomerular deposition without immunoglobulin. Atypical C3-PIGN involves persistent hypocomplementemia. We investigated the clinical features and explored complement-related gene mutations in atypical PIGN patients.

METHODS

We enrolled atypical C3-PIGN patients and collected data regarding the clinical presentation and pathological characteristics and follow-up data. We measured the levels of complement associated antibodies and performed whole-exome sequencing (WES) to detect mutations in complement-related genes.

RESULTS

The analysis included six atypical C3-PIGN patients. All patients were antistreptolysin-O (ASO) positive. All patients had varying degrees of hematuria, and four patients had proteinuria. None of the patients were positive for complement-related antibodies. All patients possessed mutations of genes related to the complement pathway, including alternative complement pathway genes-CFI, CFH, CFHR3, CFHR5; the lectin pathway gene-MASP2; and the common complement pathway gene-C8A. The rare variant of CFHR3 has been reported in C3 glomerulonephritis. During 56-73 months of follow-up, the levels of urine markers in three patients recovered within 6 months, and the remaining patients had abnormal urine test results over 12 months. Patients who received glucocorticoid therapy recovered faster.

CONCLUSIONS

Our study suggested that complement-related gene mutations may be an important cause of persistent hypocomplementemia in atypical C3-PIGN patients. In addition to variations in alternate pathway-related genes, we also found variations in lectin pathway-related genes, especially MASP2 genes. Although the overall prognosis was good, atypical C3-PIGN patients exhibited a longer period for recovery. Our results suggested that atypical C3-PIGN patients should receive more medical attention and need testing for mutations in complement-related genes.

Successful treatment of infectious endocarditis-associated glomerulonephritis during active hepatitis C infection: a case report

BACKGROUND

Hepatitis C virus (HCV) may play a pathogenic role in several forms of immune complex glomerulonephritis (GN). We present a patient whose initial clinical presentation instilled suspicion of HCV-related renal involvement. Yet, histopathologic data oriented towards a different diagnosis.

CASE PRESENTATION

A 68-year old man presented with kidney dysfunction, cryoglobulins, low C4 level, high HCV-RNA and cutaneous vasculitis. The first hypothesis was a hepatitis C-related cryoglobulinemic glomerulonephritis. Renal biopsy revealed endocapillary and mesangial cells hypercellularity with complement C3 and IgM deposits. The echocardiography showed an infectious endocarditis (IE) on aortic valve. Appropriate antibiotic therapy and a prosthetic valve replacement were performed, obtaining recovery of renal function.

CONCLUSION

HCV infection may be linked to multiple renal manifestations, often immune-complex GN such as cryoglobulinemic membrano-proliferative GN. Renal disease due to IE is usually associated to focal, segmental or diffuse proliferative GN, with prominent endocapillary proliferation. The most common infectious agents are Staphylococcus aureus and Streptococcus species. This case report may be relevant because the renal dysfunction was highly suggestive of a cryoglobulinemic GN on a clinical ground, but the histologic pattern after performing the renal biopsy oriented towards a different cause of the underlying disease, that required a specific antibiotic treatment. The renal biopsy is always required to confirm a clinical suspicious in patients affected by multiple comorbidities.

Genetic analysis of CFH and MCP in Egyptian patients with immune-complex proliferative glomerulonephritis

Glomerulonephritis (GN) is a complex disease with intricate underlying pathogenic mechanisms. The possible role of underlying complement dysregulation is not fully elucidated in some GN subsets, especially in the setting of autoimmunity or infection. In the current study, diagnosed cases of lupus nephritis (LN) and post-infectious GN (PIGN) were recruited for molecular genetic analysis and targeted next-generation DNA sequencing was performed for two main complement regulating genes: in the fluid phase; CFH, and on tissue surfaces; MCP. Three heterozygous pathogenic variants in CFH (Q172*, W701*, and W1096*) and one likely pathogenic heterozygous variant in MCP (C223R) have been identified in four of the studied LN cases. Additionally, among the several detected variants of uncertain significance, one novel variant (CFH:F614S) was identified in 74% of the studied LN cases and in 65% of the studied PIGN cases. This variant was detected for the first time in the Egyptian population. These findings suggest that subtle mutations may be present in complement regulating genes in patients with immune-complex mediated category of GN that may add to the disease pathogenesis. These findings also call for further studies to delineate the impact of these gene variants on the protein function, the disease course, and outcome.

Clinical and Pathophysiological Insights Into Immunological Mediated Glomerular Diseases in Childhood

The kidney is often the target of immune system dysregulation in the context of primary or systemic disease. In particular, the glomerulus represents the anatomical entity most frequently involved, generally as the expression of inflammatory cell invasion or circulant or in situ immune-complex deposition. Glomerulonephritis is the most common clinical and pathological manifestation of this involvement. There are no universally accepted classifications for glomerulonephritis. However, recent advances in our understanding of the pathophysiological mechanisms suggest the assessment of immunological features, biomarkers, and genetic analysis. At the same time, more accurate and targeted therapies have been developed. Data on pediatric glomerulonephritis are scarce and often derived from adult studies. In this review, we update the current understanding of the etiologic events and genetic factors involved in the pathogenesis of pediatric immunologically mediated primitive forms of glomerulonephritis, together with the clinical spectrum and prognosis. Possible new therapeutic targets are also briefly discussed.

Complement dysregulation in glomerulonephritis

Glomerulonephritis (GN) refers to a group of renal diseases affecting the glomeruli due to the damage mediated by immunological mechanisms. A large proportion of the disease manifestations are caused by disturbances in the complement system. They can be due to genetic errors, autoimmunity, microbes or abnormal immunoglobulins, like modified IgA or paraproteins. The common denominator in most of the problems is an overactive or misdirected alternative pathway complement activation. An assessment of kidney function, amount of proteinuria and hematuria are crucial elements to evaluate, when glomerulonephritis is suspected. However, the cornerstones of the diagnoses are renal biopsy and careful examination of the complement abnormality. Differential diagnostics between the various forms of GN is not possible based on clinical features, as they may vary greatly. This review describes the known mechanisms of complement dysfunction leading to different forms of primary GN (like IgA glomerulonephritis, dense deposit disease, C3 glomerulonephritis, post-infectious GN, membranous GN) and differences to atypical hemolytic uremic syndrome. It also covers the basic elements of etiology-directed therapy and prognosis of the most common forms of GN. Common principles in the management of GN include treatment of hypertension and reduction of proteinuria, some require immunomodulating treatment. Complement inhibition is an emerging treatment option. A thorough understanding of the basic disease mechanism and a careful follow-up are needed for optimal therapy.

Evolving complexity of complement-related diseases: C3 glomerulopathy and atypical haemolytic uremic syndrome

PURPOSE OF REVIEW

The current review will discuss recent advances in our understanding of the pathology of C3 glomerulopathy and atypical haemolytic uremic syndrome (aHUS).

RECENT FINDINGS

C3 glomerulopathy and aHUS are associated with abnormalities of control of the alternative pathway of complement. Recent articles have provided new insights into the classification of C3 glomerulopathy and its relationship to idiopathic immune complex-mediated glomerulonephritis. They suggest that there may be considerable overlap in pathogenesis between these entities and have indicated novel ways in which classification may be improved. There is increasing evidence that monoclonal gammopathy may cause C3 glomerulopathy or aHUS in older patients and emerging evidence that treatment of the underlying plasma cell clone may ameliorate the kidney disease.

SUMMARY

Recent work has provided new insights into the causes of C3 glomerulopathy and aHUS, and the mechanism by which complement is dysregulated. This is of particular importance with the advent of new therapeutic agents which can specifically target different parts of the complement cascade.

C4 Nephritic Factors in C3 Glomerulopathy: A Case Series

BACKGROUND

C3 glomerulopathy (C3G) defines a group of rare complement-mediated kidney diseases with a shared underlying pathophysiology: dysregulation of complement in the fluid phase and glomerular microenvironment. Dysregulation can be driven by autoantibodies to C3 and C5 convertases.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

168 patients with C3G (dense deposit disease, 68; C3 glumerulonephritis, 100) selected from our C3G biobank.

OUTCOMES

Patient-purified immunoglobulin Gs were tested for C4 nephritic factors (C4NeFs). These autoantibodies recognize C4b2a, the C3 convertase of the classical pathway of complement.

MEASUREMENTS

C4NeFs were detected using a modified hemolytic assay.

RESULTS

C4NeFs were identified in 5 patients, 4 of whom had C3 glomerulonephritis. C4NeFs were associated with dysregulation of C3 and C5 convertases, and they appear to stabilize these convertases in a dose-dependent manner. C4NeFs also appear to protect C4b2a from decay mediated by soluble CR1 and C4 binding protein. The stabilizing activity of the autoantibodies was further demonstrated by using heat treatment to inactivate complement. C4NeFs were not detected in 150 patients with another complement-mediated kidney disease, atypical hemolytic uremic syndrome. They were also absent in 300 apparently healthy controls.

LIMITATIONS

In addition to C4NeFs, 2 patients had positive findings for other autoantibodies: one patient also had autoantibodies to factor H; the other patient also had autoantibodies to C3bBb (C3NeFs).

CONCLUSIONS

The finding of C4NeFs in a small percentage of patients with C3G highlights the challenge in identifying autoantibodies that drive complement dysregulation and underscores the complexity of the autoantibody repertoire that can be identified in these patients.

C3 glomerulopathy

C3 glomerulopathy is a recently defined entity that encompasses a group of kidney diseases caused by abnormal control of complement activation with deposition of complement component C3 in glomeruli leading to variable glomerular inflammation. Before the recognition of the unique pathogenesis of these cases, they were variably classified according to their morphological features. C3 glomerulopathy accounts for roughly 1% of all renal biopsies. Clear definition of this entity has allowed a better understanding of its pathogenesis and clinical course and is likely to lead to the design of rational therapies over the next few years.

Atypical hemolytic uremic syndrome and C3 glomerulopathy: conclusions from a "Kidney Disease: Improving Global Outcomes" (KDIGO) Controversies Conference

In both atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G) complement plays a primary role in disease pathogenesis. Herein we report the outcome of a 2015 Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference where key issues in the management of these 2 diseases were considered by a global panel of experts. Areas addressed included renal pathology, clinical phenotype and assessment, genetic drivers of disease, acquired drivers of disease, and treatment strategies. In order to help guide clinicians who are caring for such patients, recommendations for best treatment strategies were discussed at length, providing the evidence base underpinning current treatment options. Knowledge gaps were identified and a prioritized research agenda was proposed to resolve outstanding controversial issues.

C3 glomerulopathy and current dilemmas

C3 glomerulopathy (C3G) is a recently identified disease entity caused by dysregulation of the alternative complement pathway, and dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) are its components. Because laboratory detection of complement dysregulation is still uncommon in practice, "dominant C3 deposition by two orders greater than that of immunoglobulins in the glomeruli by immunofluorescence", as stated in the consensus report, defines C3G. However, this morphological definition possibly includes the cases with glomerular diseases of different mechanisms such as post-infectious glomerulonephritis. In addition, the differential diagnosis between DDD and C3GN is often difficult because the distinction between these two diseases is based solely on electron microscopic features. Recent molecular and genetic advances provide information to characterize C3G. Some C3G cases are found with genetic abnormalities in complement regulatory factors, but majority of cases seem to be associated with acquired factors that dysregulate the alternative complement pathway. Because clinical courses and prognoses among glomerular diseases with dominant C3 deposition differ, further understanding the background mechanism, particularly complement dysregulation in C3G, is needed. This may resolve current dilemmas in practice and shed light on novel targeted therapies to remedy the dysregulated alternative complement pathway in C3G.

Severe active C3 glomerulonephritis triggered by immune complexes and inactivated after eculizumab therapy

Background

Understanding the role of alternative complement pathway dysregulation in membranoproliferative glomerulonephritis (MPGN) has led to a dramatic shift in its classification into two subgroups: immune complex-mediated MPGN and complement-mediated MPGN, consisting of dense deposit disease and C3 glomerulonephritis (C3GN). A limited number of C3GN cases have been published to date with not yet conclusive results since the novel therapeutic approach with eculizumab was introduced.

Case presentation

We report the clinical follow-up of a 16-year-old patient in whom a diagnosis of C3GN was confirmed by immunofluorescence and electron microscopy in second and third kidney biopsies, while the first biopsy revealed idiopathic immune complex-mediated MPGN type III, Anders and Strife variant, which failed to improve after several attempts at conventional immunosuppression therapy. Although applied late in an already fairly advanced stage of the severe active form of MPGN, the efficacy of eculizumab on C3GN was evidenced clinically and pathohistologically. Its beneficial influence on pathomorphogenesis was demonstrated by a unique follow-up in the last three biopsies, despite the recent observation, confirmed in this study, of eculizumab binding within the kidney tissue.

Conclusions

Clinicians and pathologists should be aware that, in some patients, an underlying genetic or acquired complement alternative pathway abnormality can be masked by an initial immune complex-mediated mechanism, which subsequently triggers an unbalanced excessive continual driving of complement terminal pathway activation and the development of C3GN. In such a patient, supplementary steroids in addition to eculizumab appear necessary to achieve an adequate response.

Protracted Clinical Course of Postinfectious Glomerulonephritis in a Previously Healthy Child

Acute postinfectious glomerulonephritis (PIGN) affects children typically after upper respiratory tract or skin infections with streptococci but can complicate the course of other infections. In children, it is generally a self-limiting disease with excellent prognosis. This paper reports a previously healthy 4-year-old boy who experienced a protracted course of PIGN with persisting episodes of gross haematuria, proteinuria, decreased complement C3c levels but normal P-creatinine levels. Due to the protracted course and the nephrotic-range proteinuria, a renal biopsy was performed 6 months after the initial presentation and the overall pathology was consistent with acute endocapillary glomerulonephritis.

Revisiting post-infectious glomerulonephritis in the emerging era of C3 glomerulopathy

Background

Post-infectious glomerulonephritis (PIGN) is an immune complex-mediated glomerular injury that typically resolves. Dominant C3 deposition is characteristic of PIGN, but with the emergence of C3 glomerulonephritis (C3GN) as a distinct entity, it is unclear how the pathologic similarities between PIGN and C3GN should be reconciled. Therefore, nephrologists and nephropathologists need additional guidance at the time of biopsy.

Methods

We studied 23 pediatric and young adult patients diagnosed with PIGN. Patients were divided into two groups, one with co-dominance between C3 and immunoglobulins and the other meeting proposed diagnostic criteria for C3GN. Clinical and pathological features were compared.

Results

No clinical and/or pathological features could distinguish between those with C3-co-dominant deposits and those with C3 dominance. Nearly all patients in both groups regained their baseline renal function without clinical intervention.

Conclusions

Although the identification of abnormalities of the alternative pathway of complement is characteristic of C3GN, testing is not widely available and the turnaround time often exceeds 1 month. Our study found that PIGN with either co-dominant or dominant C3 deposition in a cohort of young patients has excellent short-term outcomes. Close clinical observation for persistent abnormalities, such as hypocomplementemia, prolonged hematuria or proteinuria, is recommended to single out patients that may harbor intrinsic complement abnormalities.

Kidney Disease Caused by Dysregulation of the Complement Alternative Pathway: An Etiologic Approach

Kidney diseases caused by genetic or acquired dysregulation of the complement alternative pathway (AP) are traditionally classified on the basis of clinical presentation (atypical hemolytic uremic syndrome as thrombotic microangiopathy), biopsy appearance (dense deposit disease and C3 GN), or clinical course (atypical postinfectious GN). Each is characterized by an inappropriate activation of the AP, eventuating in renal damage. The clinical diversity of these disorders highlights important differences in the triggers, the sites and intensity of involvement, and the outcome of the AP dysregulation. Nevertheless, we contend that these diseases should be grouped as disorders of the AP and classified on an etiologic basis. In this review, we define different pathophysiologic categories of AP dysfunction. The precise identification of the underlying abnormality is the key to predict the response to immune suppression, plasma infusion, and complement-inhibitory drugs and the outcome after transplantation. In a patient with presumed dysregulation of the AP, the collaboration of the clinician, the renal pathologist, and the biochemical and genetic laboratory is very much encouraged, because this enables the elucidation of both the underlying pathogenesis and the optimal therapeutic approach.

Histopathology of MPGN and C3 glomerulopathies

'Membranoproliferative' describes glomerular injury characterized by capillary wall thickening and mesangial expansion owing to increased matrix deposition and hypercellularity. The presence of immune deposits is indicative of membranoproliferative glomerulonephritis (MPGN). Historically, MPGN was further classified into three types according to the appearance and site of the electron-dense deposits seen by electron microscopy, but it is now recognized that many cases show only deposition of the complement component C3, owing to abnormal control of the alternative pathway of complement activation-these cases are now classified as C3 glomerulopathies. Not all cases of C3 glomerulopathy, however, show an MPGN pattern. C3 glomerulopathies include dense deposit disease, which shows dense osmiophilic deposits, and C3 glomerulonephritis, which shows isolated deposits. In many cases, the genetic mutations or autoantibodies responsible for C3 deposition have been identified. Some patients in whom complement control is abnormal will accumulate small amounts of immunoglobulin in their glomeruli and so, in everyday practice, the morphological diagnosis of 'glomerulonephritis with dominant C3' is useful for identifying patients who require investigation of the complement pathway. The recognition that many cases of MPGN are C3 glomerulopathies and that the underlying cause can often be identified in immunoglobulin-associated cases means that the diagnosis of idiopathic MPGN is now very uncommon.

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.

Successful treatment of infectious endocarditis associated glomerulonephritis mimicking c3 glomerulonephritis in a case with no previous cardiac disease

We report a 42-year-old man with subacute infectious endocarditis (IE) with septic pulmonary embolism, presenting rapidly progressive glomerulonephritis and positive proteinase 3-anti-neutrophil cytoplasmic antibody (PR3-ANCA). He had no previous history of heart disease. Renal histology revealed diffuse endocapillary proliferative glomerulonephritis with complement 3- (C3-) dominant staining and subendothelial electron dense deposit, mimicking C3 glomerulonephritis. Successful treatment of IE with valve plastic surgery gradually ameliorated hypocomplementemia and renal failure; thus C3 glomerulonephritis-like lesion in this case was classified as postinfectious glomerulonephritis. IE associated glomerulonephritis is relatively rare, especially in cases with no previous history of valvular disease of the heart like our case. This case also reemphasizes the broad differential diagnosis of renal involvement in IE.

Successful management of a patient with a C3 Glomerulonephritis and crescentic pattern: a case report

BACKGROUND

Crescentic glomerulonephritis is a rare condition in children and is typically associated with renal insufficiency. Dysfunction of the alternative complement pathway is an unusual aetiology with an unknown mechanism.

CASE PRESENTATION

We report a case of a previously healthy 12-year-old Caucasian girl who was examined on emergency owing to an asymptomatic gross haematuria. An active urinary sediment and nephrotic-range proteinuria were identified, and serologic examination showed a decreased serum C3 concentration not associated with any immunologic or infectious cause. Oedema, hypertension, and renal insufficiency were not observed. A renal biopsy was performed, and crescentic glomerulonephritis associated with C3 glomerulonephritis was diagnosed. Prompt treatment with intravenous steroids resulted in complete resolution of the gross haematuria. Further examination did not detect any underlying acquired cause. A combination of oral steroids and cyclophosphamide, followed by mycophenolate mofetil, was maintained and resulted in clinical remission during an 8-month follow-up.

CONCLUSION

The presence of severe injury such as crescentic glomerulonephritis secondary to C3 glomerulonephritis is extremely unusual in children. This is the first known case of paediatric crescentic glomerulonephritis secondary to C3 glomerulonephritis that presented with gross haematuria and was treated early and effectively with immunosuppressive therapy based on its severe histologic features.

Bartonella henselae endocarditis and glomerulonephritis with dominant C3 deposition in a 21-year-old male with a Melody transcatheter pulmonary valve: case report and review of the literature

We report a case of a 21-year-old young man with underlying congenital heart disease who developed Bartonella henselae endocarditis of the right ventricular outflow tract (RVOT) conduit of his Melody transcatheter (percutaneous) pulmonary valve (TPV), with an initial presentation of glomerulonephritis with a dominant C3 pattern, with renal failure and circulating cryoglobulins. There are few reports of a glomerulonephritis with a dominant C3 pattern presenting as a manifestation of B. henselae endocarditis. While most cases of B. henselae endocarditis affect the aortic valve, in this case the valve damage was to the RVOT of the Melody TPV, a percutaneous transcatheter valve delivery system that had previously replaced his pulmonary homograft, which had become dysfunctional as a result of prior Streptococcus viridans endocarditis. The pulmonary homograft had been in place since childhood as a result of a Ross procedure to repair his congenital aortic stenosis. The patient's renal failure significantly improved after surgical resection of the infected RVOT and institution of appropriate antibiotic therapy.

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.

Evolution of immunoglobulin deposition in C3-dominant membranoproliferative glomerulopathy

BACKGROUND

Complement 3 glomerulopathy (C3GN) is a newly proposed subcategory of glomerular disease with features including membranoproliferative glomerulonephritis (MPGN), C3-dominant immunofluorescent staining without appreciable immunoglobulin deposition, and electron-dense deposits. Aberrations of alternative complement pathway (AP) have been found in many C3GN patients.

CASE-DIAGNOSIS/TREATMENT

A 13-year-old boy presented with edema in association with an upper respiratory infection. Studies demonstrated nephrotic syndrome with hematuria and markedly low C3 and C4. Initial renal biopsy showed MPGN with strong C3 and immunoglobulin deposition. The patient partially responded to immunosuppression. Follow-up biopsies at 10 months and 3 years demonstrated MPGN with strong C3, with little to no immunoglobulin deposition. Based on this and elevated SC5b-9, treatment was changed to eculizumab with further decrease in proteinuria.

CONCLUSIONS

Serial biopsies illustrated marked variability in immunoglobulin deposition in MPGN with persistently strong C3 deposition. Whether this evolution was related to the course of disease or to therapeutic intervention, the pathologic progression documented in this series of biopsies challenges the newly proposed subcategories of MPGN.

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.

Toward a working definition of C3 glomerulopathy by immunofluorescence

Precise immunofluorescence criteria for C3 glomerulopathy remain to be defined. Here we tested hierarchical immunofluorescence criteria with varying stringency for C3 glomerulopathy in a cohort with dense deposit disease as the gold standard and then applied these criteria to analyze the incidence of C3 glomerulopathy in membranoproliferative glomerulonephritis (MPGN) types 1 and 3. Among 319 archived cases of primary MPGN types 1-3, immunofluorescence reports were retrospectively coded as glomerular deposits of the following: C3 only; C3 dominant with trace or 1+ immunoglobulin (Ig)M only; and C3 dominant and at least two orders of intensity stronger than any combination of IgG, IgM, IgA, and C1q. The most restrictive criteria of 'C3 only' captured only half of the cases with dense deposit disease (compared with 8% of type 1 and 10% of type 3). Adding the most liberal definition identified 88% of those with dense deposit disease (compared with 31% of type 1 and 39% of type 3). The unaccounted 12% had stronger intensity of Ig staining, but it never exceeded the intensity of C3. Among MPGN type 3, 90% of C3 glomerulopathy cases were the Strife and Anders variant. Repeat biopsies in C3 glomerulopathy revealed a change in immunofluorescence pattern in 10 of 23 biopsies. The prevalence of low serum C3 and/or low C4 did not significantly differ among the three immunofluorescence criteria. Thus, 'C3 only' is an impractical definition of C3 glomerulopathy, and we propose a definition of C3 dominant and at least two orders of magnitude more intense than any other immune reactant, which requires validation by alternative pathway evaluation. These criteria provide a framework for identifying patients most likely to benefit from investigations of alternative complement pathway dysregulation.

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.

Pathogenesis of the C3 glomerulopathies and reclassification of MPGN

Until recently, membranoproliferative glomerulonephritis (MPGN) was clinically classified as either primary, idiopathic MPGN or as secondary MPGN when an underlying aetiology was identifiable. Primary MPGN was further classified into three types--type I, type II, and type III--based principally on the ultrastructural appearance and location of electron-dense deposits. Both the clinical and histopathologic schemes presented problems, however, as neither was based on disease pathogenesis. An improved understanding of the role of complement in the pathogenesis of MPGN has led to a proposed reclassification into immunoglobulin-mediated disease (driven by the classical complement pathway) and non-immunoglobulin-mediated disease (driven by the alternative complement pathway). This reclassification has led to improved diagnostic clinical algorithms and the emergence of a new grouping of diseases known as the C3 glomerulopathies, best represented by dense deposit disease and C3 glomerulonephritis. In this Review, we re-examine the previous and current classification schemes of MPGN, focusing on the role of complement. We survey current data about the pathogenesis of the C3 glomerulopathies, including familial studies and patient cohorts from the USA and Europe. In addition, we discuss the diagnosis, treatment, and prognosis of the C3 glomerulopathies.