Histopathology of MPGN and C3 glomerulopathies

Pediatric Immunodeficiency Caused by Complement Classical and Alternative Pathway Defects Due to a Homozygous CFI Variant: A Case Report

Complement factor I (CFI) deficiency is a rare primary immunodeficiency that disrupts the classical and alternative complement pathways, potentially causing severe recurrent infections and autoimmune manifestations in pediatric patients. However, the coexistence of both pathways in a pediatric patient is extremely uncommon. We report a seven-year-old patient with a rare primary immunodeficiency disorder who presented with recurrent middle ear infections, paronychia, gastrointestinal infections, and respiratory infections. Genetic testing revealed a previously unreported homozygous variant in the CFI gene (c.848A>G; p.D283G). Immunological testing showed a decrease in complement C3, CFI, and CFH levels in the patient. Interestingly, the patient presented with IgA vasculitis, with renal pathology showing deposits of immune complexes containing IgA, IgG, IgM, and C1q. By considering the child's condition and genetic test results, the child was treated symptomatically and received regular peritoneal dialysis treatment. Subsequently, the child's condition improved compared to before and was discharged from the hospital. This case highlights the importance of considering CFI deficiency in children with recurrent infections and abnormalities in both the classical and alternative complement pathways. Our findings expand the known phenotypic spectrum of CFI deficiency and contribute to understanding genotype-phenotype correlations in complement disorders.

Autoantibodies Against Factor B and Factor H Without Pathogenic Effects in a Patient with Immune Complex-Mediated Membranoproliferative Glomerulonephritis

Background: Membranoproliferative glomerulonephritis (MPGN) is an umbrella term for chronic disorders affecting the glomeruli. MPGN is often accompanied by the presence of autoantibodies against complement components. However, the actual pathogenic effects of such autoantibodies, if any, are rarely studied. In this work, we investigated the role of anti-complement autoantibodies in an IC-MPGN patient. Methods: The presence of autoantibodies, their binding site, isotype, and titer were analyzed in ELISA. Antibody-antigen complexes were detected in the patient's serum using Western blot. Autoantibodies were studied in functional assays to analyze their effects on C3 convertase, complement deposition, cofactor activity, C3b binding, and hemolysis. Results: We identified autoantibodies against factor B (FB) and factor H (FH) in the patient's serum. Both FB-, and FH-autoantibodies were of IgG2, IgG3, IgG4, and IgGκ, IgGλ isotypes. FB-autoantibodies bound to the Ba and the enzymatically active Bb part of FB. FH-autoantibodies bound to the N- and C-termini of FH and cross-reacted with FHL-1 and FHR-1 proteins. In vivo formed complexes of the autoantibodies with both FB and FH were detected in the IgG fraction isolated from the serum. The autoantibodies did not influence solid-phase C3 convertase assembly and its FH-mediated decay. The free autoantibodies had no effect on complement deposition and on FH cofactor activity but slightly reduced C3b binding to FH. The IgG fraction of the patient dose-dependently inhibited complement-mediated rabbit red blood cell lysis, and the free autoantibodies decreased the solid phase C3 convertase activity. Conclusions: This case highlights that FB- and FH-autoantibodies are not necessarily pathogenic in IC-MPGN.

Challenges in the Diagnosis and Management of Immune Complex-Mediated Membranoproliferative Glomerulonephritis and Complement 3 Glomerulopathy

Immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) and complement 3 glomerulopathy (C3G) are rare, complement-mediated kidney diseases, previously classified under the group of kidney disorders termed membranoproliferative glomerulonephritis (MPGN) type 1, type 2, and type 3. Despite new advances in our understanding of IC-MPGN and C3G, several unmet needs persist in the diagnosis and management of patients with these nephropathies, due in part to their rarity and their overlapping clinical presentations, histologic features, and underlying pathophysiologies. This review summarizes our current understanding of the role of complement in IC-MPGN and C3G, and underlines the key histopathologic differences between the diseases. Using seven illustrative patient cases, we discuss consensus guideline treatment recommendations and the uncertainties, challenges, and considerations regarding the diagnosis and management of patients with IC-MPGN and C3G in clinical practice. The presented cases emphasize the need for a multidisciplinary approach encompassing primary care providers (PCPs), nephrologists, nephropathologists, and laboratory scientists. Key knowledge gaps are evaluated, including differential diagnoses, underlying pathologic mechanisms, and the lack of effective treatments targeting drivers of disease. As the therapeutic landscape evolves, an improved understanding of IC-MPGN and C3G is crucial to identifying optimal targeted-treatment strategies and facilitating a personalized approach to the management of these complex glomerular diseases.

Repeated Kidney Biopsy in Membranoproliferative Glomerulonephritis

Introduction

Membranoproliferative glomerulonephritis (MPGN) is a heterogeneous pattern of glomerular injury. Repeated kidney biopsies may elucidate pathogenic mechanisms and guide diagnostic strategies.

Methods

We included 82 patients diagnosed with MPGN by kidney biopsy who underwent at least two biopsies between 1997 and 2023 at Peking University First Hospital. Clinical and pathological data were analyzed retrospectively.

Results

Of 342 MPGN patients, 95 (28%) had repeated biopsies (0.9-4.0 years apart). This incidence was higher than in other glomerulonephropathies under immunosuppression. Among the 82 patients analyzed (excluding kidney transplants and ≤3-month biopsy intervals), 42 were initially diagnosed with non-MPGN pathology. At the second biopsy, proteinuria increased (from 2.9 to 6.3 g/day), eGFR declined (from 76 to 47 mL/min/1.73 m2), and renal C3 deposition was stronger (p = 0.04). Thirty patients (37%) had etiological reclassification, mostly to monoclonal gammopathy of renal significance (MGRS). Compared to idiopathic MPGN, MGRS patients were older (53 vs. 35 years) and had worse renal function (eGFR 57 vs. 81 mL/min/1.73 m2) but slower eGFR decline (-7 vs. -12 mL/min/1.73 m2/year). Most MGRS patients (64%) remained negative for monoclonal protein in serum or urine immunofixation, necessitating repeat biopsy and clone-directed therapy.

Conclusion

In this study, about half and one-third of patients underwent morphological and etiological reclassification, respectively. Stronger complement deposition may drive morphological changes. Repeated kidney biopsies are crucial for diagnosing MGRS, especially in patients with negative immunofixation.

Glomerular injury induced by vinyl carbamate in A/J inbred mice: a novel model of membranoproliferative glomerulonephritis

Ethyl carbamate (EC) is a process contaminant found in fermented foods and alcoholic beverages. Metabolic conversion of ethyl carbamate generates vinyl carbamate (VC), a carcinogenic metabolite. EC, as a Group 2A probable human carcinogen, and the more potent VC, are known to cause tumors in rodents. However, their effects on the kidney are unknown and were explored here. Female A/J inbred mice received an intraperitoneal injection of vehicle or VC. Beginning 5 weeks after VC injection, mice showed signs of moribund state. Mouse necropsies revealed renal glomerular injury that histopathologically recapitulated human membranoproliferative glomerulonephritis (MPGN), as evidenced by light microscopy, immunostaining for immunoglobulins and complements, and electron microscopy. To determine the molecular pathomechanisms, a post-hoc analysis was performed on a publicly available RNA-Seq transcriptome of kidneys from control rats and rats treated with fermented wine containing high concentrations of EC. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses of the differentially expressed genes revealed that the complement and coagulation cascades were a top predicted biological process involved. Furthermore, pathway-based data integration and visualization revealed that key regulators of complement activation were altered by high EC treatment. Among these, complement factors (CF) D and H, critical positive and negative regulators of the alternative pathway, respectively, were most affected, with CFD induced by 3.49-fold and CFH repressed by 5.9-fold, underscoring a hyperactive alternative pathway. Consistently, exposure of primary glomerular endothelial cells to EC or VC resulted in induction of CFD and repression of CFH, accompanied by increased fixation of C3 and C5b9. This effect seems to be mediated by Ras, one of the top genes that interact with both EC and VC, as identified by analyzing the chemical-gene/protein interactions database. Indeed, EC or VC-elicited complement activation was associated with activation of Ras signaling, but was abolished by the Ras inhibitor farnesyl thiosalicylic acid. Collectively, our findings suggest that VC, a metabolite of EC, induces glomerular injury in mice akin to human MPGN, possibly via perturbing the expression of complement regulators, resulting in an effect that favors activation of the alternative complement pathway.

A compared histopathological study on kidneys and eye bulbs in distinct clinical presentations of canine leishmaniasis by Leishmania infantum

Canine leishmaniasis (CanL) caused by Leishmania infantum commonly progresses with renal and ophthalmic lesions associated with active systemic disease. As chronic inflammation related to immune complex deposits is a pathophysiological factor in the development of both glomerulonephritis and uveitis, we aimed to evaluate renal and ocular histopathological lesions and analyze whether they were related to each other and the clinical degree of the disease. For that, we evaluated 15 dogs from CanL-endemic areas. L. infantum PCR-positive dogs were studied according to disease severity into two different groups: Group-1 (G1) had data from seven dogs with mild to moderate CanL and no history of treatment, and G2 was formed with eight dogs with severe to terminal disease that had not responded to CanL treatment. Histopathological analysis of kidneys showed higher frequencies and intensities of glomerular basement membrane thickening (p = 0.026), deposits in glomeruli (p = 0.016), epithelial necrosis (p = 0.020), tubular dilatation (p = 0.003) and interstitial fibrosis (p = 0.04) in G2 dogs than in G1 dogs. Surprisingly, the histopathology of eye bulbs showed a higher frequency and intensity of retinitis (p = 0.019) in G1 dogs than in G2 dogs. The comparative analysis showed that there was no correspondence between histopathological findings in kidneys versus eyes in milder or more severe CanL. Our findings suggested that (1) clinically undetectable eye alterations can be more precocious than those in kidneys in the development of CanL, and (2) the lower frequency of eye lesions and higher frequency of renal lesions in dogs with terminal disease even after treatment indicate that therapy may have been effective in reducing CanL-associated ophthalmic disease but not proportionally in reducing kidney disease.

Unsupervised Clustering of Membranoproliferative Glomerulonephritis and C3 Glomerulopathy Patients Discovers Distinct Patient Groups unlike the Current Classification

INTRODUCTION

Membranoproliferative glomerulonephritis is currently divided into immunoglobulin-mediated glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G); however, the patients often overlap with histology, complement, clinical and prognostic factors. Our aim was to investigate if an unsupervised clustering method finds different patient groups in 44 IC-MPGN/C3G patients using only histological and clinical data available in everyday clinical work.

METHODS

Primary IC-MPGN/C3G adult patients were included whose diagnostic (baseline) native biopsy was obtained in 2006-2017. The biopsies were reassessed and the clinical data at baseline and during follow-up were obtained from the medical records. There were 39 baseline histological and clinical variables included in the unsupervised clustering. Follow-up information was combined with the clustering results.

RESULTS

The clustering resulted in two clusters (n = 24 and n = 20 patients for clusters 1-2, respectively), where cluster 1 had a significantly higher baseline plasma creatinine (mean 213 vs. 104, respectively, p value <0.001) and a lower baseline eGFR than cluster 2 (mean 37 vs. 70, respectively, p value <0.001). Regarding histology, chronic changes such as lobulated glomeruli, mesangial matrix expansion, and glomeruli double contours were more prevalent in cluster 1 (p value <0.001). Biopsy morphology was more often crescentic and membranoproliferative in cluster 1 (p value <0.001). Although the differences were insignificant, cluster 1 patients were in dialysis in the last follow-up or had a progressive disease more often than cluster 2 patients (21% vs. 5%, 38% vs. 10%).

CONCLUSIONS

Our results indicate that these patients share greater similarity than the current classification IC-MPGN versus C3G indicates.

Immunofluorescence Use and Techniques in Glomerular Diseases: A Review

Background

Immunofluorescence (IF) studies play an essential role in the evaluation of medical renal biopsies. Particularly, in the study of renal glomerular diseases, where it provides fundamental data for the diagnosis, classification, and etiology of the glomerular pathologies. Diverse techniques may be used to optimize the utilization of IF studies, from variations on the test methodologies to expertise on the interpretation of the results and knowledge of potential pitfalls.

Summary

This manuscript presents a brief review on the history of IF and its utilization in kidney pathology, followed by a description of the IF methods, including the use of IF on paraffin-embedded tissue (paraffin IF), and other novel techniques. Guidelines on how to best report IF findings are reviewed, along with a description of antibodies commonly used in glomerular diseases, highlighting their distribution within the normal kidney and potential pitfalls in interpretation. Finally, the use and interpretation of IF are discussed in more detail in individual entities on a range of glomerular diseases.

Key Messages

IF is crucial for interpretation of renal biopsies and diagnosis of glomerular diseases. Knowledge of IF techniques, alternative procedures, its use and proper interpretation is essential for optimal utilization of IF in renal pathology, and this review proposes to serve as a simplified and practical guide on this topic.

Iptacopan in Idiopathic Immune Complex-Mediated Membranoproliferative Glomerulonephritis: Protocol of the APPARENT Multicenter, Randomized Phase 3 Study

Introduction

Immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) is an ultra-rare, fast-progressing kidney disease that may be idiopathic (primary) or secondary to chronic infection, autoimmune disorders, or monoclonal gammopathies. Dysregulation of the alternative complement pathway is implicated in the pathophysiology of IC-MPGN; and currently, there are no approved targeted treatments. Iptacopan is an oral, highly potent proximal complement inhibitor that specifically binds to factor B and inhibits the alternative pathway (AP).

Methods

This randomized, double-blind, placebo-controlled phase 3 study (APPARENT; NCT05755386) will evaluate the efficacy and safety of iptacopan in patients with idiopathic (primary) IC-MPGN, enrolling up to 68 patients (minimum of 10 adolescents) aged 12 to 60 years with biopsy-confirmed IC-MPGN, proteinuria ≥1 g/g, and estimated glomerular filtration rate (eGFR) ≥30 ml/min per 1.73 m2. All patients will receive maximally tolerated angiotensin-converting enzyme inhibitor/angiotensin receptor blocker and vaccination against encapsulated bacteria. Patients with any organ transplant, progressive crescentic glomerulonephritis, or kidney biopsy with >50% interstitial fibrosis/tubular atrophy, will be excluded. Patients will be randomized 1:1 to receive either iptacopan 200 mg twice daily (bid) or placebo for 6 months, followed by open-label treatment with iptacopan 200 mg bid for all patients for 6 months. The primary objective of the study is to evaluate the efficacy of iptacopan versus placebo in proteinuria reduction measured as urine protein-to-creatinine ratio (UPCR) (24-h urine) at 6 months. Key secondary end points will assess kidney function measured by eGFR, patients who achieve a proteinuria-eGFR composite end point, and patient-reported fatigue.

Conclusion

This study will provide evidence toward the efficacy and safety of iptacopan in idiopathic (primary) IC-MPGN.

Adjustment of p-value expression to ontology using machine learning for genetic prediction, prioritization, interaction, and its validation in glomerular disease

The results of gene expression analysis based on p-value can be extracted and sorted by their absolute statistical significance and then applied to multiple similarity scores of their gene ontology (GO) terms to promote the combination and adjustment of these scores as essential predictive tasks for understanding biological/clinical pathways. The latter allows the possibility to assess whether certain aspects of gene function may be associated with other varieties of genes, to evaluate regulation, and to link them into networks that prioritize candidate genes for classification by applying machine learning techniques. We then detect significant genetic interactions based on our algorithm to validate the results. Finally, based on specifically selected tissues according to their normalized gene expression and frequencies of occurrence from their different biological and clinical inputs, a reported classification of genes under the subject category has validated the abstract (glomerular diseases) as a case study.

Membranoproliferative glomerulonephritis: no longer the same disease and may need very different treatment

Membranoproliferative glomerulonephritis (MPGN) is a pattern of glomerular injury that may be primary or secondary to infections, autoimmune diseases and haematological disorders. Primary C3G and IC-MPGN are rare and the prognosis is unfavourable. Based on immunofluorescence findings, MPGN has been classified into complement-mediated C3 glomerulopathy (C3G) and immune complex-mediated MPGN (IC-MPGN). However, this classification leaves a number of issues unresolved. The finding of genetic and acquired complement abnormalities in both C3G and IC-MPGN indicates that they represent a heterogeneous spectrum rather than distinct diseases. An unsupervised hierarchical clustering in a cohort of patients with primary C3G and IC-MPGN identified four distinct pathogenetic patterns, characterized by specific histologic and clinical features, and genetic and acquired complement abnormalities. These results provide the groundwork for a more accurate diagnosis and the development of targeted therapies. The drugs that are currently used, such as corticosteroids and immunosuppressants, are frequently ineffective in primary C3G and IC-MPGN. Eculizumab, an anti-C5 monoclonal antibody, has been used occasionally in single cases or small series. However, only a few patients have achieved remission. This heterogeneous response could be related to the extent of terminal complement activation, which may vary substantially from patient to patient. Several drugs that target the complement system at different levels are under investigation for C3G and IC-MPGN. However, clinical trials to test new therapeutics will be challenging and heavily influenced by the heterogeneity of these diseases. This creates the need to characterize each patient to match the specific complement abnormality with the type of intervention.

Kidney diseases

Dysregulation and accelerated activation of the alternative pathway (AP) of complement is known to cause or accentuate several pathologic conditions in which kidney injury leads to the appearance of hematuria and proteinuria and ultimately to the development of chronic renal failure. Multiple genetic and acquired defects involving plasma- and membrane-associated proteins are probably necessary to impair the protection of host tissues and to confer a significant predisposition to AP-mediated kidney diseases. This review aims to explore how our current understanding will make it possible to identify the mechanisms that underlie AP-mediated kidney diseases and to discuss the available clinical evidence that supports complement-directed therapies. Although the value of limiting uncontrolled complement activation has long been recognized, incorporating complement-targeted treatments into clinical use has proved challenging. Availability of anti-complement therapy has dramatically transformed the outcome of atypical hemolytic uremic syndrome, one of the most severe kidney diseases. Innovative drugs that directly counteract AP dysregulation have also opened new perspectives for the management of other kidney diseases in which complement activation is involved. However, gained experience indicates that the choice of drug should be tailored to each patient's characteristics, including clinical, histologic, genetic, and biochemical parameters. Successfully treating patients requires further research in the field and close collaboration between clinicians and researchers who have special expertise in the complement system.

Physiology and pathology of the C3 amplification cycle: A retrospective

The C3 "Tickover" hypothesis, a mechanism whereby the host maintains constant surveillance of potential invading pathogens, targeting them for elimination through amplified C3b generation and C3-dependent effector mechanisms, was proposed by the late Professor Peter Lachmann in 1973. This unique insight came from a combined understanding of the complement system as it was then defined and the nature of the disease process in rare complement deficiencies and complement-driven diseases. In this review, I give a personal perspective of how understanding of "Tickover" has developed in the subsequent 50 years, culminating in the introduction into the clinic of therapeutic agents designed to combat amplification-driven disease.

Overview on the role of complement-specific autoantibodies in diseases

The complement system is recognized as a major pathogenic or contributing factor in an ever-growing number of diseases. In addition to inherited factors, autoantibodies to complement proteins have been detected in various systemic and organ-specific disorders. These include antibodies directed against complement components, regulators and receptors, but also protein complexes such as autoantibodies against complement convertases. In some cases, the autoantibodies are relatively well characterized and a pathogenic role is incurred and their detection has diagnostic value. In other cases, the relevance of the autoantibodies is rather unclear. This review summarizes what we know of complement specific autoantibodies in diseases and identifies unresolved questions regarding their functional effect and relevance.

Association of Histologic Parameters with Outcome in C3 Glomerulopathy and Idiopathic Immunoglobulin-Associated Membranoproliferative Glomerulonephritis

BACKGROUND AND OBJECTIVES

C3 glomerulopathy and idiopathic Ig-associated membranoproliferative GN are kidney diseases characterized by abnormal glomerular complement C3 deposition. These conditions are heterogeneous in outcome, but approximately 50% of patients develop kidney failure within 10 years.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

To improve identification of patients with poor prognosis, we performed a detailed analysis of percutaneous kidney biopsies in a large cohort of patients. Using a validated histologic scoring system, we analyzed 156 native diagnostic kidney biopsies from a retrospective cohort of 123 patients with C3 glomerulopathy and 33 patients with Ig-associated membranoproliferative GN. We used linear regression, survival analysis, and Cox proportional hazards models to assess the relationship between histologic and clinical parameters with outcome.

RESULTS

Frequent biopsy features were mesangial expansion and hypercellularity, glomerular basement membrane double contours, and endocapillary hypercellularity. Multivariable analysis showed negative associations between eGFR and crescents, interstitial inflammation, and interstitial fibrosis/tubular atrophy. Proteinuria positively associated with endocapillary hypercellularity and glomerular basement membrane double contours. Analysis of second native biopsies did not demonstrate associations between immunosuppression treatment and improvement in histology. Using a composite outcome, risk of progression to kidney failure associated with eGFR and proteinuria at the time of biopsy, cellular/fibrocellular crescents, segmental sclerosis, and interstitial fibrosis/tubular atrophy scores.

CONCLUSIONS

Our detailed assessment of kidney biopsy data indicated that cellular/fibrocellular crescents and interstitial fibrosis/tubular atrophy scores were significant determinants of deterioration in kidney function.

Glomerulonefrite membranoproliferativa: classificação histopatológica atual, perfil clínico e desfechos renais

Resumo Introdução: Glomerulonefrite membranoproliferativa (GNMP) é uma doença glomerular rara com prognóstico variável. Recentemente, foi proposta uma nova classificação baseada na presença ou ausência de imunoglobulinas e depósitos de complemento na microscopia de imunofluorescência (IF) da biópsia renal. Os objetivos do estudo foram determinar e comparar as características clínicas, laboratoriais e histopatológicas daqueles com GNMP primária ou secundária, reclassificar as primárias com base em achados da IF e avaliar os desfechos renais. Métodos: Este foi um estudo de coorte observacional retrospectivo realizado em centro único (UNIFESP), com base nos dados coletados de prontuários de pacientes acompanhados de 1996 a 2019. Resultados: Dos 53 casos de GNMP, 36 (67,9%) foram classificados como GNMP primária e 17 (32,1%) como GNMP secundária. A maioria dos pacientes era hipertensa (84,9%) e apresentava edema (88,7%) e anemia (84,9%); 33 (91,7%) pacientes classificados como GNMP primária foram reclassificados como mediados por imunocomplexo e 3 (8,3%) como mediados por complemento. O grupo de GNMP secundária apresentou mais frequentemente hematúria (p <0,001) e maior prevalência de depósitos de IgG (p = 0,02) e C1q (p = 0,003). Com relação ao desfecho, 39% dos pacientes alcançaram remissão parcial ou completa. Albumina sérica inicial mais baixa e proteinúria de 24 horas inicial mais elevada foram fatores associados a pior prognóstico renal. Conclusões: De acordo com a nova classificação histológica, a grande maioria dos casos de GNMP foram classificados como sendo mediados por imunocomplexos. Houve poucas diferenças entre GNMP primária e secundária em relação às suas características clínicas e laboratoriais.

Vascular Occlusion in Kidney Biopsy Is Characteristic of Clinically Manifesting Thrombotic Microangiopathy

Thrombotic microangiopathy (TMA) can sometimes manifest only histologically. Our aim was to retrospectively compare biopsy-proven adult TMA patients showing only histological (h-TMA) or both histological and clinical (c-TMA) TMA in 2006–2017. All native kidney biopsies with TMA were included. Biopsies were re-evaluated by light and electron microscopy, and immunofluorescence. Clinical characteristics, laboratory variables, and treatments were recorded from the electronic medical database. Patients were categorized into h-TMA and c-TMA and these groups were compared. In total, 30 biopsy-proven cases among 7943 kidney biopsies were identified and, of these, 15 had h-TMA and 15 c-TMA. Mean follow-up was 6.3 y, and 73.3% had secondary hemolytic uremic syndrome (HUS) and the rest were atypical HUS. Patient characteristics, treatments, and kidney, and patient survival in the groups were similar. Statistically significant differences were found in histological variables. Vascular myxoid swelling and vascular onion-skinning were almost exclusively detected in c-TMA and, thus, vascular occlusive changes indicate clinically apparent rather than merely histological TMA. In addition, regardless of clinical presentation, kidney and patient survival times were similar in the patient groups highlighting the importance of a kidney biopsy in the case of any kidney-related symptoms.

WT1 complete gonadal dysgenesis with membranoproliferative glomerulonephritis: case series and literature review

BACKGROUND

Intronic WT1 mutations are usually causative of Frasier syndrome with focal segmental glomerulosclerosis as the characteristic nephropathy. Membranoproliferative glomerulonephritis is not commonly associated with disorders of sex development but has been recently identified as a WT1-associated nephropathy, but usually in cases of exonic mutations in either isolated Wilms tumor or Denys-Drash syndrome.

METHODS

The clinical and genetic data from 3 individuals are reported.

RESULTS

This report describes the kidney manifestations in 3 individuals from 2 unrelated families with Frasier syndrome intronic WT1 mutations, noting that 2 of the 3 individuals have histologically confirmed membranoproliferative glomerulonephritis.

CONCLUSIONS

These case reports support expansion of the clinical spectrum of the kidney phenotypes associated with Frasier syndrome providing evidence of an association between WT1 mutation and an immune complex-related membranoproliferative glomerulonephritis. A higher resolution version of the Graphical abstract is available as Supplementary information.

Gain-of-Function Mutations R249C and S250C in Complement C2 Protein Increase C3 Deposition in the Presence of C-Reactive Protein

The impairment of the alternative complement pathway contributes to rare kidney diseases such as atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy (C3G). We recently described an aHUS patient carrying an exceptional gain-of-function (GoF) mutation (S250C) in the classical complement pathway component C2 leading to the formation of hyperactive classical convertases. We now report the identification of the same mutation and another C2 GoF mutation R249C in two other patients with a glomerulopathy of uncertain etiology. Both mutations stabilize the classical C3 convertases by a similar mechanism. The presence of R249C and S250C variants in serum increases complement-dependent cytotoxicity (CDC) in antibody-sensitized human cells and elevates deposition of C3 on ELISA plates coated with C-reactive protein (CRP), as well as on the surface of glomerular endothelial cells. Our data justify the inclusion of classical pathway genes in the genetic analysis of patients suspected of complement-driven renal disorders. Also, we point out CRP as a potential antibody-independent trigger capable of driving excessive complement activation in carriers of the GoF mutations in complement C2.

C3 Glomerulopathy and Related Disorders in Children: Etiology-Phenotype Correlation and Outcomes

BACKGROUND AND OBJECTIVES

Membranoproliferative GN and C3 glomerulopathy are rare and overlapping disorders associated with dysregulation of the alternative complement pathway. Specific etiologic data for pediatric membranoproliferative GN/C3 glomerulopathy are lacking, and outcome data are based on retrospective studies without etiologic data.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A total of 80 prevalent pediatric patients with membranoproliferative GN/C3 glomerulopathy underwent detailed phenotyping and long-term follow-up within the National Registry of Rare Kidney Diseases (RaDaR). Risk factors for kidney survival were determined using a Cox proportional hazards model. Kidney and transplant graft survival was determined using the Kaplan-Meier method.

RESULTS

Central histology review determined 39 patients with C3 glomerulopathy, 31 with immune-complex membranoproliferative GN, and ten with immune-complex GN. Patients were aged 2-15 (median, 9; interquartile range, 7-11) years. Median complement C3 and C4 levels were 0.31 g/L and 0.14 g/L, respectively; acquired (anticomplement autoantibodies) or genetic alternative pathway abnormalities were detected in 46% and 9% of patients, respectively, across all groups, including those with immune-complex GN. Median follow-up was 5.18 (interquartile range, 2.13-8.08) years. Eleven patients (14%) progressed to kidney failure, with nine transplants performed in eight patients, two of which failed due to recurrent disease. Presence of >50% crescents on the initial biopsy specimen was the sole variable associated with kidney failure in multivariable analysis (hazard ratio, 6.2; 95% confidence interval, 1.05 to 36.6; P<0.05). Three distinct C3 glomerulopathy prognostic groups were identified according to presenting eGFR and >50% crescents on the initial biopsy specimen.

CONCLUSIONS

Crescentic disease was a key risk factor associated with kidney failure in a national cohort of pediatric patients with membranoproliferative GN/C3 glomerulopathy and immune-complex GN. Presenting eGFR and crescentic disease help define prognostic groups in pediatric C3 glomerulopathy. Acquired abnormalities of the alternative pathway were commonly identified but not a risk factor for kidney failure.

Genetic testing in the diagnosis of chronic kidney disease: recommendations for clinical practice

The overall diagnostic yield of massively parallel sequencing–based tests in patients with chronic kidney disease (CKD) is 30% for paediatric cases and 6–30% for adult cases. These figures should encourage nephrologists to frequently use genetic testing as a diagnostic means for their patients. However, in reality, several barriers appear to hinder the implementation of massively parallel sequencing–based diagnostics in routine clinical practice. In this article we aim to support the nephrologist to overcome these barriers. After a detailed discussion of the general items that are important to genetic testing in nephrology, namely genetic testing modalities and their indications, clinical information needed for high-quality interpretation of genetic tests, the clinical benefit of genetic testing and genetic counselling, we describe each of these items more specifically for the different groups of genetic kidney diseases and for CKD of unknown origin.

CFH and CFHR Copy Number Variations in C3 Glomerulopathy and Immune Complex-Mediated Membranoproliferative Glomerulonephritis

C3 Glomerulopathy (C3G) and Immune Complex-Mediated Membranoproliferative glomerulonephritis (IC-MPGN) are rare diseases characterized by glomerular deposition of C3 caused by dysregulation of the alternative pathway (AP) of complement. In approximately 20% of affected patients, dysregulation is driven by pathogenic variants in the two components of the AP C3 convertase, complement C3 (C3) and Factor B (CFB), or in complement Factor H (CFH) and Factor I (CFI), two genes that encode complement regulators. Copy number variations (CNVs) involving the CFH-related genes (CFHRs) that give rise to hybrid FHR proteins also have been described in a few C3G patients but not in IC-MPGN patients. In this study, we used multiplex ligation-dependent probe amplification (MLPA) to study the genomic architecture of the CFH-CFHR region and characterize CNVs in a large cohort of patients with C3G (n = 103) and IC-MPGN (n = 96) compared to healthy controls (n = 100). We identified new/rare CNVs resulting in structural variants (SVs) in 5 C3G and 2 IC-MPGN patients. Using long-read single molecule real-time sequencing (SMRT), we detected the breakpoints of three SVs. The identified SVs included: 1) a deletion of the entire CFH in one patient with IC-MPGN; 2) an increased number of CFHR4 copies in one IC-MPGN and three C3G patients; 3) a deletion from CFHR3-intron 3 to CFHR3-3'UTR (CFHR3_{4 - 6} Δ) that results in a FHR3-FHR1 hybrid protein in a C3G patient; and 4) a CFHR3_{1 - 5}-CFHR4₁₀ hybrid gene in a C3G patient. This work highlights the contribution of CFH-CFHR CNVs to the pathogenesis of both C3G and IC-MPGN.

Dengue Virus Infection Presenting as Membranoproliferative Glomerulonephritis Type 1

The renal complications of dengue virus infection cover a wide spectrum of manifestations from acute kidney injury to glomerular injury with nephritic/nephrotic syndrome. Majority of cases remain symptom free and show full recovery. We present a 61-year-old previously healthy male who developed a pyrexial illness with haemolytic anaemia that was diagnosed on the basis of a positive serological test as a case of dengue fever. He received supportive treatment and showed general recovery except for his renal dysfunction that showed persistent proteinuria at 14 gm/24 hours. A kidney biopsy revealed membranoproliferative glomerulonephritis type 1 (MPGN-l). Complete remission was achieved by steroids and mycophenolate mofetil therapy. We provide convincing biopsy evidence that dengue virus is yet another viral cause of MPGN-l and also document its successful management with mycophenolate mofetil and steroids therapy.

Gain-of-function factor H-related 5 protein impairs glomerular complement regulation resulting in kidney damage

Genetic variation within the factor H-related (FHR) genes is associated with the complement-mediated kidney disease, C3 glomerulopathy (C3G). There is no definitive treatment for C3G, and a significant proportion of patients develop end-stage renal disease. The prototypical example is CFHR5 nephropathy, through which an internal duplication within a single CFHR5 gene generates a mutant FHR5 protein (FHR5mut) that leads to accumulation of complement C3 within glomeruli. To elucidate how abnormal FHR proteins cause C3G, we modeled CFHR5 nephropathy in mice. Animals lacking the murine factor H (FH) and FHR proteins, but coexpressing human FH and FHR5mut (hFH-FHR5mut), developed glomerular C3 deposition, whereas mice coexpressing human FH with the normal FHR5 protein (hFH-FHR5) did not. Like in patients, the FHR5mut had a dominant gain-of-function effect, and when administered in hFH-FHR5 mice, it triggered C3 deposition. Importantly, adeno-associated virus vector-delivered homodimeric mini-FH, a molecule with superior surface C3 binding compared to FH, reduced glomerular C3 deposition in the presence of the FHR5mut. Our data demonstrate that FHR5mut causes C3G by disrupting the homeostatic regulation of complement within the kidney and is directly pathogenic in C3G. These results support the use of FH-derived molecules with enhanced C3 binding for treating C3G associated with abnormal FHR proteins. They also suggest that targeting FHR5 represents a way to treat complement-mediated kidney injury.

Leucocytoclastic vasculitis due to acute bacterial endocarditis resolves with antibiotics

Infective endocarditis is associated with a variety of clinical signs, but its association with multisystem vasculitis is rarely reported. A high index of suspicion is necessary to differentiate a primary autoimmune vasculitis from an infectious cause as the wrong treatment can lead to significant morbidity and mortality. We present a 71-year-old female patient with negative blood cultures, on antibiotics for recent bacteraemia, who presented with cutaneous and renal leucocytoclastic vasculitis. Workup revealed a vegetation adjacent to her right atrial pacemaker lead consistent with infective endocarditis and her vasculitis completely resolved with appropriate antibiotics.

C3 glomerulopathy and atypical hemolytic uremic syndrome: an updated review of the literature on alternative complement pathway disorders

The complement system plays a significant role within the pathological process of C3 glomerulopathy (C3GP) and atypical hemolytic uremic syndrome (aHUS). In daily practice, clinicians should differentiate the subgroups of C3GP because of they should apply different treatment modalities. In the past, C3GP was considered as a part of membranoproliferative glomerulonephritis (MPGN). MPGN is defined as glomerular capillary thickening secondary to the synthesis of the new glomerular basement membrane and mesangial cellular hyperplasia with mesangial matrix expansion. Atypical hemolytic uremic syndrome is an ultra-rare disease that can be outlined by the triad of Coombs negative microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Recent advances demonstrated that these diseases share common abnormalities of the control of the alternative complement system. Therefore, nowadays, most researchers advocate that there may be overlap in the pathogenesis of C3GP and aHUS. This review will provide recent novel mechanisms and treatment options in these diseases. For the purposes that we mentioned above and to help clinicians, we aimed to describe the etiology, pathophysiology, and treatment of C3GP and aHUS in this comprehensive review.

Humanized C3 Mouse: A Novel Accelerated Model of C3 Glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is characterized by the alternative-pathway (AP) hyperactivation induced by nephritic factors or complement gene mutations. Mice deficient in complement factor H (CFH) are a classic C3G model, with kidney disease that requires several months to progress to renal failure. Novel C3G models can further contribute to understanding the mechanism behind this disease and developing therapeutic approaches.

METHODS

A novel, rapidly progressing, severe, murine model of C3G was developed by replacing the mouse C3 gene with the human C3 homolog using VelociGene technology. Functional, histologic, molecular, and pharmacologic assays characterize the presentation of renal disease and enable useful pharmacologic interventions in the humanized C3 (C3^hu/hu) mice.

RESULTS

The C3^hu/hu mice exhibit increased morbidity early in life and die by about 5-6 months of age. The C3^hu/hu mice display elevated biomarkers of kidney dysfunction, glomerulosclerosis, C3/C5b-9 deposition, and reduced circulating C3 compared with wild-type mice. Administration of a C5-blocking mAb improved survival rate and offered functional and histopathologic benefits. Blockade of AP activation by anti-C3b or CFB mAbs also extended survival and preserved kidney function.

CONCLUSIONS

The C3^hu/hu mice are a useful model for C3G because they share many pathologic features consistent with the human disease. The C3G phenotype in C3^hu/hu mice may originate from a dysregulated interaction of human C3 protein with multiple mouse complement proteins, leading to unregulated C3 activation via AP. The accelerated disease course in C3^hu/hu mice may further enable preclinical studies to assess and validate new therapeutics for C3G.

Kidney biopsy findings in two patients with TAFRO syndrome: case presentations and review of the literature

Background

TAFRO syndrome is a clinical subtype of idiopathic multicentric Castleman disease (iMCD) that is characterized by thrombocytopenia, anasarca, fever, reticulin myelofibrosis (or renal dysfunction), and organomegaly. TAFRO syndrome has only recently been described, and many clinicians are unaware of this disease, leading to delays in diagnosis and treatment. We present two patients with TAFRO syndrome in whom renal biopsies were performed.

Case presentation

Both patients had subacute onset and exhibited renal insufficiency, edema, anemia, thrombocytopenia, polyserositis and lymphadenopathy over the disease course. However, there were many differences in their clinical manifestations. Case 1 was a 30-year-old woman admitted due to intermittent vaginal bleeding for 3 weeks. Laboratory tests on admission showed severe renal insufficiency (creatinine: 624 μmol/L), severe anemia (Hb: 41 g/L), and moderate thrombocytopenia (61 × 10⁹/L). Case 2 was a 42-year-old man. Acute epigastric pain was his initial complaint, and computed tomography (CT) revealed retroperitoneal exudation around the pancreas. He was diagnosed with acute pancreatitis, and after treatment with a proton pump inhibitor (PPI) and somatostatin, his abdominal pain still recurred. During treatment, renal failure gradually increased, with oliguria, fever, anemia, thrombocytopenia, edema and massive ascites. Lymph node histologies were consistent with the hyaline-vascular (HV) type and mixed type, respectively, and renal histopathologies were consistent with thrombotic microangiopathy (TMA)-like renal lesions and membranoproliferative glomerulonephritis (MPGN), respectively. Their general conditions improved after glucocorticoid therapy, but their renal functions did not recover completely. On the basis of glucocorticoids, second-line treatments with tocilizumab and rituximab, respectively, were applied.

Conclusions

The diagnosis of TAFRO syndrome is based mainly on clinical manifestations and lymph node biopsies. A reliable early diagnosis and appropriate rapid treatment are essential to improve patient outcomes. Clinicians should deepen their understanding of this disease and similar conditions. Once the disease is suspected, lymph node biopsies should be performed as soon as possible. In addition, renal biopsies should be actively performed in patients with renal involvement.

The impact of reclassification of C3 predominant glomerulopathies on diagnostic accuracy, outcome and prognosis in patients with C3 glomerulonephritis

BACKGROUND

C3 glomerulonephritis is a recently described entity with heterogeneous histopathological features. This study was conducted to assess the effect of reclassification of C3 glomerulopathies on renal outcomes, mortality, and response to therapy.

METHODS

We undertook a retrospective analysis of 857 renal biopsies collected at The Canberra Hospital. Samples with predominant C3 staining were reviewed by a renal histopathologist. Of 31 biopsies with predominant C3 staining, 10 fulfilled histological criteria for C3 glomerulonephritis, while the remaining 21 cases were used as C3 Controls.

RESULTS

Aside from a higher incidence of C3 glomerulonephritis in Torres Strait islanders (40% vs 5% C3 Controls, p = 0.04), presentation demographics were similar between the two groups. Median creatinine at diagnosis was higher in patients with C3 glomerulonephritis (253 umol/L IQR 103-333 vs 127 umol/L C3 Controls, IQR 105-182, p = 0.01). Prior to reclassification, a majority of C3 glomerulonephritis cases were diagnosed as membranoproliferative glomerulonephritis (60% vs 5% (C3 Controls) p < 0.01). Electron microscopy demonstrated all C3 glomerulonephritis patients had C3 deposition (100% vs 38% p = 0.02), these deposits were amorphous in nature (50% vs 5% respectively p = 0.007). C3 glomerulonephritis patients had shorter median follow-up (405 days IQR 203-1197 vs 1822 days respectively, IQR 1243-3948, p = 0.02). Mortality was higher in C3 glomerulonephritis patients (30% vs 14% in C3 Controls (log rank p = 0.02)).

CONCLUSION

We have devised a diagnostic and treatment algorithm based on the results of literature review and our current study. Further prospective assessment is required to review diagnostic and treatment outcomes for this disease in Australian centres.

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.

CFHR Gene Variations Provide Insights in the Pathogenesis of the Kidney Diseases Atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy

Sequence and copy number variations in the human CFHR-Factor H gene cluster comprising the complement genes CFHR1, CFHR2, CFHR3, CFHR4, CFHR5, and Factor H are linked to the human kidney diseases atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy. Distinct genetic and chromosomal alterations, deletions, or duplications generate hybrid or mutant CFHR genes, as well as hybrid CFHR-Factor H genes, and alter the FHR and Factor H plasma repertoire. A clear association between the genetic modifications and the pathologic outcome is emerging: CFHR1, CFHR3, and Factor H gene alterations combined with intact CFHR2, CFHR4, and CFHR5 genes are reported in atypical hemolytic uremic syndrome. But alterations in each of the five CFHR genes in the context of an intact Factor H gene are described in C3 glomerulopathy. These genetic modifications influence complement function and the interplay of the five FHR proteins with each other and with Factor H. Understanding how mutant or hybrid FHR proteins, Factor H::FHR hybrid proteins, and altered Factor H, FHR plasma profiles cause pathology is of high interest for diagnosis and therapy.

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.

A case report of recurrent membranoproliferative glomerulonephritis after kidney transplantation due to ventriculoatrial shunt infection

Background

Transplant failure requires the consideration of numerous potential causes including rejection, acute tubular necrosis, infection, and recurrence of the original kidney disease. Kidney biopsy is generally required to approach these differential diagnoses. However, the histopathological findings on their own do not always lead to a definite diagnosis. Consequently, it is crucial to integrate them with clinical findings and patient history when discussing histopathological patterns of injury. The histopathologic finding of a membranoproliferative glomerulonephritis (MPGN) is one of the most challenging constellations since it does not refer to a specific disease entity but rather reflects a pattern of injury that is the result of many different causes. Whilst MPGN is occasionally classified as immune complex mediated, careful evaluation usually reveals an underlying disorder such as chronic infection, plasma cell dyscrasia, complement disorders, and autoimmune disease.

Case presentation

We describe the case of a 43-year-old woman who was referred to us because of a slowly rising serum creatinine 4 years after kidney transplantation. As in the native kidney, the biopsy revealed an MPGN pattern of injury. The cause of this finding had not been established prior to transplantation leading to a classification as idiopathic MPGN in the past. Further workup at the time of presentation and allograft failure revealed chronic infection of a ventriculoatrial shunt as the most probable cause.

Conclusion

This case underlines the fact that MPGN is not a disease but a histopathological description. Consequently, the causative disorder needs to be identified to avoid kidney failure and recurrence after transplantation.

Autoimmune abnormalities of the alternative complement pathway in membranoproliferative glomerulonephritis and C3 glomerulopathy

Membranoproliferative glomerulonephritis (MPGN) is a rare chronic kidney disease associated with complement activation. Recent immunofluorescence-based classification distinguishes between immune complex (IC)-mediated MPGN, with glomerular IgG and C3 deposits, and C3 glomerulopathies (C3G), with predominant C3 deposits. Genetic and autoimmune abnormalities causing hyperactivation of the complement alternative pathway have been found as frequently in patients with immune complex-associated MPGN (IC-MPGN) as in those with C3G. In the last decade, there have been great advances in research into the autoimmune causes of IC-MPGN and C3G. The complement-activating autoantibodies called C3-nephritic factors (C3NeFs), which are present in 40-80% of patients, form a heterogeneous group of autoantibodies that stabilise the C3 convertase or the C5 convertase of the alternative pathway or both. A few patients, mainly with IC-MPGN, carry autoantibodies directed against the two components of the alternative pathway C3 convertase, factors B and C3b. Finally, autoantibodies against factor H, the main regulator of the alternative pathway, have been reported in a small proportion of patients with IC-MPGN or C3G. The identification of distinct pathogenetic patterns leading to kidney injury and of targets in the complement cascade may pave the way for tailored therapies for IC-MPGN and C3G, with specific complement inhibitors in the development pipeline.

Renal Pathologic Findings in TAFRO Syndrome: Is There a Continuum Between Thrombotic Microangiopathy and Membranoproliferative Glomerulonephritis? A Case Report and Literature Review

Background: TAFRO syndrome is a clinical subtype of idiopathic multicentric Castleman disease (iMCD) that is characterized by thrombocytopenia, anasarca, fever and/or elevated serum C-reactive protein, renal dysfunction, and organomegaly.

Case Presentation: A 28-year-old woman with fever, weight gain of 13 kgs, lower extremity edema, hepatosplenomegaly, and multicentric peripheral lymphadenopathy was referred to our center. Laboratory investigations revealed anemia, thrombocytopenia, creatinine at 1.19 mg/dL and hypoalbuminemia at 33 g/L. Proteinuria was measured at 2 g/day including albuminuria at 1.5 g/day. Urinary sediment examination found leukocyturia at 44,000/mL and hematuria at 645,000/mL. Vascular endothelial growth factor (VEGF) level was elevated. A cervical lymph node biopsy found features consistent with the mixed histopathological subtype of iMCD. A renal biopsy revealed a membranoproliferative glomerulonephritis (MPGN) pattern. We initiated 3 days of methylprednisolone pulse-therapy at 1,000 mg per day, followed by prednisone 1 mg/kg/day and evolution was favorable.

Review of Literature: 19 iMCD patients with TAFRO syndrome had undergone a renal biopsy: 8 cases with author's diagnosis consistent with MPGN-like and 11 cases of thrombotic microangiopathy (TMA)-like glomerulopathy without fibrin thrombi in glomerular capillaries or arterioles and without typical biological signs. Clinical, biological, and outcome characteristics were similar between the cases described as having MPGN and TMA-like presentation. After a thorough review of histopathological descriptions for each case, MPGN lesions seems to be the consequences of chronic glomerular endothelial injury in persistent TMA. We suspect that VEGF and IL-6 play a key role in the physiopathology of the spectrum of renal involvement from TMA-like to MPGN observed in TAFRO syndrome.

Conclusion: We present a Caucasian iMCD patient with TAFRO syndrome with renal insufficiency secondary to MPGN, which might be secondary to a chronic TMA-like disease. We suspect that there is a continuum between TMA and MPGN lesions in TAFRO syndrome favored by VEGF and IL-6.

Membranoproliferative glomerulonephritis in Russian population

AIM

Analysis of etiology, clinical and morphological manifestations, approaches to therapy and prognosis of membranoproliferative glomerulonephritis (MPGN).

MATERIALS AND METHODS

Cases of MPGN were retrospectively identified in the period 2000-2017 with subsequent analysis of etiology, clinical data and morphology (including deposits of immunoglobulins (Ig) and C3 complement fractions). The achievement of complete and partial remissions (PR, CR), overall survival, progression (by composite endpoint: decrease in the estimated GFR (eGFR) ≥50% from the baseline or eGFR &lt;15 ml/min/1.73 m2 or the onset of dialysis).

RESULTS

214 cases of MPGN entered the study with the average age of 44±16 years. Most patients had nephrotic syndrome and significant hematuria. In 58.4% of cases, eGFR was &lt;60 mL/min/1.73 m2, and every fifth patient had CKD 4 or 5 stages. The prevalence of MPGN among all biopsy-confirmed glomerulopathies was 9.3%. Idiopathic MPGN (iMPGN) was detected in 30.4% of cases, secondary MSGN (sMPGN) - in 69.6% (autoimmune diseases - 34.1%, infectious diseases - 16.4%, monoclonal gammopathies - 9.3%, complement-mediated damage - 9.8%). Ig+C3+MPGN was mainly associated with autoimmune diseases and infections; C3-glomerulopathy or thrombotic microangiopathy were most often causes of Ig-C3+MPGN; Ig-C3-/Ig+C3-MPGN had heterogeneous etiology. The median follow-up period was 28 [7; 37] months. The 10-year total cumulative patient and renal survival rates were 71 and 50%, respectively (without differences between sMPGN and iMPGN). The frequency of the PR/CR was 50% (iMPGN - 46.2%, sMPGN - 51.3%) depending on the etiology of the MPGN (p=0.049). The cumulative 10-year progression-free renal survival was nearly 100% in cases with PR/CR and 0% in non-responders.

CONCLUSION

MPGN is a severe variant of glomerular damage with a heterogeneous etiological structure and an unfavorable prognosis. Targeted clinical and morphological diagnostics of MPGN allows to identify the cause of the disease in most cases. This approach is reliable for the adequate treatment choice and improvement of outcomes in MPGN.

C5 Convertase Blockade in Membranoproliferative Glomerulonephritis: A Single-Arm Clinical Trial

RATIONALE & OBJECTIVE

Primary membranoproliferative glomerulonephritis (MPGN) is a rare glomerulopathy characterized by complement dysregulation. MPGN progresses rapidly to kidney failure when it is associated with nephrotic syndrome. We assessed the effects of C5 convertase blockade in patients with MPGN and terminal complement activation.

STUDY DESIGN

Prospective off-on-off-on open-label clinical trial.

SETTING & PARTICIPANTS

Consenting patients with immune complex-mediated MPGN (n=6) or C3 glomerulonephritis (n=4) with sC5b-9 (serum complement membrane attack complex) plasma levels>1,000ng/mL and 24-hour proteinuria with protein excretion>3.5g identified from the Italian Registry of MPGN and followed up at the Istituto di Ricerche Farmacologiche Mario Negri IRCCS (Bergamo, Italy) between March 4, 2014, and January 7, 2015.

INTERVENTION

Anti-C5 monoclonal antibody eculizumab administered during 2 sequential 48-week treatment periods separated by one 12-week washout period.

OUTCOMES

Primary outcome was change in 24-hour proteinuria (median of 3 consecutive measurements) at 24 and 48 weeks.

RESULTS

Median proteinuria decreased from protein excretion of 6.03 (interquartile range [IQR], 4.8-12.4) g/d at baseline to 3.74 (IQR, 3.2-4.4) g/d at 24 weeks (P=0.01) and to 5.06 (IQR, 3.1-5.8) g/d (P=0.006) at 48 weeks of treatment, recovered toward baseline during the washout period, and did not significantly decrease thereafter. Hypoalbuminemia, dyslipidemia, and glomerular sieving function improved during the first treatment period. 3 patients achieved partial remission of nephrotic syndrome and all had undetectable C3 nephritic factors before treatment. Mean measured glomerular filtration rate was 69.7±35.2 versus 87.4±55.1 and 75.8±42.7 versus 76.6±44.1mL/min/1.73m² at the start versus the end of the first and second treatment periods, respectively, among all 10 study participants. Unlike C3, sC5b-9 plasma levels normalized during both treatment periods and recovered toward baseline during the washout in all patients.

LIMITATIONS

Single-arm design, small sample size.

CONCLUSIONS

Eculizumab blunted terminal complement activation in all patients with immune complex-mediated MPGN or C3 glomerulonephritis and nephrotic syndrome, but persistently reduced proteinuria in just a subgroup.

TRIAL REGISTRATION

Registered in the EU Clinical Trials Register with study no. 2013-003826-10.

Outcome of membranoproliferative glomerulonephritis and C3-glomerulopathy in children and adolescents

BACKGROUND

Membranoproliferative glomerulonephritis (MPGN) is a rare cause of glomerulopathy in children. Recently, a new classification based on immunohistological features has been established. Infections and anomalies in complement-regulating genes, leading to alternative complement pathway activation, are suspected to trigger the disease. Nevertheless, little is known about optimal treatment and outcome in children with immune-complex-MPGN (IC-MPGN) and C3-glomerulopathy (C3G).

METHODS

The method used is retrospective analysis of clinical, histological, and genetic characteristics of 14 pediatric patients with MPGN in two medical centers.

RESULTS

Mean age of the patients was 10.6 ± 4.5 years. Patients were grouped into C3G (n = 6) and IC-MPGN (n = 8). One patient showed a likely pathogenic variant in the CFHR5 gene. All 10 patients had risk polymorphisms in complement-regulating genes. Most patients were treated with ACE inhibition, steroids, and mycophenolate mofetil. Three patients with C3G received eculizumab. Median follow-up was 2.3 years. After 1 year of disease, three patients (two C3G, one IC-MPGN) reached complete, five patients partial (three IC-MPGN, two C3G), and five patients no remission (four IC-MPGN, one C3G). One patient progressed to end-stage renal disease (ESRD) 6 years after disease onset.

CONCLUSIONS

IC-MPGN and C3G are rare disorders in children. Most patients have signs of complement activation associated with risk polymorphisms or likely pathogenic variants in complement-regulating genes. Steroids and mycophenolate mofetil seem to be effective and for some patients, eculizumab might be a treatment option. Outcome is heterogeneous and precise differentiation between IC-MPGN and C3G is still pending.

Nanoscale Imaging of Kidney Glomeruli Using Expansion Pathology

Kidney glomerular diseases, such as the minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS), and other nephrotic syndromes, are typically diagnosed or confirmed via electron microscopy. Although optical microscopy has been a vital tool to examine clinical specimens for diagnoses in pathology for decades, the optical resolution is constricted by the physical diffraction limit of the optical microscope, which prevents high-resolution investigation of subcellular anatomy, such as of the podocyte tertiary foot processes. Here, we describe a simple, fast, and inexpensive protocol for nanoscale optical imaging of kidney glomeruli. The protocol is based on Expansion Pathology (ExPath), a new principle of microscopy that overcomes optical diffraction limit by chemically embedding specimens into a swellable polymer and physically expanding it homogenously prior to imaging. Our method uses only commercially available reagents, a conventional fluorescence microscope and it can be applied to both fixed-frozen or formalin-fixed paraffin embedded (FFPE) tissue sections. It requires minimal operative experience in a wet lab, optical microscopy and imaging processing. Finally, we also discuss challenges, limitations and prospective applications for ExPath-based imaging of glomeruli.

Unraveling the Molecular Mechanisms Underlying Complement Dysregulation by Nephritic Factors in C3G and IC-MPGN

Membranoproliferative glomerulonephritis (MPGN) was recently classified as C3 glomerulopathies (C3G), and immune-complex (IC) mediated MPGN. Dysregulation of the complement alternative pathway, driven by acquired and/or genetic defects, plays a pathogenetic role in C3G. However, alternative pathway abnormalities were also found in IC-MPGN. The most common acquired drivers are the C3 nephritic factors (C3NeFs), heterogeneous autoantibodies that stabilize the C3 convertase, C3bBb. C3NeFs are traditionally detected by hemolytic assays based on sheep erythrocyte lysis, which however do not provide a direct molecular estimation of C3bBb formation and decay. We set up a microplate/western blot assay that specifically detects and quantifies C3bBb, and its precursor, the C3 proconvertase C3bB, to investigate the complex mechanistic effects of C3NeFs from patients with primary IC-MPGN (n = 13) and C3G (n = 13). In the absence of properdin, 9/26 patients had C3NeF IgGs stabilizing C3bBb against spontaneous and FH-accelerated decay. In the presence of properdin the IgGs of all but one patient had C3bBb-stabilizing activity. Properdin-independent C3NeFs were identified mostly in DDD patients, while properdin-dependent C3NeFs associated with either C3GN or IC-MPGN and with higher incidence of nephrotic syndrome. When we grouped patients based on our recent cluster analysis, patients in cluster 3, with highly electron-dense intramembranous deposits, low C3, and mostly normal sC5b-9 levels, had a higher prevalence of properdin-independent C3NeFs than patients in clusters 1 and 2. Conversely, about 70% of cluster 1 and 2 patients, with subendothelial, subepithelial, and mesangial deposits, low C3 levels and high sC5b-9 levels, had properdin-dependent C3NeFs. The flexibility of the assay allowed us to get deep insights into C3NeF mechanisms of action, showing that: (1) most C3NeFs bind strongly and irreversibly to C3 convertase; (2) C3NeFs and FH recognize different epitopes in C3 convertase; (3) C3NeFs bind rapidly to C3 convertase and antagonize the decay accelerating activity of FH on newly formed complexes; (4) C3NeFs do not affect formation and stability of the C3 proconvertase. Thus, our study provides a molecular approach to detecting and characterizing C3NeFs. The results highlight different mechanisms of complement dysregulation resulting in different complement profiles and patterns of glomerular injury, and this may have therapeutic implications.

[Chronic hepatitis C virus infection: An internist's opinion (Part 1)]

Hepatitis C virus (HCV) infection results in not only chronic hepatitis and subsequent complications as liver cirrhosis and hepatocellular carcinoma, but also in a significant number of other diseases, the so-called extrahepatic manifestations of chronic HCV infection. This is because of viral hepatotropicity and lymphotropicity. The most striking example of the course of chronic HCV infection, in which the infectious and inflammatory processes are concurrent with autoimmune disorders and carcinogenesis, is mixed cryoglobulinemia and B-cell non-Hodgkin's lymphoma. The pathogenesis of these diseases is based on the clonal expansion of B cells, which occurs under their prolonged stimulation with the virus or viral proteins. Part 1 of this review is devoted to the analysis of a correlation of chronic HCV infection with lymphoproliferative and autoimmune disorders, as well as its association with kidney injury.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Respuesta a la farmacoterapia en pacientes con glomerulonefritis membranoproliferativa en una clínica de Barranquilla, Colombia. 2007-2014

Introducción. La glomerulonefritis membranoproliferativa (GnMP) es un patrón de lesión glomerular hipercelular mesangial con adelgazamiento de la membrana basal glomerular y proliferación endocapilar que está mediado por las inmunoglobulinas o el sistema del complemento en el mesangio y endotelio capilar.Objetivo. Evaluar la respuesta a la farmacoterapia en pacientes diagnosticados con GnMP en una clínica de Barranquilla entre los años 2007 y 2014.Materiales y métodos. Estudio de cohorte retrospectivo en el que se evaluaron 58 pacientes con diagnóstico de GnMP por biopsia renal, quienes se clasificaron como respondedores y no respondedores. Se realizó una evaluación de tratamiento estándar según tipo de GnMP: mediado por complemento y mediado por inmunocomplejos e inmunofluorescencia negativa a los 6 y 12 meses de tratamiento.Resultados. La edad promedio de los participantes fue de 35±13 años. De 58 pacientes, 52% eran mujeres, 63% desarrolló enfermedad renal crónica (ERC) al año de evaluación, 25.8% logró remisión (22.4% completa y 3.4% parcial) y 74.2% no logró entrar en remisión.Conclusión. La GnMP es una causa importante de ERC entre la población estudiada. La respuesta al tratamiento inmunosupresor no demostró beneficios estadísticamente significativos, independiente del tipo de GnMP.

An Engineered Complement Factor H Construct for Treatment of C3 Glomerulopathy

Background C3 glomerulopathy (C3G) is associated with dysregulation of the alternative pathway of complement activation, and treatment options for C3G remain limited. Complement factor H (FH) is a potent regulator of the alternative pathway and might offer a solution, but the mass and complexity of FH makes generation of full-length FH far from trivial. We previously generated a mini-FH construct, with FH short consensus repeats 1-5 linked to repeats 18-20 (FH1-5^18-20), that was effective in experimental C3G. However, the serum t1/2 of FH1-5^18-20 was significantly shorter than that of serum-purified FH.Methods We introduced the oligomerization domain of human FH-related protein 1 (denoted by R1-2) at the carboxy or amino terminus of human FH1-5^18-20 to generate two homodimeric mini-FH constructs (FHR1-2^1-5^18-20 and FH1-5^18-20^R1-2, respectively) in Chinese hamster ovary cells and tested these constructs using binding, fluid-phase, and erythrocyte lysis assays, followed by experiments in FH-deficient Cfh-/- mice.Results FHR1-2^1-5^18-20 and FH1-5^18-20^R1-2 homodimerized in solution and displayed avid binding profiles on clustered C3b surfaces, particularly FHR1-2^1-5^18-20 Each construct was >10-fold more effective than FH at inhibiting cell surface complement activity in vitro and restricted glomerular basement membrane C3 deposition in vivo significantly better than FH or FH1-5^18-20 FH1-5^18-20^R1-2 had a C3 breakdown fragment binding profile similar to that of FH, a >5-fold increase in serum t1/2 compared with that of FH1-5^18-20, and significantly better retention in the kidney than FH or FH1-5^18-20Conclusions FH1-5^18-20^R1-2 may have utility as a treatment option for C3G or other complement-mediated diseases.