Mycophenolate Mofetil in Combination with Steroids for Treatment of C3 Glomerulopathy: A Case Series

Complement gene mutations in children with C3 glomerulopathy: do they affect the response to mycophenolate mofetil?

BACKGROUND

C3 glomerulopathy (C3G) is a complement-mediated disease. Although genetic studies are not required for diagnosis, they are valuable for treatment planning and prognosis prediction. The aim of this study is to investigate the clinical phenotypes, kidney survival, and response to mycophenolate mofetil (MMF) treatment in pediatric C3G patients with and without mutations in complement-related genes.

METHODS

Sixty pediatric C3G patients were included, divided into two groups based on complement-related gene mutations. Demographic and clinical-pathological findings, treatment modalities, and outcome data were compared, and Kaplan-Meier analysis was performed for kidney survival.

RESULTS

Out of the 60 patients, 17 had mutations. The most common mutation was in the CFH gene (47%). The mean age at diagnosis was higher in the group with mutation (12.9 ± 3.6 vs. 11.2 ± 4.1 years, p = 0.039). While the patients without mutation most frequently presented with nephritic syndrome (44.2%), the mutation group was most likely to have asymptomatic urinary abnormalities (47.1%, p = 0.043). Serum parameters and histopathological characteristics were similar, but hypoalbuminemia was more common in patients without mutation. During 45-month follow-up,10 patients progressed to chronic kidney disease stage 5 (CKD5), with 4 having genetic mutation. The time to develop CKD5 was longer in the mutation group but not significant. MMF treatment had no effect on progression in either group.

CONCLUSIONS

This study is the largest pediatric C3G study examining the relationship between genotype and phenotype. We showed that the mutation group often presented with asymptomatic urinary abnormalities, was diagnosed relatively late but was not different from the without mutation group in terms of MMF treatment response and kidney survival.

Clinical characteristics and outcomes of immune-complex membranoproliferative glomerulonephritis and C3 glomerulopathy in Japanese children

BACKGROUND

Membranoproliferative glomerulonephritis (MPGN) can be divided into immune-complex MPGN (IC-MPGN) and C3 glomerulopathy (C3G), which includes dense deposit disease (DDD) and C3 glomerulonephritis (C3GN). These conditions result from abnormalities in different complement pathways and may lead to different prognoses. However, there are limited studies describing the respective clinical courses.

METHODS

In this study, Japanese pediatric patients diagnosed with MPGN based on kidney biopsies conducted between February 2002 and December 2022 were reclassified as having IC-MPGN or C3G (DDD or C3GN). We retrospectively analyzed the clinical characteristics and outcomes of these patients.

RESULTS

Out of 25 patients with MPGN, three (12.0%) were diagnosed with DDD, 20 (80.0%) with C3GN, and two (8.0%) with IC-MPGN. There were 13 (65.0%) patients and one (33.3%) patient in remission after treatment for C3GN and DDD, respectively, and no patients with IC-MPGN achieved remission. The median follow-up period was 5.3 (2.5-8.9) years, and none of the patients in either group progressed to an estimated glomerular filtration rate < 15 ml/min/1.73 m2. Patients with C3GN presenting mild to moderate proteinuria (n = 8) received a renin-angiotensin system inhibitor (RAS-I) alone, and these patients exhibited a significant decrease in the urinary protein creatinine ratio and a notable increase in serum C3 levels at the last follow-up.

CONCLUSIONS

Most patients with MPGN were diagnosed with C3GN. The remission rate for C3GN was high, and no patients developed kidney failure during the approximately 5-year follow-up. Additionally, patients with C3GN with mild to moderate proteinuria had good outcomes with RAS-I alone, but continued vigilance is necessary to determine long-term prognosis.

Recurrent C3 glomerulopathy after kidney transplantation

The complement system is part of innate immunity and is pivotal in protecting the body against pathogens and maintaining host homeostasis. Activation of the complement system is triggered through multiple pathways, including antibody deposition, a mannan-binding lectin, or activated complement deposition. C3 glomerulopathy (C3G) is a rare glomerular disease driven by complement dysregulation with high post-transplantation recurrence rates. Its treatment is mainly based on immunosuppressive therapies, specifically mycophenolate mofetil and glucocorticoids. Recent years have seen significant progress in understanding complement biology and its role in C3G pathophysiology. New complement-tergeting treatments have been developed and initial trials have shown promising results. However, challenges persist in C3G, with recurrent post-transplantation cases leading to suboptimal outcomes. This review discusses the pathophysiology and management of C3G, with a focus on its recurrence after kidney transplantation.

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.

Targeting the Complement Pathway in Kidney Transplantation

The complement system is paramount in the clearance of pathogens and cell debris, yet is increasingly recognized as a key component in several pathways leading to allograft injury. There is thus a growing interest in new biomarkers to assess complement activation and guide tailored therapies after kidney transplantation (KTx). C5 blockade has revolutionized post-transplant management of atypical hemolytic uremic syndrome, a paradigm of complement-driven disease. Similarly, new drugs targeting the complement amplification loop hold much promise in the treatment and prevention of recurrence of C3 glomerulopathy. Although unduly activation of the complement pathway has been described after brain death and ischemia reperfusion, any clinical attempts to mitigate the ensuing renal insults have so far provided mixed results. However, the intervention timing, strategy, and type of complement blocker need to be optimized in these settings. Furthermore, the fast-moving field of ex vivo organ perfusion technology opens new avenues to deliver complement-targeted drugs to kidney allografts with limited iatrogenic risks. Complement plays also a key role in the pathogenesis of donor-specific ABO- and HLA-targeted alloantibodies. However, C5 blockade failed overall to improve outcomes in highly sensitized patients and prevent the progression to chronic antibody-mediated rejection (ABMR). Similarly, well-conducted studies with C1 inhibitors in sensitized recipients yielded disappointing results so far, in part, because of subtherapeutic dosage used in clinical studies. The emergence of new complement blockers raises hope to significantly reduce the negative effect of ischemia reperfusion, ABMR, and nephropathy recurrence on outcomes after KTx.

Clinical Safety and Efficacy of Pegcetacoplan in a Phase 2 Study of Patients with C3 Glomerulopathy and Other Complement-Mediated Glomerular Diseases

Introduction

Dysregulated complement activation is likely the primary driver of disease in C3 glomerulopathy (C3G) and contributes to other complement-mediated diseases, including immunoglobulin A nephropathy (IgAN), lupus nephritis (LN), and primary membranous nephropathy (PMN). No complement inhibitors are proven to halt disease progression in these diseases. Pegcetacoplan, a targeted C3 and C3b inhibitor, may mitigate complement-mediated kidney damage in C3G and other glomerular diseases in which complement may have a pathogenic role.

Methods

This open-label, phase 2, 48-week study evaluated the preliminary efficacy and safety of subcutaneous pegcetacoplan for patients with complement-mediated glomerular diseases. The primary end point was proteinuria reduction, measured as 24-hour urine protein-to-creatinine ratio. Secondary end points included remission status, changes in estimated glomerular filtration rate (eGFR), and pharmacodynamic biomarkers. Treatment-emergent adverse events (TEAEs) were monitored.

Results

Efficacy results for the C3G cohort are reported herein, along with safety results for the study population. In the C3G cohort, mean proteinuria reduction from baseline to week 48 was 50.9% in the intent-to-treat (ITT) population (n = 7) and 65.4% in the per-protocol (PP) population (n = 4). Mean serum albumin normalized and mean eGFR was stable over 48 weeks. Mean serum C3 levels increased 6-fold and mean soluble C5b-9 levels decreased by 57.3% at week 48. The most common adverse events (AEs) were upper respiratory tract infection, injection site erythema, nausea, and headache. No meningitis or sepsis cases were reported, and no serious treatment-related AEs were observed.

Conclusion

Pegcetacoplan may provide therapeutic benefit for C3G and has a favorable safety profile across the 4 glomerular diseases studied.

Genetic investigation of Nordic patients with complement-mediated kidney diseases

Background

Complement activation in atypical hemolytic uremic syndrome (aHUS), C3 glomerulonephropathy (C3G) and immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) may be associated with rare genetic variants. Here we describe gene variants in the Swedish and Norwegian populations.

Methods

Patients with these diagnoses (N=141) were referred for genetic screening. Sanger or next-generation sequencing were performed to identify genetic variants in 16 genes associated with these conditions. Nonsynonymous genetic variants are described when they have a minor allele frequency of <1% or were previously reported as being disease-associated.

Results

In patients with aHUS (n=94, one also had IC-MPGN) 68 different genetic variants or deletions were identified in 60 patients, of which 18 were novel. Thirty-two patients had more than one genetic variant. In patients with C3G (n=40) 29 genetic variants, deletions or duplications were identified in 15 patients, of which 9 were novel. Eight patients had more than one variant. In patients with IC-MPGN (n=7) five genetic variants were identified in five patients. Factor H variants were the most frequent in aHUS and C3 variants in C3G. Seventeen variants occurred in more than one condition.

Conclusion

Genetic screening of patients with aHUS, C3G and IC-MPGN is of paramount importance for diagnostics and treatment. In this study, we describe genetic assessment of Nordic patients in which 26 novel variants were found.

[Diagnosis and treatment of glomerular diseases with a membranoproliferative glomerulonephritis (MPGN) pattern of injury]

Membranoproliferative glomerulonephritis (MPGN) represents a heterogeneous group of diseases. The common feature of a membranoproliferative lesion pattern in the kidney biopsy can either be idiopathic/primary or-much more frequently-have a secondary cause. The historical classification into MPGN types I to III has largely been abandoned and replaced in recent years by a pathogenesis-oriented classification. A MPGN with C1q, C3 and/or C4 deposits on light microscopy is referred to as immune complex GN (IC-GN), while a MPGN with dominant C3 deposits is referred to as C3 glomerulopathy (C3G). C3G is further divided into C3 glomerulonephritis (C3GN) and dense deposit disease (DDD). These diagnoses can only be made by a kidney biopsy. Possible causes of MPGN are chronic infections (especially hepatitis B and C, bacterial infections, infections with protozoa), autoimmune diseases (especially lupus, rheumatoid arthritis) or malignancies (especially hematological malignancies). Particularly in the case of C3G a comprehensive analysis of the complement system components is strongly recommended. Due to the low incidence and the heterogeneous clinical appearance of MPGN therapeutic decisions must be made individually; an optimal general therapy is unknown, except that supportive treatment as with other glomerular diseases should be optimized. In the case of a secondary MPGN it is generally recommended to treat the potential cause of the MPGN. If significant proteinuria persists and eGFR remains > 30 ml/min/1.73 m2, treatment with systemic steroids and mycophenolate mofetil is recommended. Other treatment options on an individual level after evaluation and discussion of the risk-benefit ratio with the patient are rituximab and eculizumab. Rapidly progressive MPGN should be treated like ANCA-associated vasculitis. The recurrence rates after kidney transplantation are very high and treatment is challenging.

Glomerular Diseases Across Lifespan: Key Differences in Diagnostic and Therapeutic Approaches

Glomerular diseases are common causes of chronic kidney disease in childhood, adolescence, and adulthood. The epidemiology of glomerular diseases differs between different age groups, with minimal change disease being the leading cause of nephrotic syndrome in childhood, while membranous nephropathy and focal segmental glomerulosclerosis are more common in adulthood. IgA vasculitis is also more common in childhood. Moreover, there is a difference in disease severity with more children presenting with a relapsing form of nephrotic syndrome and a more acute presentation of antineutrophil cytoplasmic antibody-associated vasculitis and concomitant glomerulonephritis, as highlighted by the higher percentage of cellular crescents on kidney biopsy specimens in comparison with older patients. There is also a female preponderance in antineutrophil cytoplasmic antibody-associated vasculitis and more children present with tracheobroncholaryngeal disease. This article aims to summarize differences in the presentation of different glomerular diseases that are encountered commonly by pediatric and adult nephrologists and potential differences in the management.

Clinical Profiles and Patterns of Kidney Disease Progression in C3 Glomerulopathy

Key Points

Kidney survival in C3 glomerulopathy is significantly higher in patients with a disease chronicity score <4 and proteinuria <3.5 g/d, regardless of baseline eGFR. A faster eGFR decline in C3 glomerulopathy is associated with higher probability of kidney failure. Patients with glomerulopathy with a progressive reduction in proteinuria over time did not reach kidney failure.

Background

C3 glomerulopathy is a rare kidney disease, which makes it difficult to collect large cohorts of patients to better understand its variability. The aims of this study were to describe the clinical profiles and patterns of progression of kidney disease.

Methods

This was a retrospective, observational cohort study. Patients diagnosed with C3 glomerulopathy between 1995 and 2020 were enrolled. Study population was divided into clinical profiles by combining the following predictors: eGFR under/above 30 ml/min per 1.73 m2, proteinuria under/above 3.5 g/d, and histologic chronicity score under/above 4. The change in eGFR and proteinuria over time was evaluated in a subgroup with consecutive measurements of eGFR and proteinuria.

Results

One hundred and fifteen patients with a median age of 30 years (interquartile range 19–50) were included. Patients were divided into eight clinical profiles. Kidney survival was significantly higher in patients with a chronicity score <4 and proteinuria <3.5 g/d, both in those presenting with an eGFR under/above 30 ml/min per 1.73 m2. The median eGFR slope of patients who reached kidney failure was −6.5 ml/min per 1.73 m2 per year (interquartile range −1.6 to −17). Patients who showed a reduction in proteinuria over time did not reach kidney failure. On the basis of the rate of eGFR decline, patients were classified as faster eGFR decline (≥5 ml/min per 1.73 m2 per year), slower (<5 ml/min per 1.73 m2 per year), and those without decline. A faster eGFR decline was associated with higher probability of kidney failure.

Conclusions

Kidney survival is significantly higher in patients with a chronicity score <4 and proteinuria <3.5 g/d regardless of baseline eGFR, and a faster rate of decline in eGFR is associated with higher probability of kidney failure.

Propensity score-matched analysis of long-term outcomes for living kidney donation in alternative complement pathway diseases: a pilot study

BACKGROUND

Atypical hemolytic syndrome (aHUS) and C3 glomerulopathy (C3G) are complement-mediated rare diseases with excessive activation of the alternative pathway. Data to guide the evaluation of living-donor candidates for aHUS and C3G are very limited. The outcomes of living donors to recipients with aHUS and C3G (Complement disease-living donor group) were compared with a control group to improve our understanding of the clinical course and outcomes of living donation in this context.

METHODS

Complement disease-living donor group [n = 28; aHUS(53.6%), C3G(46.4%)] and propensity score-matched control-living donor group (n = 28) were retrospectively identified from 4 centers (2003-2021) and followed for major cardiac events (MACE), de novo hypertension, thrombotic microangiopathy (TMA), cancer, death, estimated glomerular filtration rate (eGFR) and proteinuria after donation.

RESULTS

None of the donors for recipients with complement-related kidney diseases experienced MACE or TMA whereas two donors in the control group developed MACE (7.1%) after 8 (IQR, 2.6-12.8) years (p = 0.15). New-onset hypertension was similar between complement disease and control donor groups (21.4% vs 25%, respectively, p = 0.75). There were no differences between study groups regarding last eGFR and proteinuria levels (p = 0.11 and p = 0.70, respectively). One related donor for a recipient with complement-related kidney disease developed gastric cancer and another related donor developed a brain tumor and died in the 4th year after donation (2, 7.1% vs none, p = 0.15). No recipient had donor-specific human leukocyte antigen antibodies at the time of transplantation. Median follow-up period of transplant recipients was 5 years (IQR, 3-7). Eleven (39.3%) recipients [aHUS (n = 3) and C3G (n = 8)] lost their allografts during the follow-up period. Causes of allograft loss were chronic antibody-mediated rejection in 6 recipients and recurrence of C3G in 5. Last serum creatinine and last eGFR of the remaining patients on follow up were 1.03 ± 038 mg/dL and 73.2 ± 19.9 m/min/1.73 m2 for aHUS patients and 1.30 ± 0.23 mg/dL and 56.4 ± 5.5 m/min/1.73 m2 for C3G patients.

CONCLUSION

The present study highlights the importance and complexity of living related-donor kidney transplant for patients with complement-related kidney disorders and motivates the need for further research to determine the optimal risk-assessment for living donor candidates to recipients with aHUS and C3G.

Recurrence of immune complex and complement-mediated membranoproliferative glomerulonephritis in kidney transplantation

INTRODUCTION

Membranoproliferative glomerulonephritis (MPGN) represents a histologic pattern of glomerular injury that may be due to several aetiologies. Few studies have comprehensively analysed the recurrence of MPGN according to the current classification system.

METHODS

We collected a multicentre, retrospective cohort of 220 kidney graft recipients with biopsy-proven native kidney disease due to MPGN between 1981 and 2021 in 11 hospitals. Demographic, clinical and histologic parameters of prognostic interest were collected. The main outcomes were time to kidney failure, time to recurrence of MPGN and disease remission after recurrence.

RESULTS

The study group included 34 complement-mediated and 186 immune complex-mediated MPGN. A total of 81 patients (37%) reached kidney failure in a median follow-up of 79 months. The main predictors of this event were the development of rejection episodes and disease recurrence. In all, 54 patients (25%) had a disease recurrence in a median of 16 months after kidney transplantation. The incidence of recurrence was higher in patients with dysproteinaemia (67%) and complement-mediated MPGN (62%). In the multivariable model, complement-mediated MPGN emerged as a predictor of recurrence. A total of 33 patients reached kidney failure after recurrence. The main determinants of no remission were early time to recurrence (<15 months), estimated glomerular filtration rate <30 mL/min/1.73 m2 and serum albumin <3.5 g/dL at the time of recurrence.

CONCLUSIONS

One-fourth of the patients with native kidney disease due to MPGN developed clinical recurrence in the allograft, especially in cases with complement-mediated disease or in those associated with dysproteinaemia. The kidney outcomes of disease recurrence with currently available therapies are heterogeneous and thus more effective and individualized therapies are needed.

Change of circulating lymphocyte subsets is related to disease activity and secondary infection in children with primary nephrotic syndrome-a retrospective study

BACKGROUND

Primary nephrotic syndrome (PNS) is an immune-mediated glomerular disease that often reoccurs. However, the characteristics of circulating lymphocyte subsets in PNS children remain unclear. Immunosuppressive therapy can lead to temporary or persistent remissions, but also increases the risk of infection, and whether the circulating lymphocyte subsets can be used to predict the secondary infection also remains unclear. Here, we explored the distribution of lymphocyte subpopulations in the different stages of PNS, and its predictive value of secondary infection in pediatric patients.

METHODS

We included 89 children who were first PNS episodes or diagnosed with PNS admitted to Nanfang Hospital from September 2019 to April 2021, and 19 healthy children were recruited as controls (C). PNS patients were divided into three groups according to their serum biochemical tests: active group (A), partial remission (PR) group, and complete remission (CR) group. PNS patients with infection symptoms were divided into a co-infection group, others were divided into the non-infection group. The peripheral lymphocyte subsets were analyzed by flow cytometry. The relationship between the peripheral lymphocyte subsets and PNS activity or infection was analyzed.

RESULTS

Compared to the healthy controls, the PNS patients' CD8⁺CD28⁺ T cell (T_C) (C: 16.6%, 450.8/µL; 
A: 29.1%, P=0.000, 886.1/µL, P=0.012; PR: 25.7%, P=0.000, 817.3/µL, P=0.012; CR: 24.9%, P=0.001, 747.9/µL, P=0.020), and CD4⁺CD45RO⁺ ("memory" helper) T cells (C: 13.2%, 358.9/µL; A: 15.7%, P=0.036, 578.7/µL, P=0.001; PR: 17.6%, P=0.002, 610.0/µL, P=0.000; CR: 13.7%, P=0.676, 398.1/µL, P=0.525) were elevated. In addition, the regulatory T cells counts (non-infection: 117.9/µL; Co-infection: 73.3/µL, P=0.001) were significantly lower in patients with infection. We found that the predictive value measured by the area under the curve (AUC) showed that the AUC (t) T_reg cell counts (61.5-84.5%) were almost always higher than the AUC for the (t) CD4⁺ T cell counts (55.1-77.1%).

CONCLUSIONS

In this study, we found that T cell subpopulations had different characteristics in PNS during different disease phases. The CD8⁺CD28⁺ T cells, and CD4⁺CD45RO⁺ T cells increased at the disease quiescence of PNS. Moreover, CD4⁺ T cell subsets (regulatory T cell <82.5/µL) had higher predictive value than CD4⁺ T cell counts for PNS infection.

C3 glomerulopathy: Understanding an ultra-rare complement-mediated renal disease

C3 glomerulopathy (C3G) describes a pathologic pattern of injury diagnosed by renal biopsy. It is characterized by the dominant deposition of the third component of complement (C3) in the renal glomerulus as resolved by immunofluorescence microscopy. The underlying pathophysiology is driven by dysregulation of the alternative pathway of complement in the fluid-phase and in the glomerular microenvironment. Characterization of clinical features and a targeted evaluation for indices and drivers of complement dysregulation are necessary for optimal patient care. Autoantibodies to the C3 and C5 convertases of complement are the most commonly detected drivers of complement dysregulation, although genetic mutations in complement genes can also be found. Approximately half of patients progress to end-stage renal disease within 10 years of diagnosis, and, while transplantation is a viable option, there is high risk for disease recurrence and allograft failure. This poor outcome reflects the lack of disease-specific therapy for C3G, relegating patients to symptomatic treatment to minimize proteinuria and suppress renal inflammation. Fortunately, the future is bright as several anti-complement drugs are currently in clinical trials.

Remissions and progression of C3 glomerulopathy

Aim. To analyze the outcomes of C3-glomerulopathy (C3-GP) and determine the associated factors. Materials and methods. A retrospective single-center study included 60 patients with newly diagnosed C3-GP (with primary C3-GP pC3-GP 82%). Of these, 48 (80%) patients had clinical data to assess the following disease outcomes: development of remission and disease progression (by a composite endpoint that included initiation of chronic dialysis or a decrease in estimated glomerular filtration rate eGFR 15 mL/min/1.73 m2 or a decrease in eGFR30% of baseline at the time of renal biopsy). The median follow-up period was 25 (7; 52) months. Results. At early follow-up (median 4 [3; 9] months) remission was registered in 35% of patients; at the end of follow-up, in 48% (for pC3-GP, 32 and 41%). Disease progression occurred in 17 patients. In the overall group the likelihood of achieving early remission was higher with treatment (Exp=6.4, 95% confidence interval CI 1.429.3; p=0.017). Early remission was associated with the presence of remission at the end of follow-up (Exp=6.3, 95% CI 2.218.4; p=0.001). Specific treatment (Exp=0.308, 95% CI 0.1080.881; p=0.028) and late remission (Exp=0.079, 95% CI 0.0170.368; p=0.001) were associated with reduced risk of disease progression in multivariable models (adjusted for eGFR, mean blood pressure). The same results were obtained for the group of patients with pC3-GP. Conclusion. C3-GP is a variant of severe complement-mediated glomerular damage with unfavorable renal prognosis, which requires timely personalized expert-level diagnostics with clarification of etiopathogenesis of the disease followed by therapy aimed at achieving remission to improve outcomes.

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.

An Interdisciplinary Diagnostic Approach to Guide Therapy in C3 Glomerulopathy

Since the re-classification of membranoproliferative glomerulonephritis the new disease entity C3 glomerulopathy is diagnosed if C3 deposition is clearly dominant over immunoglobulins in immunohistochemistry or immunofluorescence. Although this new definition is more orientated at the pathophysiology as mediated by activity of the alternative complement pathway C3 glomerulopathy remains a heterogenous group of disorders. Genetic or autoimmune causes are associated in several but not in all patients with this disease. However, prognosis is poorly predictable, and clinicians cannot directly identify patients that might benefit from therapy. Moreover, therapy may range from supportive care alone, unspecific immune suppression, plasma treatment, or plasma exchange to complement inhibition. The current biopsy based diagnostic approaches sometimes combined with complement profiling are not sufficient to guide clinicians neither (i) whether to treat an individual patient, nor (ii) to choose the best therapy. With this perspective, we propose an interdisciplinary diagnostic approach, including detailed analysis of the kidney biopsy for morphological alterations and immunohistochemical staining, for genetic analyses of complement genes, complement activation patterning in plasma, and furthermore for applying novel approaches for convertase typing and complement profiling directly in renal tissue. Such a combined diagnostic approach was used here for a 42-year-old female patient with a novel mutation in the Factor H gene, C3 glomerulopathy and signs of chronic endothelial damage. We present here an approach that might in future help to guide therapy of renal diseases with relevant complement activation, especially since diverse new anti-complement agents are under clinical investigation.

Hypocomplementemic Atypical IgA Vasculitis: A Case Report

IgA vasculitis (IgAV, also known as Henoch-Schönlein purpura or HSP) is a vasculitis of small vessels involving multiple organs, particularly of the joints, gastrointestinal tract, skin, and kidneys. Growing laboratory evidence has shown that complement plays a key role in the pathogenesis of IgAV, although direct evidence of this association in patients is lacking. We report a child with IgAV associated with clinical features of hypertension, nephrotic range proteinuria, acute kidney injury, and low serum C3, with histopathologic findings on renal biopsy of membranoproliferative glomerulonephritis with C3 and IgA co-dominance, and extensive complement derangements. This case report suggests that complement modifies the pathogenesis of IgAV, and further investigation into complement-targeted therapy in cases of refractory IgAV may be beneficial.

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.

C3 glomerulopathy associated with monoclonal gammopathy: impact of chronic histologic lesions and beneficial effects of clone-targeted therapies

INTRODUCTION

C3 glomerulopathy associated with monoclonal gammopathy (C3G-MIg) is a rare entity. Herein, we analyzed the clinical and histologic features of a cohort of C3G-MIg patients.

METHODS

Retrospective, multicenter, observational study. Patients diagnosed with C3G-MIg between 1995-2021 were enrolled. All had genetic studies of the alternative complement pathway. The degree of disease activity and chronicity was analyzed using the C3G histologic index. Descriptive statistics and propensity-score matching (PSM) analysis were used to evaluate the main outcome of the study (kidney failure [KF]).

RESULTS

The study group included 23 patients: median age 63 years (IQR 48-70), 57% males. IgG kappa was the most frequent MIg (65%). The diagnosis of C3G-MIg was made in transplanted kidneys in 7 patients (30%). Five (22%) had C3 nephritic factor and 5 (22%) anti-factor H antibodies. One patient carried a pathogenic variant in CFH gene.During a follow-up of 40 months (IQR 14-69), 9 patients (39%) reached KF, and these patients had a significant higher total chronicity score in kidney biopsy. Patients who received clone-targeted therapy had a significant higher survival compared to other management. Those who achieved hematological response had a significant higher kidney survival. Outcome was remarkably poor in kidney transplant recipients, 5 of them (71%) reaching KF.By PSM (adjusting for age, kidney function, proteinuria and chronicity score), no significant differences were observed in kidney survival between C3G patients with/without MIg.

CONCLUSIONS

The C3G histologic index can be used in patients with C3G-MIg to predict kidney prognosis, with higher chronicity scores being associated with worse outcomes. Clone-targeted therapies and the development of hematological response, are associated with better kidney prognosis.

Predictors of poor kidney outcome in children with C3 glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is characterized by heterogeneous clinical presentation, outcome, and predominant C3 accumulation in glomeruli without significant IgG. There is scarce outcome data regarding childhood C3G. We describe clinical and pathological features, treatment and outcomes, and risk factors for progression to chronic kidney disease stage 5 (CKD5) in the largest pediatric series with biopsy-proven C3G.

METHODS

Sixty pediatric patients with C3G from 21 referral centers in Turkey were included in this retrospective study. Patients were categorized according to CKD stage at last visit as CKD5 or non-CKD5. Demographic data, clinicopathologic findings, treatment, and outcome data were compared and possible risk factors for CKD5 progression determined using Cox proportional hazards model.

RESULTS

Mean age at diagnosis was 10.6 ± 3.0 years and follow-up time 48.3 ± 36.3 months. Almost half the patients had gross hematuria and hypertension at diagnosis. Nephritic-nephrotic syndrome was the commonest presenting feature (41.6%) and 1/5 of patients presented with nephrotic syndrome. Membranoproliferative glomerulonephritis was the leading injury pattern, while 40 patients had only C3 staining. Patients with DDD had significantly lower baseline serum albumin compared with C3GN. Eighteen patients received eculizumab. Clinical remission was achieved in 68.3%. At last follow-up, 10 patients (16.6%) developed CKD5: they had lower baseline eGFR and albumin and higher frequency of nephrotic syndrome and dialysis requirement than non-CKD5 patients. Lower serum albumin and eGFR at diagnosis were independent predictors for CKD5 development.

CONCLUSIONS

Children with C3G who have impaired kidney function and hypoalbuminemia at diagnosis should be carefully monitored for risk of progression to CKD5. Graphical abstract.

Longitudinal change in proteinuria and kidney outcomes in C3 glomerulopathy

INTRODUCTION

The association between a change in proteinuria over time and its impact in kidney prognosis has not been analyzed in C3 glomerulopathy. This study aims to investigate the association between the longitudinal change in proteinuria and the risk of kidney failure.

METHODS

Retrospective, multicenter observational cohort study in 35 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases (GLOSEN). Patients diagnosed with C3 glomerulopathy between 1995 and 2020 were enrolled. A joint modeling of linear mixed-effects models was applied to assess the underlying trajectory of a repeatedly measured proteinuria, and a Cox model to evaluate the association of this trajectory with the risk of kidney failure.

RESULTS

The study group consisted of 85 patients, 70 C3 glomerulonephritis and 15 dense deposit disease, with a median age of 26 years (range 13-41). During a median follow-up of 42 months, 25 patients reached kidney failure. The longitudinal change in proteinuria showed a strong association with the risk of this outcome, with a doubling of proteinuria levels resulting in a 2.5-fold increase of the risk. A second model showed that a ≥ 50% proteinuria reduction over time was significantly associated with a lower risk of kidney failure (HR: 0.79; 95% CI : 0.56-0.97; p < 0.001). This association was also found when the ≥50% proteinuria reduction was observed within the first 6 and 12 months of follow-up.

CONCLUSION

The longitudinal change in proteinuria is strongly associated with the risk of kidney failure. The change in proteinuria over time can provide clinicians a dynamic prediction of kidney outcomes.

Therapy and outcomes of C3 glomerulopathy and immune-complex membranoproliferative glomerulonephritis

BACKGROUND

Data on therapy and outcome of dense deposit disease (DDD), C3 glomerulonephritis (C3GN), and immune-complex MPGN (IC-MPGN) in children are limited.

METHODS

In this retrospective single-center study from 2007 to 2019, kidney biopsies were reviewed to include patients aged <18-years with C3 glomerulopathy and IC-MPGN. Initial immunosuppression comprised prednisolone, mycophenolate mofetil (n = 51), tacrolimus (n = 11), and/or IV cyclophosphamide (n = 20). Clinicopathological features, response to therapy, and adverse outcome (eGFR_cr < 15 mL/min/1.73 m² or death) were evaluated.

RESULTS

A total of 92 patients were classified as DDD (n = 48, 52.2%), C3GN (n = 26, 28.3%), and IC-MPGN (n = 18, 19.6%) by immunohistochemistry and electron microscopy; 8 patients with DDD were misclassified as IC-MPGN on immunofluorescence. At last follow-up (median 4.3 years), complete or partial remission occurred in 28.5, 36.1, and 16.7% patients with DDD, C3GN, and IC-MPGN, respectively. Serum albumin at onset < 2.5 g/dL (HR = 0.29, P = 0.005) and persistently low serum C3 (HR = 0.34, P = 0.02) were associated with lack of remission. The 5-year kidney survival was 62.6, 85.5, and 88.5% in patients with DDD, C3GN, and IC-MPGN, respectively (log-rank, P = 0.006). Presentation as rapidly progressive GN (HR = 11.2, P < 0.001), age > 10 years at onset (HR = 4.0, P = 0.004), and DDD (HR = 4.2, P = 0.02) were independently associated with adverse outcome; achieving remission was protective (HR = 0.04; P < 0.001).

CONCLUSION

Outcome in patients with C3 glomerulopathy and IC-MPGN was unsatisfactory, and only a small proportion of patients achieved complete or partial remission. Patients with DDD were more likely to present with rapidly progressive GN and were at higher risk of adverse outcomes, including kidney failure.

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.

Validation of a Histologic Scoring Index for C3 Glomerulopathy

RATIONALE & OBJECTIVE

A previous study that evaluated associations of kidney biopsy findings with disease progression in patients with C3 glomerulopathy (C3G) proposed a prognostic histologic index (C3G-HI) that has not yet been validated. Our objective was to validate the performance of the C3G-HI in a new patient population.

STUDY DESIGN

Multicenter, retrospective cohort study.

SETTING & PARTICIPANTS

111 patients fulfilling diagnostic criteria of C3G between January 1995 and December 2019, from 33 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases (GLOSEN).

PREDICTORS

Demographic, clinical parameters, C3G-HI total activity score, and the C3G-HI total chronicity score.

OUTCOME

Time to kidney failure.

ANALYTICAL APPROACH

Intraclass correlation coefficients and κ statistic were used to summarize inter-rater reproducibility for assessment of histopathology in kidney biopsies. The nonlinear relationships of risk of kidney failure with the total activity score and total chronicity score were modeled using Cox proportional hazards analysis that incorporated cubic splines.

RESULTS

The study group included 93 patients with C3 glomerulonephritis and 18 with dense-deposit disease. Participants had an overall meanage of 35±22 (SD) years. Forty-eight patients (43%) developed kidney failure after a mean follow-up of 65±27 months. The overall inter-rater reproducibility was very good for the total activity score (intraclass correlation coefficient [ICC]=0.63) and excellent for total chronicity score (ICC=0.89). Baseline estimated glomerular filtration rate (eGFR), 24-hour proteinuria, and treatment with immunosuppression were the main determinants of kidney failure in a model with only clinical variables. Only tubular atrophy and interstitial fibrosis were identified as predictors in a model with histological variables. When the total activity score and total chronicity score were added to the model, only the latter was identified as an independent predictor of kidney failure.

LIMITATIONS

Only a subset of the kidney biopsies was centrally reviewed. Residual confounding.

CONCLUSIONS

We validated the performance of C3G-HI as a predictor of kidney failure in patients with C3G. The total chronicity score was the principal histologic correlate of kidney failure.

Treatment of C3 Glomerulopathy in Adult Kidney Transplant Recipients: A Systematic Review

BACKGROUND

C3 glomerulopathy (C3G), a rare glomerular disease mediated by alternative complement pathway dysregulation, is associated with a high rate of recurrence and graft loss after kidney transplantation (KTx). We aimed to assess the efficacy of different treatments for C3G recurrence after KTx.

METHODS

Databases (MEDLINE, EMBASE, and Cochrane Database) were searched from inception through 3 May, 2019. Studies were included that reported outcomes of adult KTx recipients with C3G. Effect estimates from individual studies were combined using the random-effects, generic inverse variance method of DerSimonian and Laird., The protocol for this meta-analysis is registered with PROSPERO (no. CRD42019125718).

RESULTS

Twelve studies (7 cohort studies and 5 case series) consisting of 122 KTx patients with C3G (73 C3 glomerulonephritis (C3GN) and 49 dense deposit disease (DDD)) were included. The pooled estimated rates of allograft loss among KTx patients with C3G were 33% (95% CI: 12-57%) after eculizumab, 42% (95% CI: 2-89%) after therapeutic plasma exchange (TPE), and 81% (95% CI: 50-100%) after rituximab. Subgroup analysis based on type of C3G was performed. Pooled estimated rates of allograft loss in C3GN KTx patients were 22% (95% CI: 5-46%) after eculizumab, 56% (95% CI: 6-100%) after TPE, and 70% (95% CI: 24-100%) after rituximab. Pooled estimated rates of allograft loss in DDD KTx patients were 53% (95% CI: 0-100%) after eculizumab. Data on allograft loss in DDD after TPE (1 case series, 0/2 (0%) allograft loss at 6 months) and rituximab (1 cohort, 3/3 (100%) allograft loss) were limited. Among 66 patients (38 C3GN, 28 DDD) who received no treatment (due to stable allograft function at presentation and/or clinical judgment of physicians), pooled estimated rates of allograft loss were 32% (95% CI: 7-64%) and 53% (95% CI: 28-77%) for C3GN and DDD, respectively. Among treated C3G patients, data on soluble membrane attack complex of complement (sMAC) were limited to patients treated with eculizumab (N = 7). 80% of patients with elevated sMAC before eculizumab responded to treatment. In addition, all patients who responded to eculizumab had normal sMAC levels after post-eculizumab.

CONCLUSIONS

Our study suggests that the lowest incidence of allograft loss (33%) among KTX patients with C3G are those treated with eculizumab. Among those who received no treatment for C3G due to stable allograft function, there is a high incidence of allograft loss of 32% in C3GN and 53% in DDD. sMAC level may help to select good responders to eculizumab.

Mycophenolate Mofetil in C3 Glomerulopathy and Pathogenic Drivers of the Disease

BACKGROUND AND OBJECTIVES

C3 glomerulopathy is a complement-mediated disease arising from abnormalities in complement genes and/or antibodies against complement components. Previous studies showed that treatment with corticosteroids plus mycophenolate mofetil (MMF) was associated with improved outcomes, although the genetic profile of these patients was not systematically analyzed. This study aims to analyze the main determinants of disease progression and response to this therapeutic regimen.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a retrospective, multicenter, observational cohort study in 35 nephrology departments belonging to the Spanish Group for the Study of Glomerular Diseases. Patients diagnosed with C3 glomerulopathy (n=81) or dense deposit disease (n=16) between January 1995 and March 2018 were enrolled. Multivariable and propensity score matching analyses were used to evaluate the association of clinical and genetic factors with response to treatment with corticosteroids and MMF as measured by proportion of patients with disease remission and kidney survival (status free of kidney failure).

RESULTS

The study group comprised 97 patients (84% C3 glomerulopathy, 16% dense deposit disease). Forty-two patients were treated with corticosteroids plus MMF, and this treatment was associated with a higher rate of remission and lower probability of kidney failure (79% and 14%, respectively) compared with patients treated with other immunosuppressives (24% and 59%, respectively), or ecluzimab (33% and 67%, respectively), or conservative management (18% and 65%, respectively). The therapeutic superiority of corticosteroids plus MMF was observed both in patients with complement abnormalities and with autoantibodies. However, patients with pathogenic variants in complement genes only achieved partial remission, whereas complete remissions were common among patients with autoantibody-mediated forms. The main determinant of no remission was baseline proteinuria. Relapses occurred after treatment discontinuation in 33% of the patients who had achieved remission with corticosteroids plus MMF, and a longer treatment length of MMF was associated with a lower risk of relapse.

CONCLUSIONS

The beneficial response to corticosteroids plus MMF treatment in C3 glomerulopathy appears independent of the pathogenic drivers analyzed in this study.

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.

Practical management of C3 glomerulopathy and Ig-mediated MPGN: facts and uncertainties

In recent years, a substantial body of experimental and clinical work has been devoted to C3 glomerulopathy and Ig-mediated membranoproliferative glomerulonephritis. Despite the rapid accumulation of data, several uncertainties about these 2 rare forms of nephropathies persist. They concern their pathophysiology, classification, clinical course, relevance of biomarkers and of pathology findings, and assessment of the efficacy of the available therapies. The present review discusses the impact of these uncertainties on the clinical management of patients.

Update on C3 Glomerulopathy: A Complement-Mediated Disease

C3 glomerulopathy (C3G) is a clinicopathologic entity secondary to dysregulation of the alternative complement pathway in plasma and the glomerular microenvironment. The current consensus definition of C3G relies on immunofluorescence staining criteria. However, due to its high clinical variability, these criteria may not be accurate enough in some clinical scenarios. Thus, a new pathogenic classification based on a cluster analysis of clinical, histologic, and genetic data has recently been proposed, which could also help identify patients at higher risk of progression. Several pathogenic abnormalities in complement genes have been described, and the role of autoantibodies in the disease is increasingly recognized, but still the genotype-phenotype correlations in C3G are poorly understood. C3G may be diagnosed in both children and adults. The spectrum of clinical manifestations is wide, although one of the most common clinical presentations is proteinuria with relatively preserved kidney function. In order to standardize the evaluation of kidney biopsies from these patients, a histopathologic index was recently proposed, including both parameters of activity and chronicity. However, this index has not yet been validated in independent cohorts. Currently, no targeted therapies are available in clinical settings for the treatment of C3G, although several new molecules are under investigation. Treatment with corticosteroids plus mycophenolate mofetil has been shown to be associated with improved renal outcomes, as compared to other immunosuppressive regimens. Yet, the main determinants of treatment response with this regimen and the influence of the underlying pathogenic drivers have not been extensively studied. The therapeutic response to eculizumab, an anti-C5 monoclonal antibody, has been shown to be highly heterogeneous. Thus, its current clinical indication in C3G is restricted to rapidly progressive forms of the disease. To summarize, in recent years, several important advances have taken place in the understanding of C3G, but still further studies are warranted to elucidate the best therapeutic strategies that could improve prognosis of this entity.

C3 Glomerulopathy: Pathogenesis and Treatment

C3 glomerulopathy (C3G) is a rare set of kidney diseases with 2 patterns: C3 glomerulonephritis (C3GN) and dense deposit disease. Pathogenesis of both diseases is due to complement dysregulation in the alternative pathway. Acquired or genetic alterations of the regulatory proteins of the complement pathway result in C3G. Although the disease is characterized by low C3 levels in serum and C3-dominant staining by immunofluorescence on biopsy, other disease entities such as infection-related glomerulonephritis and masked monoclonal deposits can present similarly. Both the C3GN and dense deposit disease variants of C3G are progressive and recur in transplanted kidneys. Although no direct treatment is available, complement blockers are either available or in the clinical trial phase. This review will survey the pathogenesis of C3GN and current treatment options.

Infection-related Glomerulonephritis and C3 Glomerulonephritis - Similar Yet Dissimilar: A Case Report and Brief Review of Current Literature

Infection-related glomerulonephritis (IRGN) is an immune complex-mediated glomerulonephritis (GN), often preceded by infection with subsequent recovery of renal function after the resolution of the infection. C3 deposition in the absence of immune complex deposits can be seen in patients with IRGN, but with the emergence of C3 glomerulonephritis (C3GN), the distinction is difficult as the clinical and pathological presentation may be similar. However, their treatment and clinical course vary significantly.

A 64-year-old man with a history of hypertension and bioprosthetic aortic valve presented to the Emergency Department with left upper quadrant (LUQ) pain and a purpuric rash on bilateral lower extremities. The patient became septic, and further workup during the hospitalization revealed endocarditis secondary to Streptococcus viridans. On admission, the patient had acute kidney injury (AKI) with a serum creatinine of 3.79 mg/dl, which peaked at 5.72 mg/dl during the hospitalization. Renal biopsy demonstrated segmental necrotizing glomerulonephritis on light microscopy, predominant C3 deposition on immunofluorescence (IF) staining, and mesangial and paramesangial deposits on electron microscopy. This histologic picture can be seen both in IRGN and C3GN. The patient was treated with intravenous ceftriaxone for six weeks for endocarditis and the kidney injury was managed with supportive care. The patient’s renal function improved and complement levels normalized, supporting the diagnosis of IRGN retrospectively. IRGN can mimic C3GN, and evaluation for alternate pathways of the complement system may be warranted in patients with atypical presentation of IRGN.

Anti-Factor B Antibodies and Acute Postinfectious GN in Children

BACKGROUND

The pathophysiology of the leading cause of pediatric acute nephritis, acute postinfectious GN, including mechanisms of the pathognomonic transient complement activation, remains uncertain. It shares clinicopathologic features with C3 glomerulopathy, a complement-mediated glomerulopathy that, unlike acute postinfectious GN, has a poor prognosis.

METHODS

This retrospective study investigated mechanisms of complement activation in 34 children with acute postinfectious GN and low C3 level at onset. We screened a panel of anticomplement protein autoantibodies, carried out related functional characterization, and compared results with those of 60 children from the National French Registry who had C3 glomerulopathy and persistent hypocomplementemia.

RESULTS

All children with acute postinfectious GN had activation of the alternative pathway of the complement system. At onset, autoantibodies targeting factor B (a component of the alternative pathway C3 convertase) were found in a significantly higher proportion of children with the disorder versus children with hypocomplementemic C3 glomerulopathy (31 of 34 [91%] versus 4 of 28 [14%], respectively). In acute postinfectious GN, anti-factor B autoantibodies were transient and correlated with plasma C3 and soluble C5b-9 levels. We demonstrated that anti-factor B antibodies enhance alternative pathway convertase activity in vitro, confirming their pathogenic effect. We also identified crucial antibody binding sites on factor B, including one correlated to disease severity.

CONCLUSIONS

These findings elucidate the pathophysiologic mechanisms underlying acute postinfectious GN by identifying anti-factor B autoantibodies as contributing factors in alternative complement pathway activation. At onset of a nephritic syndrome with low C3 level, screening for anti-factor B antibodies might help guide indications for kidney biopsy to avoid misdiagnosed chronic glomerulopathy, such as C3 glomerulopathy, and to help determine therapy.

Management and treatment of glomerular diseases (part 2): conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

In November 2017, the Kidney Disease: Improving Global Outcomes (KDIGO) initiative brought a diverse panel of experts in glomerular diseases together to discuss the 2012 KDIGO glomerulonephritis guideline in the context of new developments and insights that had occurred over the years since its publication. During this KDIGO Controversies Conference on Glomerular Diseases, the group examined data on disease pathogenesis, biomarkers, and treatments to identify areas of consensus and areas of controversy. This report summarizes the discussions on primary podocytopathies, lupus nephritis, anti-neutrophil cytoplasmic antibody-associated nephritis, complement-mediated kidney diseases, and monoclonal gammopathies of renal significance.

Therapeutic Modulation of the Complement System in Kidney Transplantation: Clinical Indications and Emerging Drug Leads

The complement system is integral to innate immunity, and it is an essential deterrent against infections. The complement apparatus comprises of >30 fluid-phase and surface-bound elements that also engage with the adaptive immune system, clear harmful immune complexes, and orchestrates several salutary physiological processes. An imbalance in the complement system's tightly regulated machinery and the consequent unrestrained complement activation underpins the pathogenesis of a wide array of inflammatory, autoimmune, neoplastic and degenerative disorders. Antibody-mediated rejection is a leading cause of graft failure in kidney transplantation. Complement-induced inflammation and endothelial injury have emerged as the primary mechanisms in the pathogenesis of this form of rejection. Researchers in the field of transplantation are now trying to define the role and efficacy of complement targeting agents in the prevention and treatment of rejection and other complement related conditions that lead to graft injury. Here, we detail the current clinical indications for complement therapeutics and the scope of existing and emerging therapies that target the complement system, focusing on kidney transplantation.

Usefulness of mycophenolate mofetil in Indian patients with C3 glomerulopathy

Background

C3 glomerulopathy (C3G) is a heterogeneous disease caused by alternative complement pathway abnormalities without any standardized treatment. An immunosuppressive agent, mycophenolate mofetil (MMF), has been recently shown to be useful in treating C3G, mainly in studies from the west. We report the clinical outcome of 17 Indian C3G patients treated with MMF with or without steroids.

Methods

The clinical and histology details of the C3G patients treated with MMF for at least 6 months with a follow-up of at least 12 months were retrieved from the medical records of our center.

Results

The median serum creatinine and proteinuria at presentation were 0.8 mg/dL and 3.7 g/day, respectively, with the majority (88.2%) presenting as nephrotic syndrome. The mean dose of MMF was 1.65 (±0.56) g/day, and the median duration of MMF therapy was 18 months. Two-thirds (64%) of the patients responded to the treatment, with complete remission in 4 (23%) and partial remission in 7 (41%) (median time: 9 months). Three patients progressed to end-stage renal disease (ESRD) on follow-up. Of the three patients, one (33%) had an initial response in proteinuria to MMF but did not respond after a relapse and subsequently progressed to ESRD and two (67%) other patients were nonresponsive to MMF from the start of the therapy.

Conclusion

Despite a small sample size and lack of a control arm, this study describes the effectiveness of MMF in treating C3G patients from Asia and forms a basis for future randomized trials.

C3 glomerulopathy - understanding a rare complement-driven renal disease

The C3 glomerulopathies are a group of rare kidney diseases characterized by complement dysregulation occurring in the fluid phase and in the glomerular microenvironment, which results in prominent complement C3 deposition in kidney biopsy samples. The two major subgroups of C3 glomerulopathy - dense deposit disease (DDD) and C3 glomerulonephritis (C3GN) - have overlapping clinical and pathological features suggestive of a disease continuum. Dysregulation of the complement alternative pathway is fundamental to the manifestations of C3 glomerulopathy, although terminal pathway dysregulation is also common. Disease is driven by acquired factors in most patients - namely, autoantibodies that target the C3 or C5 convertases. These autoantibodies drive complement dysregulation by increasing the half-life of these vital but normally short-lived enzymes. Genetic variation in complement-related genes is a less frequent cause. No disease-specific treatments are available, although immunosuppressive agents and terminal complement pathway blockers are helpful in some patients. Unfortunately, no treatment is universally effective or curative. In aggregate, the limited data on renal transplantation point to a high risk of disease recurrence (both DDD and C3GN) in allograft recipients. Clinical trials are underway to test the efficacy of several first-generation drugs that target the alternative complement pathway.

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.

C3 Glomerulopathy: Ten Years' Experience at Mayo Clinic

OBJECTIVE

To describe the clinicopathological features, complement abnormalities, triggers, treatment, and outcomes of C3 glomerulopathy.

PATIENTS AND METHODS

A total of 114 patients with C3 glomerulopathy seen at Mayo Clinic from January 1, 2007, through December 31, 2016, were evaluated in this study.

RESULTS

The mean age at diagnosis for the entire cohort was 40.4±22.3 years, with a median serum creatinine level and proteinuria value of 1.6 mg/dL (range: 0.3-14.7) (to convert to mmol/L, multiply by 0.0259) and 2605 mg/24 h (range: 233-24,165), respectively. Hematuria was present in 100 patients (87.7%). The C3 and C4 levels were low in 50 of 112 (44.6%) and 13 of 110 (11.8%) patients, respectively. A history of infection, positive autoimmune findings, and monoclonal gammopathy (MIg) were present in 33 of 114 (28.9%), 28 of 114 (24.6%), and 36 of 95 (37.9%) patients, respectively. However, 28 of 43 patients 50 years or older (65.1%) had MIg. A genetic variant in complement genes, C3 nephritic factor (C3Nef), and other autoantibodies was present in 26 of 70 (37.1%), 30 of 69 (43.5%), and 9 of 67 (13.4%) patients, respectively. Membranoproliferative and mesangial proliferative glomerulonephritis were the common patterns of injury. Patients without MIg were younger (mean age, 32.3±20.6 years), with a median serum creatinine level and proteinuria value of 1.4 mg/dL (range: 0.3-7.9) and 2450 mg/24 h (range: 250-24, 165) and with low C3 and C4 levels in 38 of 77 (49.4%) and 9 of 75 (12.0%) patients, respectively. Most patients received corticosteroids and other immunosuppressive drugs. In patients without MIg, at a median follow-up of 22.3 months (range: 0.1-201.1), the median serum creatinine level and proteinuria value were 1.4 mg/dL (range: 0.3-3.7) and 825.5 mg/24 h (range: 76-22, 603), and 7 patients (9.2%) had progression to end-stage renal disease.

CONCLUSION

C3 glomerulopathy is a heterogeneous disease entity with complex triggering events and abnormalities of the alternative pathway of complement. The disease tends to be progressive and exhibits a variable response to immunosuppressive therapy.