C3 glomerulonephritis and dense deposit disease share a similar disease course in a large United States cohort of patients with C3 glomerulopathy

Efficacy of complement inhibition with pegcetacoplan in children with C3 glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is a rare kidney disease due to a dysregulation of the alternative complement pathway, orphan of specific treatment. Pegcetacoplan is an inhibitor of the third complement component C3, currently on a phase III registration protocol in C3G. Here we describe our experience with the off-label use of pegcetacoplan in pediatric patients with C3G.

METHODS

This retrospective, observational study evaluated the efficacy and safety of pegcetacoplan in five pediatric patients, not eligible in the registration protocol, over a 12-week treatment period. The drug was given subcutaneously, twice a week for the first month, then weekly. The change in urinary protein-to-urinary creatinine ratio (mean of three samples) was the primary endpoint. We also evaluated the changes in serum C3, albumin, sC5-b9, creatinine, and urinary erythrocytes (number/µL).

RESULTS

At baseline, median proteinuria/creatininuria ratio (mean of three samples) was 4.97 mg/mg (3.53-7.69), and after 12 weeks of treatment with pegcetacoplan, it decreased to less than 30% of baseline (p = 0.043) as did erythrocyturia (p = 0.043). C3 levels increased more than 600% of baseline (p = 0.043), whereas the levels of sC5-b9 decreased to normal range (p = 0.043). Three of four patients with impaired kidney function showed an improvement in eGFR. No adverse event was recorded.

CONCLUSIONS

In C3G patients, pegcetacoplan therapy improves clinical and laboratory features during a 12-week treatment. The present study, although small and with a limited follow-up, supports the use of complement-targeted therapy in C3G. Further studies with a larger number of patients and longer follow-up are needed.

Acquired and genetic drivers of C3 and C5 convertase dysregulation in C3 glomerulopathy and immunoglobulin-associated MPGN

Dysregulation of the alternative pathway of complement plays a central role in the pathophysiology of C3 glomerulopathy (C3G). Various autoimmune and genetic factors targeting the alternative pathway have been associated with both C3G and primary immunoglobulin-associated membranoproliferative glomerulonephritis (Ig-MPGN), suggesting shared pathophysiological mechanisms. This review highlights the wide range of disease drivers identified that mainly target components or protein complexes of the alternative pathway, both in C3G and Ig-MPGN. Nephritic factors, which constitute a heterogeneous group of autoantibodies targeting the C3 or the C5 convertase, are the most common abnormalities. Monoclonal gammopathies are frequent in aging adults. They may promote complement activation and have in some cases also been found to target alternative pathway regulatory proteins. Additionally, some patients with C3G and Ig-MPGN carry rare variants in genes encoding complement activating or regulating proteins of the alternative pathway. This review provides an informative overview of pathogenetic mechanisms associated with each abnormality, acting at different steps in the complement cascade. The diversity of targets involved in the C3G pathophysiology suggests the potential benefit of therapeutical approaches tailored to the underlying disease drivers, with a pivotal impact upstream or at the level of the C3 or C5 convertase activity.

Pregnancy outcomes in C3 glomerulopathy: a retrospective review

BACKGROUND

C3 Glomerulopathy (C3G) is an ultra-rare glomerular disease driven by dysregulation of the alternative pathway of complement. 30-50% of adult patients progress to end stage kidney disease (ESKD) within 10 years of diagnosis. Little is known of the impact of pregnancy on the natural history of C3G or whether a coincident diagnosis of C3G affects maternal-fetal outcomes.

METHODS

Female subjects from the University of Iowa's C3G Natural History Study who met consensus biopsy criteria were included if they had at least one pregnancy and available renal/obstetric data. Assessed data included clinical history, kidney function tests, and complement tests to identify genetic and/or acquired drivers of complement dysregulation. Appropriate t-tests or z-tests were used to compare outcomes and clinical biomarker changes pre-/post-pregnancy. Nonlinear regression and relative risk were used to estimate risk for preeclampsia, premature delivery, and progression to ESKD.

RESULTS

Amongst mothers whose C3G presented before or during pregnancy (C3G + P), there were 37 pregnancies and 27 deliveries. Non-live birth outcomes impacted 10 C3G + P and included 5 spontaneous miscarriages, 1 stillbirth, 1 ectopic pregnancy, and 3 elective abortions. Twelve deliveries (44%) were premature, while 16 (59%) were associated with antepartum preeclampsia: an elevated risk when compared to healthy pregnancies and pregnancies of mothers with other glomerular diseases. Risk factors for complications included preexisting hypertension, an identified driver of complement dysregulation, and an eGFR prior to pregnancy of < 60 ml/min/1.73m2. These risk factors also predict progression to ESKD within 5 (5/32, 16%) and 10 years (6/32, 19%) following pregnancy. Compared to pre-pregnancy values, post-pregnancy serum creatinine levels trended upwards and eGFRs downwards, both by small but significant amounts. Individual pre-/post-pregnancy eGFRs were significantly worse in mothers who progressed to ESKD within 5-10 years of pregnancy.

CONCLUSIONS

A C3G + P is associated with increased risk of preeclampsia and prematurity compared to healthy controls, but no excess risk of spontaneous miscarriage. A C3G + P was associated with a small but significant decrease in renal function as measured by change in creatinine and eGFR. The elevated risk of adverse renal and obstetric events supports the need for multidisciplinary care for expectant patients with C3G.

Spatially resolved transcriptomic profiling for glomerular and tubulointerstitial gene expression in C3 glomerulopathy

Background

Complement 3 (C3) glomerulopathy (C3G) is a rare but clinically significant glomerulopathy. However, little is known about its transcriptomic profile. We investigated the substructure-specific gene expression profile of C3G using the recently introduced spatial transcriptomics technology.

Methods

We performed spatial transcriptomic profiling using GeoMx Digital Spatial Profiler with formalin-fixed paraffin-embedded kidney biopsy specimens of three C3G cases and seven controls from donor kidney biopsy. Additionally, 41 samples of other glomerulonephritis, including focal segmental glomerulosclerosis, membranous nephropathy and minimal change disease, were included as disease controls. We identified differentially expressed genes (DEGs) specific to C3G, followed by in vitro validation analysis of consistently upregulated DEGs in human glomerular endothelial cells through a co-culture with complement-stimulated macrophages.

Results

We found 229 and 157 highly expressed DEGs in the glomeruli of C3G compared with those of donor and disease controls, respectively, including POSTN, COL1A2 and IFI44L. Protease binding, structural molecule activity and extracellular matrix (ECM) structural constituent were among the top enriched Gene Ontology terms in the glomeruli of C3G. Specifically, genes related to the ECM and interferon activity were the most upregulated, with network analysis suggesting possible interactions between complement C3 and the ECM through CD11c. The in vitro experimental validation using iC3b-stimulated CD11c+ macrophages supported these findings, inducing elevated expression of fibrosis markers and ECM components in glomerular endothelial cells.

Conclusions

Significant disease-specific transcriptomic alterations in C3G, including upregulation of genes related to the ECM, provide potential insights into the pathophysiology.

Acquired and genetic determinants of disease phenotype and therapeutic strategies in C3 glomerulopathy and immunoglobulin-associated MPGN

C3 glomerulopathy (C3G), a prototype of complement-mediated disease, is characterized by significant heterogeneity, in terms of not only clinical, histological and biological presentation but also prognosis, and response to existing therapies. Recent advancements in understanding the factors responsible for alternative pathway dysregulation in the disease have highlighted its even more complex nature. Here, we propose a reexamination of the diversity of C3G presentations in light of the drivers of complement activation. Autoantibodies targeting complement proteins, genetic abnormalities in complement genes and monoclonal immunoglobulins are now well-known to drive disease occurrence. This review discusses how these drivers contribute to the heterogeneity in disease phenotype and outcomes, providing insights into tailored diagnostic and therapeutic approaches. In recent years, a broad spectrum of complement inhibitory therapies has emerged, soon to be available in clinical practice. The recognition of specific clinical, biological and histological patterns associated with different forms of C3G is crucial for personalized management, particularly treatment strategies.

Comparative Analysis of Proteinuria and Longitudinal Outcomes in Immune Complex Membranoproliferative Glomerulonephritis and C3 Glomerulopathy

Introduction

C3 glomerulopathy (C3G) and primary immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) are rare diseases that share a similar pathogenesis; however, the prognostic significance of proteinuria reduction remains poorly characterized. This study compared the outcomes in C3G and IC-MPGN and assessed the impact of changes in proteinuria on kidney prognosis.

Methods

This retrospective, longitudinal, multicenter study used joint linear mixed-effects models to assess proteinuria trajectories, and Cox regression to evaluate their association with kidney failure. In addition, time-averaged proteinuria (TA-P) was calculated to determine its impact on kidney prognosis.

Results

The study included 149 patients: 98 with C3G (66%) and 51 with IC-MPGN (34%) with a median age of 35 (interquartile range [IQR]: 22-53) years. During a median follow-up of 65 (IQR: 32-114) months, 44 patients (30%) progressed to kidney failure without differences across C3G or IC-MPGN. A strong association was observed between longitudinal increase in proteinuria and the risk of kidney failure. In addition, a ≥ 50% proteinuria reduction over time was associated with a lower risk of kidney failure (hazard ratio [HR]: 0.61; 95% confidence interval [CI]: 0.46-0.75, P < 0.001). Results were consistent in both C3G and IC-MPGN, and in those with baseline estimated glomerular filtration rate (eGFR) ≥ 30 ml/min per 1.73 m2 and proteinuria ≥ 1 g/d. A ≥30% proteinuria reduction at 6 months or a ≥50% proteinuria reduction at 12 months were associated with a slower eGFR decline. Patients were categorized into 4 subgroups based on TA-P levels, with TA-P values < 1 g/d indicating better kidney outcomes.

Conclusion

Proteinuria reduction was associated with improved kidney outcomes and slower eGFR decline in both C3G and IC-MPGN.

C3 glomerulopathy in children: experience at a resource-limited center

BACKGROUND

In children, C3 glomerulopathy (C3G) is a heterogeneous disease characterized by diverse clinicopathological profiles and kidney outcomes. However, diagnostic work-up in resource-limited settings is challenging because of the unavailability of complement assays and limited access to electron microscopy or genetic testing.

PURPOSE

This study aimed to describe the clinicopathological features and response to immunosuppression and evaluate renal outcomes among children with C3G in a resource-limited setting.

METHODS

This retrospective cohort study involved a review of the hospital records of 46 children (2013-2021) diagnosed with C3G on kidney biopsy. Their clinical, laboratory, treatment, and outcome details at onset and follow-up were noted.

RESULTS

The mean (standard deviation) age was 9 (4) years. The common presentation was acute nephritis (27 [58.6%]), while 1 in 5 (19.5%) presented with rapidly progressive glomerulonephritis. Focal crescentic glomerulonephritis (14 [30.4%]) was the common histological pattern. Electron microscopy was performed in 22 (47.8%), of which 17 were C3 glomerulonephritis and 4 were dense deposit disease (DDD). None of the patients underwent complement assay or genetic testing. Almost two-thirds (63%) received empirical immunosuppressive therapy, most commonly steroids. Of the 31/46 who completed follow-up (median [interquartile range] duration, 11.5 [6-24] months), 6 (19.4%) demonstrated complete kidney recovery, while the other 25 (80.7%) had kidney sequelae; of them, 5 (16.1%) progressed to end-stage kidney disease and 2 (4.3%) died by the last follow-up.

CONCLUSION

Pediatric C3G has a variable clinicopathological spectrum, while DDD is less common. Most patients present with glomerulonephritis and significant morbidities. The lack of genetic and C3Nephritic factor testing is a barrier to the comprehensive phenotyping and management of C3G in resource-limited settings.

C3 glomerulopathy in children: a European longitudinal study evaluating outcome

BACKGROUND

C3 glomerulopathy is a rare clinical entity characterized by dysregulation of the alternative complement pathway in glomerular disease. Studies defining the natural history of C3G in the pediatric population are scarce.

METHODS

Patients included in this retrospective study were diagnosed between 2011 and 2020 in 12 European pediatric nephrology units. Data were collected from baseline, 6 months, 12 months and at the last follow-up. Complete remission (CR) was defined as a urinary protein creatinine ratio (UPCR) < 0.3 mg/mg with normal estimated glomerular filtration rate (eGFR). Partial remission was defined as a decrease in UPCR to 0.3 and 3 mg/mg with normal eGFR. Lack of remission was defined as non-response.

RESULTS

A total of 108 pediatric patients were included. Complete remission was achieved in 71/108 patients (65.7%), with probability of CR of 50% at 1.8 years and of 78% at 7 years. At presentation by univariate analysis the predictive factors at presentation associated with CR included eGFR (p = 0.028), UPCR (p = 0.004), serum C3 levels (p = 0.018), elevated plasma sC5b9 levels, defined as > 400 ng/ml, (p = 0.037), the presence of endocapillary proliferation (p = 0.017), and the absence of dense deposits on electron microscopy (p = 0.032). By multivariate analysis a low UPCR at presentation (p < 0.001) and the presence of endocapillary proliferation (p < 0.01) remained positively associated with CR.

CONCLUSIONS

Our data confirm that C3G has a more benign outcome in children compared to previous reports in adults, and suggest that endocapillary proliferation and the degree of proteinuria at onset are the most relevant prognostic factors.

Safety and Efficacy of Avacopan in Patients with Complement 3 Glomerulopathy: Randomized, Double-Blind Clinical Trial

Background

Complement 3 (C3) glomerulopathy is a rare autoimmune disorder characterized by activation of the alternative complement pathway with isolated or dominant complement 3 deposition in glomeruli. Patients with C3 glomerulopathy may develop progressive deterioration in kidney function and kidney failure.

Methods

We studied the safety and efficacy of avacopan 30 mg twice daily in patients with C3 glomerulopathy (N=57) with elevated (>244 ng/ml) and normal (≤244 ng/ml) levels of membrane attack complex or terminal complement complex (C5b-9) in a randomized, double-blind, placebo-controlled, phase 2 trial, with kidney biopsies performed prerandomization and at 26 and 52 weeks. The primary outcome was the percent change from baseline to week 26 in C3 Glomerulopathy Histological Index for disease activity.

Results

The study was conducted in patients with C3 glomerulopathy, including C3 GN and dense deposit disease. The median study duration was 60.0 weeks (interquartile range, 59.9–61.0). There were no significant differences in the primary outcome between the avacopan and the placebo group—least squares mean treatment difference (95% confidence interval)= −0.0 (−1.9 to 1.8). The secondary measures of efficacy including C3 Glomerulopathy Histological Index for disease chronicity, urine protein:creatinine ratio, and eGFR were not different between treatment groups. The overall incidence and type of adverse events for both treatment groups were comparable. No deaths were reported during the study, and no new safety signals were detected.

Conclusions

The primary end point for the study was not met; other clinical effects of avacopan to improve certain key kidney function parameters and slow disease progression were variable and require further evaluation.

Pegcetacoplan for the Treatment of Paediatric C3 Glomerulonephritis: A Case Report

Complement 3 glomerulonephritis (C3GN) is a rare glomerular disease involving dysregulation of the complement system. We describe our experience using pegcetacoplan, an inhibitor of C3 and its activation fragment, C3b, for treatment-resistant C3GN in a 9-year-old boy referred for evaluation of refractory membranoproliferative glomerulonephritis. Despite treatment with intense immunosuppression (high-dose steroids, mycophenolate mofetil and calcineurin inhibitor), he continued to have high disease activity with low C3 levels (35 mg/dL), hypertension, symptomatic oedema, anaemia, and nephrotic-range proteinuria (e.g., urine protein-to-creatinine ratio [uPCR], 10 g/g; serum creatinine, 0.4 mg/dL). Given the concern for refractory C3GN following a steroid taper and tacrolimus trial with modest response (reduced proteinuria), we initiated pegcetacoplan 540 mg twice weekly for 1 week, followed by 648 mg twice weekly. Laboratory values before pegcetacoplan initiation included uPCR, 1.1 g/g, serum creatinine, 0.87 mg/dL, serum albumin, 4.7 g/dL, and serum C3, 30 mg/dL. Clinically significant improvements in serum C3 (142 mg/dL) and uPCR (422 mg/g) were observed within 1 week of pegcetacoplan initiation; within 3 months (uPCR, 322 mg/g; serum creatinine, 0.69 mg/dL; serum C3, 297 mg/dL), all immunosuppressive and antihypertensive medications were discontinued. No adverse effects of pegcetacoplan were reported. A kidney biopsy after 6 months of pegcetacoplan treatment showed mesangial and focal endocapillary proliferative glomerulonephritis with isolated C3c deposition by immunofluorescence, consistent with previous C3GN diagnosis. In this paediatric patient, compassionate use of pegcetacoplan was associated with rapid clinical improvement without adverse effects, and clinical effectiveness was confirmed by laboratory and histologic results within 6 months of treatment initiation.

Iptacopan Reduces Proteinuria and Stabilizes Kidney Function in C3 Glomerulopathy

Introduction

C3 glomerulopathy (C3G) is a complex, chronic, ultra rare, progressive primary glomerulonephritis, resulting from alternative complement pathway overactivation, leading to kidney failure in most patients, and frequent recurrence in transplants. Iptacopan (LNP023) is an oral, proximal complement inhibitor specifically targeting factor B, that selectively inhibits the alternative complement pathway.

Methods

This was a phase 2 extension study of 26 adult patients with native kidney (cohort A), or recurrent C3G (post kidney transplantation; cohort B) receiving open label iptacopan.

Results

At 12 months, patients in cohort A had a significant reduction in 24-hour urine protein-to-creatinine ratio (UPCR; 57%; P < 0.0001; confidence interval [CI]: 0.31-0.59), an improvement in estimated glomerular filtration rate (eGFR; 6.83 ml/min per 1.73 m2; P = 0.0174; CI: 1.25-12.40), and an increase in serum C3 levels (geometric mean ratio to baseline: 3.53; P < 0.0001; CI: 3.01-4.15). In cohort B, most patients had normal urinary protein excretion at baseline (mean [range] 24-hour UPCR: 121 [9-445]), which was slightly lower by 12 months (21% reduction; CI: 0.48-1.31; P = 0.3151). In cohort B at 12 months, mean eGFR was at baseline values (mean change from baseline: -0.96 ml/min per 1.73 m2; P = 0.7335; CI: -6.60 to 4.69). Cohort B patients had significantly higher serum C3 values at 12 months compared with baseline (ratio:1.96; CI: 1.70-2.27; P < 0.0001). In cohorts A + B combined, the median difference in C3 deposit score on renal biopsy from baseline was -7.00 (CI: -12.00 to 4.00;) at 9 to 12 months treatment with iptacopan.

Conclusion

These data provide a clinical rationale for further evaluation of long-term treatment of C3G with iptacopan.

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.

Clinical and Pathological Course of Recurrent C3 Glomerulonephritis from Onset to Graft Loss: A Case Report

Introduction

Complement 3 glomerulonephritis (C3GN) has a high recurrence rate after kidney transplantation. Before the disease became well understood, kidney transplantation was performed without a diagnosis of C3GN. This report describes a case of recurrent C3GN diagnosed using allograft biopsy and evaluates its long-term clinical and pathological course.

Case Presentation

A 35-year-old man with membranoproliferative glomerulonephritis underwent an ABO-compatible living-donor renal transplantation. Three weeks post-transplantation, an allograft biopsy showed prominent granular C3 deposits. One year after transplantation, an allograft biopsy revealed slight mesangial expansion with C3 deposits and a few urinary proteins. Recurrent C3GN was diagnosed based on similar C3 deposition in the native kidney. Eight years post-transplantation, urinary protein levels began to increase and renal function gradually declined. Approximately 10 years after transplantation, an allograft biopsy revealed severe secondary focal segmental glomerulosclerosis and arteriolopathy with no active C3GN lesions. Ten months later, deteriorating kidney function necessitated hemodialysis.

Conclusion

In this case, C3GN recurred early after transplantation, but its activity did not increase for 8 years. The causes of chronic allograft dysfunction vary among cases. More cases and detailed observational studies are needed to determine treatment strategies for recurrent C3GN and graft prognosis.

Efficacy and Safety of Pegcetacoplan in Kidney Transplant Recipients With Recurrent Complement 3 Glomerulopathy or Primary Immune Complex Membranoproliferative Glomerulonephritis

Introduction

Complement 3 glomerulopathy (C3G) and primary immune complex membranoproliferative glomerulonephritis (IC-MPGN) have high risks for disease recurrence and allograft loss in transplant kidneys. Pegcetacoplan (targeted complement 3 [C3]/C3b inhibitor) may prevent excessive deposition of C3 and complement 5 [C5] breakdown products and associated renal damage.

Methods

NOBLE (NCT04572854) is a prospective, phase 2, multicenter, open-label, randomized controlled trial evaluating the efficacy and safety of pegcetacoplan in posttransplant patients with recurrent C3G or IC-MPGN. The primary end point was reduction in C3c staining on renal biopsy at week 12 for patients who received either pegcetacoplan 1080 mg twice weekly by subcutaneous infusion plus standard-of-care (SOC) or SOC only.

Results

Ten patients received pegcetacoplan and 3 received SOC only through week 12. At week 12, 5 of 10 pegcetacoplan-treated patients (50%) achieved ≥2 orders of magnitude (OOM) reduction in C3 staining (4 of these 5 had 0 staining and absent electron microscopy deposits) and 8 of 10 (80%) achieved ≥1 OOM reduction; 1 of 3 (33%) SOC-only patients showed staining reduction. Mean C3G histology activity score decreased by >54% in 8 of 10 pegcetacoplan-treated patients (80.0%). Pegcetacoplan-treated patients with baseline urine protein-to-creatinine ratio (uPCR) ≥1000 mg/g showed a median (interquartile range [IQR]) 54.4% (-56.33 to -53.95) reduction in proteinuria at week 12. In addition, pegcetacoplan-treated patients showed stable estimated glomerular filtration rate (eGFR), reduced plasma sC5b-9, and increased serum C3. Pegcetacoplan was well-tolerated and most adverse events were mild/moderate. No discontinuations, treatment withdrawals, or deaths were reported.

Conclusion

NOBLE demonstrated efficacy, safety, and tolerability of pegcetacoplan for patients with posttransplant recurrent C3G and primary IC-MPGN.

Establishing the Future Direction of Clinical Outcomes in C3 Glomerulopathy: Perspectives From a Patient and a Physician

Complement 3 glomerulopathy (C3G) is an ultra-rare glomerulonephritis caused by dysregulation of the alternative complement pathway. C3G has an estimated incidence of 1-3 cases per million people in the United States. Diagnosing C3G based solely on clinical and laboratory features is challenging because it mimics several other glomerular diseases; therefore, diagnosis requires a kidney biopsy. In the absence of disease-modifying therapies and optimal patient management strategies, C3G poses a significant physical and emotional burden on patients and caregivers. Common symptoms of glomerulonephritis include fatigue, edema, anxiety, and/or depression, which have profound effects on patients' daily lives. Approximately half of all patients progress to kidney failure within 10 years of diagnosis. Encouragingly, the treatment landscape in C3G is poised to change, with several targeted complement inhibitors in late-stage development. This perspectives article explores a patient's journey in C3G and discusses the current and future status of clinical outcomes and patient management from the viewpoints of a practicing nephrologist and a patient.

Gene variant C3 glomerulonephritis with chronic urinary tract infection: A case report and literature review

RATIONALE

C3 glomerulonephritis (C3GN) is 1 type of C3 nephropathy which is a rare glomerular disease associated with abnormal regulation of the alternative complement pathway. This review reports a rare case of C3GN with repeated urinary tract infection and summarizes the clinical features, differential diagnosis, treatment, and outcome of patients with C3GN.

PATIENT CONCERNS

A 44-year-old woman was admitted to our hospital because of proteinuria increased for more than 8 years.

DIAGNOSES

The patient was finally diagnosed with C3GN by renal biopsy and gene testing.

INTERVENTIONS

The patient was worried about the side effects of drugs and strongly refused to use glucocorticoids and immunosuppressants, so she was given angiotensin II receptor blocker monotherapy for glomerulonephritis and quinolones for urinary tract infection.

OUTCOMES

Serum creatinine, proteinuria, and serum complement c3 levels remained stable. Our case is still under continuous follow-up.

LESSONS

Clinical diagnosis of C3GN is difficult to make as there are many differential diagnoses, especially post infection nephritis. This case emphasizes the importance of renal biopsy in the diagnosis of C3GN, but the relationship between gram-negative bacilli and C3GN is still unclear. In addition, gene mutation is also involved in the pathogenesis of C3GN, and the treatment of C3GN still needs to be explored.

The Difficulties of Treating Complement-3-Mediated Glomerulopathy

BACKGROUND

C3 glomerulopathy (C3G) is a rare disease affecting the complement alternative pathway, categorized into dense deposit disease and C3 glomerulonephritis. Dense deposit disease predominantly affects younger individuals, while C3 glomerulonephritis tends to manifest in older populations. The diseases are characterized by dysregulation of the complement alternative pathway, leading to the deposition of complement components in the glomeruli and subsequent renal dysfunction. Notably, the incidence of C3G in the United States is low, with 1-3 cases per 1,000,000 and a prevalence of 5 cases per 1,000,000.

AREAS OF UNCERTAINTY

Numerous uncertainties persist in comprehending the etiology and pathophysiology of C3G. While biomarkers such as C3 nephritic factor, autoantibodies, and relevant genetic mutations have been identified, their pathogenicity and clinical utility remain unclear. Standard workups involve complement assays and autoantibody panels, yet the definitive diagnostic test remains a kidney biopsy. Nuanced challenges lie in deciphering the sensitivity and specificity of these diagnostic tools, especially in the presence of phenotypical variations among individuals.

THERAPEUTIC ADVANCEMENT

Current therapeutic approaches, albeit lacking robust evidence, encompass a spectrum ranging from supportive care to targeted B-cell therapy and immunosuppression with mycophenolate mofetil and glucocorticoids. For severe and refractory cases, the monoclonal antibody eculizumab, targeting C5 in the complement cascade, is recommended. These treatments, while offering some relief, pose challenges related to their cost and obtaining insurance approval. Exploratory avenues delve into the potential of plasma exchange and innovative treatments such as oral complement inhibitors, reflecting the ongoing quest for effective therapeutic modalities. Trials investigating various complement inhibitors underscore the dynamic landscape of therapeutic advancements in C3G management.

CONCLUSION

In conclusion, the article highlights the complexities of C3G management. The need for further understanding, large-scale trials, and ongoing investigations into disease etiology and pathophysiology is emphasized.

Clinicopathological characteristics and outcomes of adult patients with idiopathic membranoproliferative glomerulonephritis according to an immunofluorescence-based classification

BACKGROUND

The classification of membranoproliferative glomerulonephritis (MPGN) into immune complex-mediated MPGN and complement-mediated MPGN on immunofluorescence has provided insights into two distinct disease processes. There are limited data available on renal outcomes of MPGN from developing countries.

METHODS

A retrospective analysis was conducted on biopsy-proven MPGN cases diagnosed between 1998 and 2018 at the Sindh Institute of Urology and Transplantation (SIUT). Secondary causes were excluded. Patients were reclassified as immune complex-mediated-MPGN and complement-mediated-MPGN based on immunofluorescence results. The clinicopathological findings and outcomes of the two groups were compared.

RESULTS

In total, 213 patients with idiopathic MPGN were identified. Among these, 163 (76.5%) were reclassified as immune complex-mediated-MPGN and 50 (23.4%) as complement-mediated-MPGN. No significant differences were found between the two groups regarding age, gender, clinical characteristics, biopsy indications, biopsy findings, and renal function at presentation. Overall, 63 subjects (38.7%) with immune complex-mediated-MPGN and 27 (54%) with complement-mediated-MPGN received immunosuppressive agents (p = 0.08). Complete and partial remission rates were higher in immune complex-mediated-MPGN than in complement-mediated-MPGN (76% vs 58%, p < 0.05). At two years, median estimated glomerualr filtration rate (eGFR) tended to be higher in patients with immune complex-mediated-MPGN 91.2 (45.4-113.7) vs 83.45(34.6-102.50) ml/min/1.73 m2, p = 0.22) with significantly better renal survival (76% vs 58%, p = 0.03). Comparatively, more patients progressed to end-stage kidney disease (ESKD) in the complement-mediated-MPGN group (32% vs 19.6%, p = 0.06), with increased overall mortality (5 (10%) vs 7 (4.3%), p = 0.12).

CONCLUSION

The clinicopathological features at presentation of complement-mediated-MPGN are similar to those of immune complex-mediated-MPGN. However, it is less frequent and overall prognosis is less favorable.

The role of complement in kidney disease: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Uncontrolled complement activation can cause or contribute to glomerular injury in multiple kidney diseases. Although complement activation plays a causal role in atypical hemolytic uremic syndrome and C3 glomerulopathy, over the past decade, a rapidly accumulating body of evidence has shown a role for complement activation in multiple other kidney diseases, including diabetic nephropathy and several glomerulonephritides. The number of available complement inhibitor therapies has also increased during the same period. In 2022, Kidney Diseases: Improving Global Outcomes (KDIGO) convened a Controversies Conference, "The Role of Complement in Kidney Disease," to address the expanding role of complement dysregulation in the pathophysiology, diagnosis, and management of various glomerular diseases, diabetic nephropathy, and other forms of hemolytic uremic syndrome. Conference participants reviewed the evidence for complement playing a primary causal or secondary role in progression for several disease states and considered how evidence of complement involvement might inform management. Participating patients with various complement-mediated diseases and caregivers described concerns related to life planning, implications surrounding genetic testing, and the need for inclusive implementation of effective novel therapies into clinical practice. The value of biomarkers in monitoring disease course and the role of the glomerular microenvironment in complement response were examined, and key gaps in knowledge and research priorities were identified.

Developing Therapies for C3 Glomerulopathy: Report of the Kidney Health Initiative C3 Glomerulopathy Trial Endpoints Work Group

Randomized clinical trials are underway to evaluate the efficacy of novel agents targeting the alternative complement pathway in patients with C3 glomerulopathy (C3G), a rare glomerular disease. The Kidney Health Initiative convened a panel of experts in C3G to ( 1 ) assess the data supporting the use of the prespecified trial end points as measures of clinical benefit and ( 2 ) opine on efficacy findings they would consider compelling as treatment(s) of C3G in native kidneys. Two subpanels of the C3G Trial Endpoints Work Group reviewed the available evidence and uncertainties for the association between the three prespecified end points-( 1 ) proteinuria, ( 2 ) eGFR, and ( 3 ) histopathology-and anticipated outcomes. The full work group provided feedback on the summaries provided by the subpanels and on what potential treatment effects on the proposed end points they would consider compelling to support evidence of an investigational product's effectiveness for treating C3G. Members of the full work group agreed with the characterization of the data, evidence, and uncertainties, supporting the end points. Given the limitations of the available data, the work group was unable to define a minimum threshold for change in any of the end points that might be considered clinically meaningful. The work group concluded that a favorable treatment effect on all three end points would provide convincing evidence of efficacy in the setting of a therapy that targeted the complement pathway. A therapy might be considered effective in the absence of complete alignment in all three end points if there was meaningful lowering of proteinuria and stabilization or improvement in eGFR. The panel unanimously supported efforts to foster data sharing between academic and industry partners to address the gaps in the current knowledge identified by the review of the end points in the aforementioned trials.

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.

Prognostic factors and validation of the histologic chronicity score for C3 glomerulopathy: a registry analysis

Background

Data on the prognostic factors for C3 glomerulopathy (C3G) are limited, and validation of the new C3G histologic index (C3G-HI) in different settings is still needed. We aimed to evaluate the chronicity score of C3G-HI and probable prognostic factors in our population.

Methods

In this registry study, 74 patients from 20 centers with adequate follow-up data were included. Total chronicity score (TCS) was calculated according to percentages of glomerulosclerosis, interstitial fibrosis, tubular atrophy, and presence of arterio- and arteriolosclerosis. Primary composite outcome was defined as doubling of serum creatinine from baseline, undergoing dialysis or transplantation, development of stage 5 chronic kidney disease, or death.

Results

Median age was 34 [interquartile range (IQR) 24-46] years, and 39 patients (52.7%) were male. Median follow-up duration was 36 (IQR 12-60) months, and median TCS was 3 (IQR 1-5). Overall, 19 patients (25.7%) experienced primary composite outcome. Multivariate Cox regression model showed that only hemoglobin [adjusted HR (aHR) 0.67, 95% confidence interval 0.46-0.97, P = .035] predicted primary composite outcome, and TCS fell short of the statistical significance (aHR 1.26, 0.97-1.64, P = .08). Receiver operating characteristic analysis demonstrated that TCS showed an area under the curve value of 0.68 (0.56-0.78, P = .028) in discriminating primary composite outcome at 3 years, and 3-year kidney survival was lower in patients with TCS ≥4 (72.4%) compared with TCS <4 (91.1%) in Kaplan-Meier analysis (P = .036).

Conclusions

Low hemoglobin levels predicted dismal outcomes in patients with C3G. TCS ≥4 was associated with a worse 3-year kidney survival, which validated the 3-year prognostic value of the TCS of C3G-HI in our population.

Complement Terminal Pathway Activation and Intrarenal Immune Response in C3 Glomerulopathy

Key Points

Background

C3 glomerulopathy is a rare disease resulting from an overactivation of the complement alternative pathway. Although there is also evidence of terminal pathway activation, its occurrence and consequences on the disease have been poorly studied.

Methods

We retrospectively studied a cohort of 42 patients diagnosed with C3 glomerulopathy. We performed centralized extensive characterization of histological parameters. Kidney C5b-9 staining was performed as a marker of terminal pathway activation; intrarenal immune response was characterized through transcriptomic analysis.

Results

Eighty-eight percent of biopsies showed C5b-9 deposits in glomeruli. Biopsies were grouped according to the amount of C5b-9 deposits (no or low n=15/42, 36%; intermediate n=15/42, 36%; and high n=12/42, 28%). Patients with high C5b-9 deposits significantly differed from the two other groups of patients and were characterized by a significant higher histological chronicity score (P = 0.005) and lower outcome-free survival (P = 0.001). In multivariable analysis, higher glomerular C5b-9 remained associated with poor kidney prognosis after adjustment. One third of the 847 studied immune genes were upregulated in C3 glomerulopathy biopsies compared with controls. Unsupervised clustering on differentially expressed genes identified a group of kidney biopsies enriched in high glomerular C5b-9 with high immune and fibroblastic signature and showed high chronicity scores on histological examination.

Conclusions

In a cohort of patients with C3 glomerulopathy, intrarenal terminal pathway activation was associated with specific histological phenotype and disease prognosis.

Apical tubular complement activation and the loss of kidney function in proteinuric kidney diseases

Many kidney diseases are associated with proteinuria. Since proteinuria is independently associated with kidney function loss, anti-proteinuric medication, often in combination with dietary salt restriction, comprises a major cornerstone in the prevention of progressive kidney failure. Nevertheless, complete remission of proteinuria is very difficult to achieve, and most patients with persistent proteinuria slowly progress toward kidney failure. It is well-recognized that proteinuria leads to kidney inflammation and fibrosis via various mechanisms. Among others, complement activation at the apical side of the proximal tubular epithelial cells is suggested to play a crucial role as a cause of progressive loss of kidney function. However, hitherto limited attention is given to the pathophysiological role of tubular complement activation relative to glomerular complement activation. This review aims to summarize the evidence for tubular epithelial complement activation in proteinuric kidney diseases in relation to loss of kidney function.

C3 Glomerulopathy Recurs Early after Kidney Transplantation in Serial Biopsies Performed within the First 2 Years after Transplantation

Background

C3 glomerulopathy (C3G), which encompasses C3GN and dense deposit disease (DDD), results from dysregulation of the alternative complement pathway. Data on disease recurrence after kidney transplantation are limited, and details on histologic features of recurrent C3G are scarce. We aimed to evaluate C3G recurrence in the allograft, with a focus on histologic presentation and progression.

Methods

We retrospectively analyzed 18 patients with native kidney failure attributed to C3G (12 C3GN and six DDD), who received a kidney transplant from January 2016 to January 2023. Demographic, genetic, clinical, and histologic data were studied. The NanoString 770 genes PanCancer Immune Profiling Panel was used for transcriptomic analysis. Disease recurrence was the primary outcome.

Results

During a median (interquartile range) follow-up period of 37 (18–56) months, C3G recurrence occurred in 16 (89%) patients (11 with C3GN and five with DDD) at a median (interquartile range) of 33 (13–141) days after transplantation. Over a third (38%) of recurrent cases were detected in protocol biopsies, and only 31% of patients presented with >300 mg/g of proteinuria. Recurrence in index biopsies was mainly established through a combination of immunofluorescence and electron microscopy findings, while it showed only subtle histologic alterations and no characteristic transcriptomic signals. Over time, histologic chronicity indices increased, but all the allografts were functioning at the end of follow-up. Patients with recurrence of C3GN and DDD showed overlapping immunofluorescence and electron microscopy findings and had similar recurrence rate and time to recurrence.

Conclusions

Most of the patients with native kidney failure attributed to C3G developed disease recurrence very early after kidney transplantation, usually with minimal proteinuria, mild histologic alterations, and favorable short-term allograft survival. Immunofluorescence and electron microscopy played a crucial role in detecting early, subclinical recurrence of C3GN and DDD, which showed significant overlapping features.

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.

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.

Update on C3 Glomerulopathy

C3 glomerulopathy (C3G) is a rare disorder marked by deposition of C3 in the glomerulus, resulting in damage to the glomerular filtration unit and presenting with features of the nephritic and nephrotic syndromes. Fundamentally, C3G is caused by dysregulation of the alternative pathway of the complement cascade, either due to genetic variants or acquired humoral factors. Despite significant advances in recent years in the understanding of the underlying mechanisms and culprit lesions that result in the development of C3G, treatment options remain severely limited, and the prognosis is often poor. Fortunately, a number of anticomplement therapies are emerging from the drug development pipeline, with several in late-stage testing in patients with C3G, and there is hope that we will soon have more targeted options for managing patients with this devastating disease. In this review, we provide an overview of C3G, as well as summarizing the evidence for current treatments and detailing the clinical trials that are currently underway.

Significance of the total renal chronicity score in predicting renal outcome in PLA2R-associated membranous nephropathy

BACKGROUND

Phospholipase A2 receptor (PLA2R)-associated membranous nephropathy accounts for the majority of membranous nephropathy; however, few studies have determined the prognostic impact and clinical application of renal pathologic change on this disease.

METHODS

A retrospective cohort study of 262 patients with PLA2R-associated membranous nephropathy was conducted. The total renal chronicity score calculated according to the degree of glomerulosclerosis, interstitial fibrosis, tubular atrophy, and arteriosclerosis was applied to evaluate renal chronicity. Baseline bias was adjusted by inverse probability weight when assessing the prognostic impact of chronicity, and multiple parameters were used to evaluate the application value of renal chronicity.

RESULTS

During a median follow-up of 24.5 months, renal outcome (kidney function deterioration and/or end-stage kidney disease) was observed in 22 (8.40%) patients. Not only did a higher total renal chronicity score independently predict renal outcome [odds ratio (OR): 1.562, 95% confidence interval (CI) 1.073-2.273, P = 0.020], but non-minimal chronicity was also an independent risk factor for renal outcome (OR: 3.170, 95% CI 1.040-9.659, P = 0.042). Moreover, the membranous nephropathy risk classification in the Kidney Disease: Improving Global Outcomes (KDIGO) guideline integrated with non-minimal chronicity showed improvements in categorical net reclassification (0.174, 95% CI 0.012-0.335, P = 0.035), continuous net reclassification (0.462, 95% CI 0.087-0.838, P = 0.016), and integrated discrimination (0.019, 95% CI 0.003-0.035, P = 0.020) compared to the original classification.

CONCLUSIONS

Renal chronicity is closely associated with renal outcomes in PLA2R-associated membranous nephropathy, and combining the KDIGO risk classification with chronicity scores may provide a more accurate prognostic prediction.

From inflammation to renal fibrosis: A one-way road in autoimmunity?

Renal fibrosis is now recognized as a main determinant of renal pathology to include chronic kidney disease. Deposition of pathological matrix in the walls of glomerular capillaries, the interstitial space, and around arterioles predicts and contributes to the functional demise of the nephron and its surrounding vasculature. The recent identification of the major cell populations of fibroblast precursors in the kidney interstitium such as pericytes and tissue-resident mesenchymal stem cells, or bone-marrow-derived macrophages, and in the glomerulus such as podocytes, parietal epithelial and mesangial cells, has enabled the study of the fibrogenic process thought the lens of involved immunological pathways. Besides, a growing body of evidence is supporting the role of the lymphatic system in modulating the immunological response potentially leading to inflammation and ultimately renal damage. These notions have moved our understanding of renal fibrosis to be recognized as a clinical entity and new main player in autoimmunity, impacting directly the management of patients.

Morphological and etiological analyses of C3 and non-C3 glomerulonephritis in primary membranoproliferative glomerulonephritis using periodic acid-methenamine silver stain electron microscopy: a retrospective multicentered study

This study elucidated the etiology of C3 glomerulonephritis (C3GN) and non-C3GN with primary membranoproliferative glomerulonephritis (MPGN) using transmission electron microscopy (TEM) and periodic acid-methenamine silver stain (PAM-EM). Thirty-one primary MPGN cases were analyzed by TEM and PAM-EM to distinguish among MPGN I, MPGN II, MPGN III Burkholder subtype (MPGN IIIB), and Anders and Strife subtype (MPGN IIIA/S). Each case was also classified into C3GN or non-C3GN according to the standard C3GN definition using immunostaining. Four cases of MPGN II met C3 glomerulopathy; whereas, four cases of MPGN IIIB did not meet C3 glomerulopathy. Seven of 11 cases (64%) of MPGN I without GBM disruption and 7 of 12 cases (58%) of MPGN IIIA/S with GBM disruption met the non-C3GN criteria with significant immunoglobulins' deposition. Regardless of the C3GN or non-C3GN diagnosis, the deposits in primary MPGN I and MPGN IIIA/S exhibited ill-defined, amorphous, and foggy characteristics similar to those found in postinfectious GN but were different from immune complex (IC) deposits seen in MPGN IIIB. Not only C3GN but also non-C3GN was due to mechanisms other than IC deposition as found in postinfectious GN. Consequently, GBM disruption of MPGN IIIA/S was not due to IC deposition.

The relationship between histopathological features, immunosuppression and outcome in patients undergoing native kidney biopsies

AIMS

To assess retrospectively the association between histopathological lesions on renal biopsy and subsequent impairment of renal function across the spectrum of kidney diseases and to explore the influence of immunosuppressive therapy within the first 6 months after biopsy on this association.

METHODS AND RESULTS

Clinical data from 488 adult patients having a renal biopsy reported at a single centre from 2017 to 2019 were obtained during a median follow-up period of 786 days. Seventeen semi-quantitative histology parameters were recorded at the time of biopsy, 14 of which were suitable for assessment of association with loss of eGFR by multivariable Cox regression analysis, measurement of eGFR slope and measurement of eGFR 12 months after biopsy. A widely used histopathological chronicity score was also assessed. Clinical baseline variables including prescription of immunosuppression were recorded. Seven of 14 histology parameters: mesangial matrix expansion, global glomerulosclerosis, tubular atrophy, interstitial fibrosis, arteriolosclerosis, mesangial hypercellularity and acute tubular injury; and the chronicity score, predicted loss of kidney function by all three measures. Prescription of immunosuppression was more likely in patients with active inflammatory pathology and less likely in patients with chronic fibrotic pathology, and was associated with reduced risk of loss of eGFR.

CONCLUSIONS

This retrospective study demonstrates the prognostic significance and complex relationship with immunosuppression of routinely reported histopathological variables in patients having native kidney biopsies, across the spectrum of kidney diseases. It provides useful information for renal biopsy prognostication and design of retrospective studies, including machine learning models.

Complement Activation in Nephrotic Glomerular Diseases

The nephrotic syndrome holds significant clinical importance and is characterized by a substantial protein loss in the urine. Damage to the glomerular basement membrane or podocytes frequently underlies renal protein loss. There is an increasing belief in the involvement of the complement system, a part of the innate immune system, in these conditions. Understanding the interactions between the complement system and glomerular structures continually evolves, challenging the traditional view of the blood-urine barrier as a passive filter. Clinical studies suggest that a precise inhibition of the complement system at various points may soon become feasible. However, a thorough understanding of current knowledge is imperative for planning future therapies in nephrotic glomerular diseases such as membranous glomerulopathy, membranoproliferative glomerulonephritis, lupus nephritis, focal segmental glomerulosclerosis, and minimal change disease. This review provides an overview of the complement system, its interactions with glomerular structures, and insights into specific glomerular diseases exhibiting a nephrotic course. Additionally, we explore new diagnostic tools and future therapeutic approaches.

A Case of C3 Nephritis With a Rare Variant of the CFHR5 Gene

C3 nephropathy is a renal disease caused by the aberrant activation of the alternative complement pathway. The long-term renal prognosis of C3 nephropathy is generally poor, and elucidation of its pathogenesis is clinically important. Genetic abnormalities within complement genes, encompassing autoantibodies targeting complement components and complement factor H-related proteins (CFHRs), can lead to abnormal complement activation. CFHR5 is one of the best-known responsible genes for C3 nephritis. Moreover, the renal prognosis can vary depending on the specific type of genetic mutation. Here, we report the case of a young woman with C3 nephritis and a heterozygous rare variant, P453S, in CFHR5. The P453S variant, characterized by amino acid substitutions with a low allele frequency, was located in the region essential for CFHR5 protein function, and multiple in silico analyses were done suggesting the pathological significance of P453S. The renal function of our patient remains stable. The P453S variant might contribute to the suppression of the CFHR5 protein's function, resulting in gradual complement progression and a favorable renal prognosis.

To interpret and analyze the changing patterns of histology and direct immunofluorescence findings in membranoproliferative glomerulonephritis

Background

Membranoproliferative glomerulonephritis has in the recent past been regrouped into immune complex-mediated (ICM MPGN) disease (driven by the classical complement pathway) and complement-mediated (C3GN) disease (driven by the alternative complement pathway) based on pathogenetic role of alternative complement pathway and immunofluorescence deposits. The proposed regrouping lent therapeutic and prognostic support in managing the disease of MPGN.

Aims and Objectives

The present study is undertaken to study the patterns of MPGN based on histopathological and DIF examination and sub-categorize the cases into mainly complement dominant and immune complex-mediated diseases for better prognostic and therapeutic utility.

Materials and Methods

This is a prospective observational study carried out in a tertiary care center over a period of 2 yrs. The clinically suspected cases of MPGN were subjected to histopathologic and direct immunofluorescence examination (DIF), and the findings were interpreted in light of complement-mediated and immune complex-mediated MPGN.

Results

Out of 620 renal biopsies, diagnosis of MPGN was confirmed both on histopathology and DIF in 36 cases accounting for 5.8% of all biopsies. Based on DIF findings, the various groups comprised 20 cases (55.6%) of immune complex deposits, 11 (30.5%) of C3 dominant picture, and 5 (13.9%) of Nil immune deposits. On analysis of the patterns on DIF, 16 cases (80%) of C3 + Ig group and 6 (54.5%) of C3GN group showed predominantly MPGN pattern. Crescentic glomerulonephritis, global glomerulosclerosis, and interstitial fibrosis were markedly observed in C3GN group.

Conclusion

DIF is of immense prognostic and therapeutic value in managing cases of MPGN.

Efficacy and Safety of Iptacopan in Patients With C3 Glomerulopathy

Introduction

Complement 3 glomerulopathy (C3G) is a rare inflammatory kidney disease mediated by dysregulation of the alternative complement pathway. No targeted therapy exists for this aggressive glomerulonephritis. Efficacy, safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) (measured by complement biomarkers) of iptacopan were assessed in patients with C3G.

Methods

In this phase 2, multicenter, open-label, single-arm, nonrandomized study, adults with biopsy-proven, native kidney C3G (native cohort) and kidney transplant recipients with C3G recurrence (recurrent kidney transplant [KT] cohort) received iptacopan twice daily (bid) for 84 days (days 1-21: 10-100 mg; days 22-84: 200 mg). The primary end point was the urine protein-to-creatinine ratio (UPCR; native cohort) and the change in the C3 deposit score of kidney biopsy (recurrent KT cohort). The complement pathway measures included Wieslab assay, soluble C5b9, and serum C3 levels.

Results

A total of 27 patients (16 native cohort and 11 recurrent KT cohort) were enrolled and all completed the study. In the native cohort, UPCR levels decreased by 45% from baseline to week 12 (P = 0.0003). In the recurrent KT cohort, the median C3 deposit score decreased by 2.50 (scale: 0-12) on day 84 versus baseline (P = 0.03). Serum C3 levels were normalized in most patients; complement hyperactivity observed pretreatment was reduced. Severe adverse events (AEs) included post-biopsy hematuria and hyperkalemia. No deaths occurred during the study.

Conclusion

Iptacopan resulted in statistically significant and clinically important reductions in UPCR and normalization of serum C3 levels in the native cohort and reduced C3 deposit scores in the recurrent KT cohort with favorable safety and tolerability. (ClinicalTrials.gov identifier: NCT03832114).

Expert Discussion on Challenges in C3G Diagnosis: A Podcast Article on Best Practices in Kidney Biopsies

Complement 3 glomerulopathy (C3G) is an ultra-rare, progressive kidney disease resulting from dysregulation of the alternative complement pathway. Clinical presentation of C3G is heterogeneous and definitive diagnosis relies on kidney biopsy and immunofluorescence staining. The term C3G encompasses two subgroups, dense deposit disease and C3 glomerulonephritis, distinguished via electron microscopy. In this podcast article, the authors discuss the challenges associated with C3G diagnosis and the central role of kidney biopsy. Using an illustrative case study, key histological observations are described, and best practices are discussed from the perspectives of a nephrologist and a nephropathologist. Podcast Audio (MP4 141866 KB).

Rare Variants in Complement Gene in C3 Glomerulopathy and Immunoglobulin-Mediated Membranoproliferative GN

BACKGROUND

C3 glomerulopathy and idiopathic immunoglobulin-mediated membranoproliferative GN (Ig-MPGN) are rare complement-mediated kidney diseases. Inherited forms of C3 glomerulopathy/Ig-MPGN are rarely described.

METHODS

Three hundred ninety-eight patients with C3 glomerulopathy ( n =296) or Ig-MPGN ( n =102) from a national registry were screened for three complement genes: factor H ( CFH ), factor I ( CFI ), and C3 . Patients with rare variant (minor allele frequency <0.1%) were included. Epidemiologic, clinical, and immunologic data at diagnosis and kidney outcomes of patients were retrospectively collected.

RESULTS

Fifty-three different rare variants, including 30 (57%), 13 (24%), and ten (19%) in CFH , CFI , and C3 variants, were identified in 66/398 (17%) patients. Thirty-eight (72%) variants were classified as pathogenic, including 20/30 (66%) and 11/13 (84%) variants in CFH and CFI , respectively, impairing synthesis of factor H or factor I regulators. Fifteen of 53 (27%) variants were of unknown significance. At diagnosis, 69% of patients were adult (median age of 31 years). With the exception of biologic stigma of thrombotic microangiopathy, which was more frequent in patients with CFI variants (5/14 [36%] versus 1/37 [3%] and 0% in the CFH group and C3 group, respectively, P < 0.001), the clinical and histologic features were similar among the three variants groups. The kidney outcome was poor regardless of the age at onset and treatment received. Sixty-five percent (43/66) of patients with rare variant reach kidney failure after a median delay of 41 (19-104) months, compared with 28% (55/195) after a median delay of 34 (12-143) months in the nonvariant group. Among 36 patients who received a kidney transplant, 2-year recurrence was frequent, occurring in 39% (12/31), without difference between variant groups, and led to graft failure in three cases.

CONCLUSIONS

In our cohort, 17% of C3 glomerulopathy/Ig-MPGN cases were associated with rare variants in the CFH , CFI , or C3 genes. In most cases, a quantitative deficiency in factor H or factor I was identified. The presence of a rare variant was associated with poor kidney survival.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/CJASN/2023_11_08_CJN0000000000000252.mp3.

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.

C3 Glomerulopathy With Concurrent Thrombotic Microangiopathy: Clinical and Immunological Features

RATIONALE & OBJECTIVE

C3 glomerulopathy (C3GN) and atypical hemolytic uremic syndrome (aHUS) are 2 distinct rare kidney diseases caused by dysregulation of the alternative complement pathway. Patients with C3GN and concurrent kidney lesions of thrombotic microangiopathy (TMA) have been rarely reported. We characterized the clinical features and underlying immunological abnormalities in these patients.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

Patients with C3GN and concomitant TMA lesions on biopsy registered from 2009 to 2019 in the French National Registry of C3GN.

FINDINGS

Among 278 registered patients with C3GN, 16 (6%) had biopsy-proven glomerular and/or vascular TMA lesions. Their median age at diagnosis was 39 years (range, 7-76), and 59% were female. Fourteen of the 16 patients (88%) had an estimated glomerular filtration rate of<30mL/min/1.73m2 and 3 of 16 (19%) required dialysis. Twelve of the 14 evaluated patients (86%) showed evidence of mechanical hemolysis. Fifty percent of the patients had low C3 levels. Six of the 14 evaluated patients had a rare variant in complement genes, and 4 of the 16 patients (25%) had monoclonal gammopathy. Among the 16 patients, 10 (63%) received eculizumab, 5 (31%) received immunosuppressive therapy, and 4 (25%) received clone-targeted chemotherapy. Median kidney survival was 49 months.

LIMITATIONS

Small retrospective case series with a limited number of biopsies including electron microscopy.

CONCLUSIONS

Concomitant C3GN and TMA is extremely rare and is associated with poor kidney outcomes. Genetic or acquired abnormalities of the alternative complement pathway are common as is the presence of monoclonal gammopathy, which may inform the selection of treatment approaches.

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.

Pathogenesis of autoimmune disease

Autoimmune diseases are a diverse group of conditions characterized by aberrant B cell and T cell reactivity to normal constituents of the host. These diseases occur widely and affect individuals of all ages, especially women. Among these diseases, the most prominent immunological manifestation is the production of autoantibodies, which provide valuable biomarkers for diagnosis, classification and disease activity. Although T cells have a key role in pathogenesis, they are technically more difficult to assay. In general, autoimmune disease results from an interplay between a genetic predisposition and environmental factors. Genetic predisposition to autoimmunity is complex and can involve multiple genes that regulate the function of immune cell populations. Less frequently, autoimmunity can result from single-gene mutations that affect key regulatory pathways. Infection seems to be a common trigger for autoimmune disease, although the microbiota can also influence pathogenesis. As shown in seminal studies, patients may express autoantibodies many years before the appearance of clinical or laboratory signs of disease - a period called pre-clinical autoimmunity. Monitoring autoantibody expression in at-risk populations may therefore enable early detection and the initiation of therapy to prevent or attenuate tissue damage. Autoimmunity may not be static, however, and remission can be achieved by some patients treated with current agents.

Clinico-Pathogenic Similarities and Differences between Infection-Related Glomerulonephritis and C3 Glomerulopathy

Recently, the comprehensive concept of "infection-related glomerulonephritis (IRGN)" has replaced that of postinfectious glomerulonephritis (PIGN) because of the diverse infection patterns, epidemiology, clinical features, and pathogenesis. In addition to evidence of infection, hypocomplementemia particularly depresses serum complement 3 (C3), with endocapillary proliferative and exudative GN developing into membranoproliferative glomerulonephritis (MPGN); also, C3-dominant or co-dominant glomerular immunofluorescence staining is central for diagnosing IRGN. Moreover, nephritis-associated plasmin receptor (NAPlr), originally isolated from the cytoplasmic fraction of group A Streptococci, is vital as an essential inducer of C3-dominant glomerular injury and is a key diagnostic biomarker for IRGN. Meanwhile, "C3 glomerulopathy (C3G)", also showing a histological pattern of MPGN due to acquired or genetic dysregulation of the complement alternative pathway (AP), mimics C3-dominant IRGN. Initially, C3G was characterized by intensive "isolated C3" deposition on glomeruli. However, updated definitions allow for glomerular deposition of other complement factors or immunoglobulins if C3 positivity is dominant and at least two orders of magnitude greater than any other immunoreactant, which makes it challenging to quickly distinguish pathomorphological findings between IRGN and C3G. As for NAPlr, it was demonstrated to induce complement AP activation directly in vitro, and it aggravates glomerular injury in the development of IRGN. A recent report identified anti-factor B autoantibodies as a contributing factor for complement AP activation in pediatric patients with PIGN. Moreover, C3G with glomerular NAPlr deposition without evidence of infection was reported. Taken together, the clinico-pathogenic features of IRGN overlap considerably with those of C3G. In this review, similarities and differences between the two diseases are highlighted.

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.

Use of Histologic Parameters to Predict Glomerular Disease Progression: Findings From the China Kidney Biopsy Cohort Study

RATIONALE & OBJECTIVE

Challenges in achieving valid risk prediction and stratification impede treatment decisions and clinical research design for patients with glomerular diseases. This study evaluated whether chronic histologic changes, when complementing other clinical data, improved the prediction of disease outcomes across a diverse group of glomerular diseases.

STUDY DESIGN

Multicenter retrospective cohort study.

SETTING & PARTICIPANTS

4,982 patients with biopsy-proven glomerular disease who underwent native biopsy at 8 tertiary care hospitals across China in 2004-2020.

NEW PREDICTORS & ESTABLISHED PREDICTORS

Chronicity scores depicted as 4 categories of histological chronic change, as well as baseline clinical and demographic variables.

OUTCOME

Progression of glomerular disease defined as a composite of kidney failure or a ≥40% decrease in estimated glomerular filtration rate from the measurement at the time of biopsy.

ANALYTICAL APPROACH

Multivariable Cox proportional hazard models. The performance of predictive models was evaluated by C statistic, time-dependent area under the receiver operating characteristic curve (AUROC), net reclassification index, integrated discrimination index, and calibration plots.

RESULTS

The derivation and validation cohorts included 3,488 and 1,494 patients, respectively. During a median of 31 months of follow-up, a total of 444 (8.9%) patients had disease progression in the 2 cohorts. For prediction of the 2-year risk of disease progression, the AUROC of the model combining chronicity score and the Kidney Failure Risk Equation (KFRE) in the validation cohort was 0.76 (95% CI, 0.65-0.87); in comparison with the KFRE model (AUROC, 0.68 [95% CI, 0.56-0.79]), the combined model was significantly better (P = 0.04). The combined model also had a better fit, with a lower Akaike information criterion and a significant improvement in reclassification as assessed by the integrated discrimination improvements and net reclassification improvements. Similar improvements in predictive performance were observed in subgroup and sensitivity analyses.

LIMITATIONS

Selection bias, relatively short follow-up, lack of external validation.

CONCLUSIONS

Adding histologic chronicity scores to the KFRE model improved the prediction of kidney disease progression at the time of kidney biopsy in patients with glomerular diseases.

PLAIN-LANGUAGE SUMMARY

Risk prediction and stratification remain big challenges for treatment decisions and clinical research design for patients with glomerular diseases. The extent of chronic changes is an important component of kidney biopsy evaluations in glomerular disease. In this large multicenter cohort including 4,982 Chinese adults undergoing native kidney biopsy, we evaluated whether histologic chronicity scores, when added to clinical data, could improve the prediction of disease prognosis for a diverse set of glomerular diseases. We observed that adding histologic chronicity scores to the kidney failure risk equation improved the prediction of kidney disease progression at the time of kidney biopsy in patients with glomerular diseases.

Overlap of C3 Glomerulopathy and Thrombotic Microangiopathy: A Case Series

Introduction

Dysregulation of alternative complement pathway underlies the pathogenesis of both C3 glomerulopathy (C3G) and thrombotic microangiopathy (TMA). In this study, we describe both disease entities occurring in 5 patients.

Methods

We identified 114 patients at our institution from 2007 to 2016 with C3G in native kidney biopsies and those with concurrent TMA were included.

Results

The median age at diagnosis was 58 years (range: 28-69); all were male. Median serum creatinine and proteinuria at presentation were 2.3 mg/dl and 2089 mg/d, respectively. Three cases presented with TMA-predominant phenotype and 2 with C3G-predominant phenotype. Immunofluorescence (IF) showed bright C3 staining in mesangium and/or capillary walls. Electron microscopy showed marked subendothelial expansion by fluffy material in the capillary loops without associated deposits. However, capillary wall deposits were present in other loops in 4 cases. Mesangial deposits were present in all cases. Four cases showed low C3, of which 2 showed low C4. Complement evaluation in 3 cases showed pathogenic CFH mutation in 1 case, and multiple variant of unknown significance along with factor B autoantibody and C4 nephritic factor in 1 case. One patient negative for complement abnormalities had a monoclonal gammopathy. Three cases were treated with steroids and/or immunosuppressants. One case progressed to end-stage renal disease (ESRD) at 38.3 months; the remaining showed median serum creatinine and proteinuria of 2.5 mg/dl and 1169 mg/d, respectively at median follow-up of 17.5 months.

Conclusion

Overlap of C3G and TMA is rare and can clinically present as C3G-predominant or TMA-predominant phenotype. The significance of concurrent C3G/TMA findings on long-term renal survival remains to be explored.