A multi-institutional study found a possible role of anti-nephrin antibodies in post-transplant focal segmental glomerulosclerosis recurrence

Advances in the pathophysiology and treatment of focal segmental glomerulosclerosis: The importance of a timely and tailored approach

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of glomerular damage that significantly contributes to chronic kidney disease and end-stage renal disease. Its incidence is rising globally, necessitating timely and personalized management strategies. This paper aims to provide an updated overview of the pathophysiology, diagnosis, and therapeutic strategies for FSGS, emphasizing the importance of early interventions and tailored treatments. This editorial synthesizes key findings from recent literature to highlight advancements in understanding and managing FSGS. Emerging evidence supports the role of targeted therapies and personalized approaches in improving outcomes for FSGS patients. Advances include novel biomarkers, genetic testing, and innovative therapeutics such as transient receptor potential ion channel blockers and antisense oligonucleotides for apolipoprotein 1-related FSGS. Effective management of FSGS requires a combination of timely diagnosis, evidence-based therapeutic strategies, and ongoing research to optimize patient outcomes and address gaps in the current understanding of the disease.

Evaluation of Methodologies in Anti-nephrin Autoantibody Detection

INTRODUCTION

Recent studies discovered the prominent presence of anti-nephrin autoantibodies in minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS). However, widely different, and often unconventional autoantibody detection methods were used in these studies, making it challenging to standardize anti-nephrin antibody detection and quantification across different studies.

METHODS

Here, we compare methods of conventional ELISA, immunoprecipitation (IP)- based on-beads ELISA, immunoprecipitation-Western blotting (IP-WB), and cell- and tissue-based immunofluorescence staining with two cohorts totaling 169 patients and control individuals.

RESULTS

Different assay methods and antigen preparations led to method-specific false-positive and false-negative results. In general, high-quality antigens produced in human cells, combined with IP-based assays, yielded the most robust and reliable results. Among 63 and 24 samples from patients with FSGS or MCD, respectively, two patients with FSGS showed strong antibody signals in both ELISA-based assays and IP-WB, while approximately half of patients with MCD had weak signals detectable only by IP-WB.

CONCLUSION

These findings highlight the importance of standardizing antibody detection methods.

Anti-nephrin antibodies guide living donor kidney transplantation in a pediatric patient with primary focal segmental glomerular sclerosis

INTRODUCTION

Disease recurrence after kidney transplantation (KTx) remains a major challenge in patients with primary focal segmental glomerulosclerosis (pFSGS). Antibodies targeting the slit diaphragm protein nephrin have been identified in patients with early disease recurrence. Here, we describe monitoring and effective pre-transplant elimination of anti-nephrin antibodies in an adolescent with pFSGS prior to living-donor KTx.

METHODS

Anti-nephrin antibodies were assessed in pre- and post-transplant serum samples by ELISA, Western blot and immunoprecipitation using three different nephrin proteins.

RESULTS

Pre-transplant treatment including rituximab and repetitive therapeutic plasma exchanges resulted in effective and sustainable reduction of anti-nephrin antibodies. Allograft function has remained excellent without albuminuria over a follow-up of more than one year. Further analysis showed, that the antibodies were cross-reactive with NEPH3 (filtrin), another key slit diaphragm protein.

CONCLUSIONS

Monitoring and pre-transplant elimination of anti-slit diaphragm antibodies may become a standard, personalized approach in patients with pFSGS requiring KTx.

Kidney organoids: a 3-dimensional tool to unmask permeability factors in primary and recurrent FSGS

Primary focal segmental glomerulosclerosis is a glomerular disorder associated with a high risk of recurrence after transplantation. Compelling evidence supports the existence of circulating permeability factors whose identity remains elusive. In the current issue of Kidney International, Gupta et al. propose that kidney organoid can respond to these factors in patients with focal segmental glomerulosclerosis and may serve as a potential platform for predicting disease recurrence. Future studies are required to identify the critical factors driving focal segmental glomerulosclerosis recurrence and to develop a standardized organoid platform for predicting clinical outcome.

Genetic aspects of pediatric nephrotic syndrome and anti-nephrin antibodies

Nephrotic syndrome is the most common glomerular disease in children, and various hypotheses regarding its etiology have been proposed, primarily focusing on immune-related mechanisms. Nephrotic syndrome can manifest as a monogenic disease caused by deleterious variants in genes such as NPHS1, which encodes nephrin. In steroid-sensitive nephrotic syndrome, HLA class II and immune-related genes have been identified as susceptibility genes. Moreover, NPHS1 is a susceptibility gene for steroid-sensitive nephrotic syndrome in patients from East Asian populations. Anti-nephrin antibodies have been identified as a significant factor in the pathogenesis of nephrotic syndrome. These discoveries have substantially advanced our understanding of nephrotic syndrome. However, the mechanisms underlying the production of anti-nephrin antibodies and their association with genetic backgrounds have remained unclear and warrant further investigation.

A kidney organoid-based readout to assess disease activity in primary and recurrent focal segmental glomerulosclerosis

Primary focal segmental glomerulosclerosis (pFSGS) is an acquired kidney disorder that frequently leads to kidney failure and confers an elevated risk of recurrence after kidney transplantation, termed recurrent pFSGS. Unfortunately, there is no diagnostic method to foresee recurrence of pFSGS after kidney transplantation. Progress in developing assays to test disease activity is hampered by few preclinical models to replicate disease and inability of in vitro cultured primary podocytes to remain terminally differentiated. In recent years, advancements in kidney organoid biology have led to the development of kidney tissues with glomeruli and major nephron segments including podocytes. To develop a pFSGS model, we studied the effect of plasma from patients diagnosed with pFSGS on kidney organoids differentiated from human pluripotent stem cells. The pFSGS plasma treatment induced podocytopathy, extracellular matrix protein deposition, fibrosis and apoptosis within organoids, whereas non-recurrent plasma did not affect organoid structure. pFSGS plasma also led to loss of normal expression patterns of podocyte specific proteins, nephrin and podocin within podocytes. Further, cytokine array profiling revealed that pFSGS plasma induced secretion of cytokines associated with inflammation and angiogenesis. Additionally, kidney organoids treated with plasma obtained after therapeutic plasma exchange for recurrent pFSGS led to lower cell death in organoids after sequential exchanges with the final exchange showing the least apoptotic cells without morphological abnormality. Overall, our results demonstrate the potential of kidney organoids in advancing kidney disease modeling. These insights could be applied in clinical settings to assist in gauging FSGS recurrence risk prior to kidney transplantation.

Potential and pitfalls of measuring circulating anti-nephrin autoantibodies in glomerular diseases

Recent studies have identified autoantibodies targeting the podocyte protein nephrin in patients with primary podocytopathies such as minimal change disease, primary focal segmental glomerulosclerosis (FSGS), post-transplant recurrent FSGS and childhood idiopathic nephrotic syndrome. These antibodies bind nephrin and directly influence nephrin downstream signaling, with immense effect on the podocytes' cellular structure and function, substantially changing our understanding of antibody-mediated podocytopathies and disease classification. Their presence correlates with disease activity and holds great potential as a novel biomarker of anti-nephrin-associated podocytopathy. However, the detection of these potentially low-titre autoantibodies has proven challenging. In this review, we highlight and explain distinct detection methodologies with their advantages and disadvantages and discuss the potential of anti-nephrin autoantibodies as a novel biomarker in nephrotic syndrome for diagnosis, prognostication and therapeutic guidance in patients with nephrotic syndrome.

Primary FSGS is not associated with worse kidney outcome compared with other FSGS subtypes

Background

Studies that compare kidney outcomes across patients with different forms of focal segmental glomerulosclerosis (FSGS) are lacking.

Methods

This retrospective study compared annual estimated glomerular filtration rate (eGFR) slope and kidney failure rate (eGFR <15 mL/min/1.73 m2 or initiation of kidney replacement therapy) across patients with biopsy-proven primary, maladaptive, genetic and undetermined FSGS. Patients were included from two Belgian tertiary referral hospitals, from 2010 until 2022. Associations between covariates and kidney failure were estimated using Cox and Fine and Gray models. eGFR slopes were estimated using linear mixed-effects models.

Results

Eighty-two patients were subdivided into primary (28.1%), maladaptive (40.2%), genetic (14.6%) and undetermined FSGS (17.1%) groups. Kidney failure occurred in 22 patients (26.8%). Primary FSGS patients exhibited higher baseline eGFR and less chronic changes on biopsy. The annual eGFR slope was -2.5 mL/min in primary, -2.5 mL/min in maladaptive, -4.6 mL/min in genetic and -4.4 mL/min in undetermined FSGS. Female sex was associated with a lower kidney failure rate and higher eGFR slope. Higher proteinuria at biopsy was associated with a higher kidney failure rate, lower eGFR slope and a higher mortality rate. Global sclerosis on kidney biopsy was associated with lower baseline eGFR, while a higher percentage of segmental sclerosis rather associated with more rapid eGFR decline [-1.5 mL/min/year per 10% increase, 95% confidence interval (-2.2, -0.7)].

Conclusions

Patients with primary FSGS were biopsied earlier in their disease course and exhibited surprisingly good kidney outcome. Overall, sex, baseline eGFR, proteinuria and the degree of focal and global glomerulosclerosis play a more important role in estimating the prognosis of patients with FSGS than merely the FSGS etiology.

Low Density Lipoprotein Apheresis for Treatment of Focal Segmental Glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) has become one the leading causes of kidney disease in the United States. With the incidence of FSGS rising over the past decade, capable treatment options have been a large focus in research. One therapy that shows promise is low density lipoprotein apheresis (LDL-A). This procedure removes lipoproteins containing apolipoprotein-B from the blood, thus reducing the lipid load on the renal system. LDL-A also improves responsiveness to the standard FSGS therapy of corticosteroids and cyclosporine. This paper describes the current LDL-A techniques, offers insight to existing clinical studies employing this therapy, and ultimately highlights LDL-A as a treatment option for FSGS, post-renal transplant, and nephrotic syndrome.

Anti-nephrin antibodies in adult Chinese patients with minimal change disease and primary focal segmental glomerulosclerosis

Anti-nephrin autoantibodies have been discovered in patients with minimal change disease (MCD) and primary focal segmental glomerulosclerosis (FSGS), especially in those with active nephrotic syndrome. Here, we investigated the prevalence and clinical significance of anti-nephrin antibodies in 596 adult Chinese patients (436 with MCD and 160 with primary FSGS) diagnosed by kidney biopsy. Anti-nephrin IgG and IgM were detected using ELISA, with validation through antigen-inhibition ELISA and Western blotting. Clinical data at biopsy and during the follow-up period were analyzed. Anti-nephrin antibodies were detected in 43% of all patients, with 30% testing positive for anti-nephrin IgG, 26% for anti-nephrin IgM, and 13.1% for both antibodies. The prevalence of anti-nephrin antibodies was higher in patients with nephrotic-range proteinuria who were not receiving steroids or immunosuppressants (51.1%). Patients with positive anti-nephrin antibodies exhibited more severe nephrotic syndrome, higher rates of relapse, and a shorter relapse-free period compared to those negative for these antibodies. Clinical features were similar between those with IgG and IgM. Notably, patients with both anti-nephrin IgG and IgM had the most severe proteinuria and the highest relapse frequency, suggesting a dose-dependent effect. Longitudinal analysis revealed that anti-nephrin antibodies significantly decreased during clinical remission, while they reappeared preceding proteinuria relapse. Our study shows that anti-nephrin antibodies, including IgG and IgM, are detectable in adult patients with MCD and primary FSGS and are associated with active nephrotic syndrome and frequent relapse. These antibodies may serve as valuable biomarkers and potential therapeutic targets.

Hydrogeochemical forecasting in a tribal stretch infected with chronic kidney disease of unknown etiology

A tribal stretch in central India has been silently suffering from the enigmatic chronic kidney disease of unknown etiology (CKDu) for the past many years. It drew national attention in 2018 when over a quarter of the population from a single village of 1200 people got hospitalized with at least 100 deaths in a few years' span. This contribution tries to understand the geochemical genesis of the problem and its evolution process through a study of major rock-water interactions. The future hydrogeochemical environment of the area has been forecasted based on saturation indices of several key minerals. Finally, a probabilistic estimation of the population's exposure to the Hofmeister ion series has been made to understand the role of the specific ion effect on the onset of CKDu. Three distinct chemical facies have been identified based on the analytical results of 27 groundwater samples: Ca2+-Mg2+-HCO3- (55.56 %), Ca2+-Mg2+-Cl--SO42- (29.63 %), and Na+-K+-HCO3- (14.81 %). The positive loadings (r) of EC and TDS with Ca2+ (0.89; 0.98), Mg2+ (0.79; 0.89), Na+ (0.78; 0.48), Cl- (0.99; 0.93), and NO3- (0.72; 0.85) have led to groundwater hardness and salinity. Ion exchange processes and saturation indices of the geogenic minerals, such as anhydrite, gypsum, fluorite, halite, and sylvite, play crucial roles in the mineralization process. As these minerals progress toward full saturation, their dissolution with the host aquifers releases more of Ca2+, Na+, K+, SO42-, Cl- and F- ions continually. This exacerbates the fluorosis problem besides increasing salinity and water hardness in the study area. The combined effects of Ca2++Mg2+ ions with a control on the total hardness, increased Na+/Ca2+ ratio, and excess F- ions in groundwater are suspected to be the inducing factors for CKDu. This hypothesis is strongly supported by the occurrence of Hofmeister phenomena in the tubular areas of human kidneys through ingested groundwater.

Is There a Diagnostic and Prognostic Role for Anti-Nephrin Autoantibodies in Diabetic Nephropathy?

Diabetic nephropathy (DN) is one of the key causes of end-stage kidney disease worldwide, especially in developed countries. The classic pathogenic development of DN is characterized by microalbuminuria which would progress to nephrotic-range proteinuria and loss of kidney function. The degree of albuminuria is considered an independent risk factor for all-cause mortality in patients with DN. It is now well established that albuminuria stems from disruptions in podocyte structure and function. Podocytes play a major role in the glomerular filtration barrier. The nephrin protein has been identified as a core component of the slit diaphragm in podocytes, and as such, the downregulation of nephrin expression has been described well in various proteinuric glomerulopathies, including DN. Previous studies have shown that the presence of urinary nephrin potentially signifies an early marker of podocyte injury in DN. More recently, there have been increasing bodies of evidence which suggest that circulating autoantibodies targeting nephrin contributes to the pathogenesis of podocytopathies. However, the functional significance of these circulating autoantibodies in patients with DN is not well understood. In this review, we aim to evaluate the significance of nephrin dysregulation in the pathogenesis of DN based on the current available literature and provide an overview on the application of circulating anti-nephrin autoantibodies in relation to its diagnostic as well as prognostic role in podocytopathies, including DN.

Autoantibodies Targeting Proteasome Subunit Alpha Type 1 in Autoimmune Podocytopathies

Key Points

Serum anti-proteasome subunit alpha type 1 (PSMA1) autoantibodies were specifically elevated in the active phase of idiopathic nephrotic syndrome, which may assist in disease diagnosis and monitoring. Serum anti-PSMA1 antibodies could cause damage to the glomerular filtration barrier, which may be a pathogenic antibody of idiopathic nephrotic syndrome. PSMA1 played an important role in the maintenance of podocyte morphology and function.

Background

The antibody against proteasome subunit alpha type 1 (PSMA1) is a podocyte autoantibody in children with idiopathic nephrotic syndrome identified in our previous study. The aim of this study was to explore the characteristics of idiopathic nephrotic syndrome in children and the mechanism underlying its involvement in the development of idiopathic nephrotic syndrome.

Methods

The levels of serum anti-PSMA1 autoantibodies in children were detected through protein microarray and compared among different disease groups. The recombinant PSMA1 protein was injected subcutaneously and intraperitoneally into mice to observe glomerular morphology and function. The PSMA1-knockdown and PSMA1-overexpressing cell lines were constructed from mouse podocytes, and their cytoskeleton and function were analyzed. Homozygous zebrafish with psma1 knockout were observed.

Results

The levels of serum anti-PSMA1 autoantibodies were higher in children with idiopathic nephrotic syndrome and varied with urinary protein. In mice immunized with PSMA1, the presence of serum anti-PSMA1 autoantibody caused albuminuria and damage to the glomerular filtration membrane. Deficiency of PSMA1 impaired the podocyte cytoskeleton and physiological function. Complete deletion of psma1 caused edema, abnormal glomerular morphology, and effacement of foot processes in zebrafish.

Conclusions

PSMA1 played an important role in the maintenance of podocyte morphology and function.

Impact of Therapeutic Plasma Exchange and Rituximab for Prevention of Idiopathic Focal Segmental Glomerulosclerosis Recurrence Post-Kidney Transplantation

Background

Focal segmental glomerulosclerosis (FSGS) recurs after kidney transplantation (KT) in 30%-50% of recipients. Recurrence is associated with early graft loss in up to 60% of cases. This study aimed to assess the efficacy of therapeutic plasma exchange (TPE) combined with rituximab (RTX) in preventing early FSGS recurrence within 1 y post-KT.

Methods

This single-center, retrospective cohort study included patients receiving KT for idiopathic FSGS between June 2013 and August 2021. In May 2016, a preventative FSGS protocol was implemented where KT recipients with idiopathic FSGS received perioperative sessions of TPE followed by a dose of RTX with or without IVIG. The incidence of recurrent FSGS within the first year posttransplantation was assessed between the FSGS protocol cohort versus the historical group of patients who did not undergo prophylactic treatment.

Results

A total of 65 patients received KT for idiopathic FSGS during the study period. Forty patients were included in the FSGS protocol cohort and 25 in the control cohort. When assessing clinical recurrence with proteinuria, there were significantly fewer cases in the FSGS protocol cohort versus the control cohort, 1 versus 5 patients (3% versus 20%, P = 0.03). There were no instances of death-censored graft loss at 1 y in the protocol cohort versus 2 cases in the control cohort (0% versus 8%, P = 0.14).

Conclusions

TPE combined with RTX may prevent early FSGS recurrence without significant rates of infection.

When should the nephrologist think about genetics in patients with glomerular diseases?

This review discusses the significance of genetics in diagnosing glomerular diseases. Advances in genetic testing, particularly next-generation sequencing, have improved the accessibility and accuracy of diagnosing monogenic diseases, allowing for targeted gene panels and whole-exome/genome sequencing to identify genetic variants associated with glomerular diseases. Key indicators for considering a genetic cause include the age of onset, extrarenal features, family history, and inconclusive kidney biopsy results. Early-onset diseases, for instance, have a higher likelihood of being genetically caused, while extrarenal manifestations can also suggest an underlying genetic condition. A thorough family history can reveal patterns of inheritance that point to monogenic causes, although complexities like incomplete penetrance, skewed X inactivation and mosaicism can complicate the assessment. Also, autosomal recessive conditions imply asymptomatic parents, making genetic suspicion less likely, while de novo mutations can occur without any family history, further obscuring genetic assessment. Focal segmental glomerulosclerosis (FSGS) is characterized by podocyte injury and depletion, presenting in various forms, including primary, genetic, and secondary FSGS. Accurate classification of FSGS patients based on clinical and histological features is essential for guiding treatment decisions, optimizing therapeutic plans, avoiding unnecessary immunosuppression, and predicting relapse risk after kidney transplantation. Overall, a clinicopathological approach, enriched by genetic testing, offers a precise framework for diagnosis and management in glomerular diseases. Future directions for research and clinical practice include potential advancements in genetic testing and personalized medicine, which could further improve diagnostic precision and individualized treatment strategies.

Prophylactic treatment of FSGS recurrence in patients who relapsed on a previous kidney graft

BACKGROUND

Recurrence of focal segmental glomerulosclerosis (FSGS) is common after kidney transplantation and is classically associated with a significant decrease in graft survival. A major risk factor is a prior history of FSGS recurrence on a previous graft. This analysis reports the impact of a prophylactic treatment of FSGS recurrence in very high-risk patients who experienced a recurrence on a previous graft.

METHODS

We performed a retrospective multicentre observational study in 25 French transplantation centres. The inclusion criteria were patients aged more than 18 years who had undergone kidney transplant between 31 December 2004 and 31 December 2020, and who had a history of FSGS recurrence on a previous graft.

RESULTS

We identified 66 patients: 40 received prophylactic treatment (PT+), including intravenous cyclosporine and/or rituximab and/or plasmapheresis, and 26 did not receive any prophylactic treatment (PT-). The time to progression to end-stage kidney disease was similar between groups. The PT+ group was younger at FSGS diagnosis and at the time of kidney retransplantation and lost their previous graft faster. The overall recurrence rate was 72.7% (76.9% in the PT- group and 70.0% in the PT+ group, P = .54). At least partial remission was achieved in 87.5% of patients. The 5-year graft survival was 67.7% [95% confidence interval (CI) 53.4%-78.4%]: 65.1% (95% CI 48.7%-77.4%) in patients with FSGS recurrence vs 77.3% (95% CI 43.8%-92.3%) in patients without recurrence (P = .48).

CONCLUSION

Our study suggests that prophylactic treatment should not be used routinely in patients receiving a second transplantation after recurrence of FSGS on a previous graft. The recurrence rate is high regardless of the use of prophylactic treatment. However, the 5-year graft survival remains satisfactory.

Advances in Focal Segmental Glomerulosclerosis Treatment From the Perspective of the Newest Mechanisms of Podocyte Injury

Podocyte injury was widely recognized as a fundamental mechanism driving the progression of focal segmental glomerulosclerosis (FSGS). Recent research has therefore focused on the development of targeted therapies aimed at disrupting specific pathogenic signaling cascades within podocytes, resulting in noteworthy advancements. The role of mechanisms such as alterations in the actin cytoskeleton, oxidative stress, mitochondrial dysfunction, and inadequate autophagy within the microenvironment of podocyte injury have garnered increasing attention. Corresponding targeted medications such as Abatacept, chemokine receptor (CCR) inhibitors, CDDO-Im (2-Cyano-3,12-dioxooleana-1,9-dien-28-imidazolide), adenosine monophosphate-activated protein kinase (AMPK) activators, and Adalimumab are currently under investigation. Notably, some medications such as Rituximab and Sparsentan, may simultaneously target multiple downstream mechanisms, Furthermore, exploring molecular strategies for established medications and developing novel treatments guided by biomarkers such as Anti-CD40 antibody, blood microRNA, urinary microRNA, and tumor necrosis factor-alpha (TNF-α) may provide additional therapeutic avenues for patients with FSGS.

The autoimmune architecture of childhood idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome, the most common glomerular disorder in children, has long been considered an immune-mediated disease based on the efficacy of glucocorticoids at inducing remission. Nevertheless, the immune processes leading to podocytopathy have largely remained elusive. The success of B-cell depletion with rituximab, descriptions of B-cell dysregulation during active disease, and the most recent discovery of autoantibodies targeting the major podocyte antigen nephrin point to an autoimmune humoral etiology for idiopathic nephrotic syndrome. Investigations of the immune factors involved in idiopathic nephrotic syndrome pathogenesis have uncovered common features with other autoimmune disorders that will aid in prognostication and in guiding the expansion of our glucocorticoid-sparing therapeutic arsenal. In this review, we discuss the emerging autoimmune architecture of idiopathic nephrotic syndrome, with a specific focus on pediatric steroid-sensitive disease, including the podocyte-reactive B-cell response that causes anti-podocyte antibodies, the predisposing genetic factors that shape the podocyte-reactive immune landscape, and the immune triggers driving active disease.

To biopsy or not to biopsy a teenager with idiopathic nephrotic syndrome? Biopsy first

Kidney biopsy plays a crucial role in the diagnosis and management of several glomerular diseases. While it is generally considered a routine and safe procedure in children, it should be conducted with the primary objective of addressing the following question: do the prognosis and treatments vary based on the findings of kidney biopsy? In children presenting with idiopathic nephrotic syndrome (INS), guidelines suggest to consider kidney biopsy for individuals older than 12 years, primarily due to the possible increased incidence of different glomerulonephritis compared to younger patients, who predominantly manifest with minimal change disease. However, these guidelines also advocate for uniform therapeutic strategies, typically steroids, irrespective of the age or histological findings. Whether the age of more than 12 years may be a recommendation for performing kidney biopsy at presentation of INS is debatable. Instead, kidney biopsy could be reserved for steroid-resistant cases. On the other hand, when kidney biopsy is performed in INS, particularly in focal segmental glomerulosclerosis, histology may reveal additional lesions, that are strongly associated with a poorer response to treatment and worse clinical outcomes. Therefore, current guidelines on treatments of nephrotic syndrome may appear overly restrictive, despite the relevant findings provided by kidney biopsy. Therefore, in the present manuscript, which is part of a pro-con debate on the management of nephrotic syndrome in adolescents, we emphasize the potential role of performing a kidney biopsy before initiating corticosteroid treatment.

Evaluation for genetic disease in kidney transplant candidates: A practice resource

The increasing availability of clinically approved genetic tests for kidney disease has spurred the growth in the use of these tests in kidney transplant practice. Neither the testing options nor the patient population where this should be deployed has been defined, and its value in kidney transplant evaluation has not been demonstrated. Transplant providers may not always be aware of the limitations of genetic testing and may need guidance on comprehending test results and providing counsel, as many centers do not have easy access to a renal genetic counselor or a clinical geneticist. In this practice resource, a working group of nephrologists, geneticists, and a genetic counselor provide a pragmatic, tailored approach to genetic testing, advocating for its use only where the genetic diagnosis or its exclusion can impact the choices available for transplantation or posttransplant management or the workup of living donor candidates at increased risk for heritable disease.

Indications for genetic testing in adults with focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of injury that derives from various pathological processes that affect podocytes, resulting in loss of selectivity of the glomerular filtration membrane, proteinuria and the development of renal failure that progresses to end-stage kidney disease in a significant number of patients. The classification proposed by the 2021 KDIGO guidelines divides FSGS into four categories: primary, secondary, genetic, and FSGS of undetermined cause, thus facilitating its diagnosis and management. Genetic causes of FSGS present significant clinical variability, complicating their identification. Genetic testing is crucial to identify FSGS of genetic cause. The prevalence of genetic FSGS is significant in children and considerable in adults, highlighting the importance of early diagnosis to avoid unnecessary treatments and facilitate genetic counselling. Massive sequencing techniques have revolutionized genetic diagnosis, allowing the identification of more than 60 genes responsible for podocyte damage. This document proposes clinical recommendations for carrying out genetic studies in adults with FSGS, highlighting the need for a correct classification for adequate therapeutic planning and improvement of results in clinical trials.

Past and future in vitro and in vivo approaches toward circulating factors and biomarkers in idiopathic nephrotic syndrome

Predicting the risks of progression to chronic kidney disease (CKD) stage 5 in idiopathic nephrotic syndrome (NS) and recurrence of the disease (rNS) following kidney transplantation (KT) is a key assessment to provide essential management information. NS has been categorized etiologically as genetic and immune-based. A genetic cause can be identified in ~ 30% of children with steroid-resistant NS (SRNS), a finding associated with a very low risk of rNS following KT. In immune-based NS, clinical overlap is observed among steroid-sensitive NS, secondary-resistant NS, and SRNS not associated with disease-causing genetic variants (non-monogenic SRNS). While ~ 50% of SRNS patients with no identified monogenic disease respond to intensified immunosuppressive treatments, the ones that do not respond to this therapy have a high risk of progression to CKD stage 5 and post-KT rNS. Secondary-resistant patients who progress to CKD stage 5 display the highest risk of post-KT rNS. The proposed shared underlying mechanism of the immune-based NS associated with post-KT rNS is based on a systemic circulating factor (CF) that affects glomerular permeability by inducing foot process effacement and focal segmental glomerulosclerosis. However, identifying patients without a detected genetic form who will recur post-KT is a major challenge. Extensive efforts, therefore, have been made to identify CFs and biomarkers potentially capable of predicting the risk of progression to CKD stage 5 and post-KT rNS. This review discusses the in vitro and in vivo approaches employed to date to identify and characterize potential CFs and CF-induced biomarkers of recurrent NS and offers an assessment of their potential to improve outcomes of KT in this patient population.

Pathogenesis of Focal Segmental Glomerulosclerosis and Related Disorders

Focal segmental glomerulosclerosis (FSGS) is the morphologic manifestation of a spectrum of kidney diseases that primarily impact podocytes, cells that create the filtration barrier of the glomerulus. As its name implies, only parts of the kidney and glomeruli are affected, and only a portion of the affected glomerulus may be sclerosed. Although the diagnosis is based primarily on microscopic features, patient stratification relies on clinical data such as proteinuria and etiological criteria. FSGS affects both children and adults and has an elevated risk of progression to end-stage renal disease. The prevalence of FSGS is rising among various populations, and the efficacy of various therapies is limited. Therefore, understanding the pathophysiology of FSGS and developing targeted therapies to address the complex needs of FSGS patients are topics of great interest that are currently being studied across various clinical trials. We discuss the etiology of FSGS, describe the major contributing pathophysiological pathways, and outline emerging therapeutic strategies along with their pitfalls.

Childhood idiopathic nephrotic syndrome: recent advancements shaping future guidelines

Childhood idiopathic nephrotic syndrome is an important pediatric kidney disease associated with significant morbidities and even mortality. Several guidelines have been developed to standardize the terminology and patient care among the pediatric nephrology community. Since the publication of these guidelines, there have been major breakthroughs in the disease management and the understanding of underlying pathogenesis through multi-omics investigations, including the identification of anti-nephrin autoantibodies, genetic susceptibility loci, and the pathogenic role of B cell subsets. In this educational review, we summarize the recent major advancements in idiopathic nephrotic syndrome and attempt to provide potential therapeutic approaches in both steroid-sensitive and steroid-resistant nephrotic syndrome that may shape future guideline development.

The Pathogenesis of Nephrotic Syndrome: A Perspective from B Cells

Background

Nephrotic syndrome is a special type of chronic kidney disease, the specific pathogenesis of which remains unclear. An increasing number of studies have suggested that B cells play an important role in the pathogenesis of nephrotic syndrome.

Summary

Idiopathic nephrotic syndrome is a common kidney disease in children. While previously believed to be primarily caused by T-cell disorders, recent research has shifted its focus to B cells. Studies have shown that B cells play a significant role in the pathogenesis of NS, potentially even more so than T cells. This article provides a comprehensive review of the involvement of B cells in the development of idiopathic nephrotic syndrome.

Key Messages

B cells are involved in the pathogenesis of nephrotic syndrome by producing autoantibodies and various cytokines.

Post-transplant glomerular diseases: update on pathophysiology, risk factors and management strategies

In recent years, advancements in immunosuppressive medications and post-transplant management have led to a significant decrease in acute rejection rates in renal allografts and consequent improvement in short-term graft survival. In contrast, recent data have shown an increased incidence of post-transplant glomerular diseases, which currently represent a leading cause of allograft loss. Although pathogenesis is not fully understood, growing evidence supports the role of inherited and immunological factors and has identified potential pre- and post-transplant predictors. In this review, we illustrate recent advancements in the pathogenesis of post-transplant glomerular disease and the role of risk factors and immunological triggers. In addition, we discuss potential prevention and management strategies.

Anti-slit diaphragm antibodies on kidney biopsy identify pediatric patients with steroid-resistant nephrotic syndrome responsive to second-line immunosuppressants

Podocytopathies represent a group of glomerular disorders associated with minimal changes (MC) or focal segmental glomerulosclerosis (FSGS) lesion patterns at biopsy and heterogeneous responses to steroids. Anti-nephrin antibodies were previously found in such patients, suggesting an autoimmune form of podocytopathy. High resolution confocal microscopy on kidney biopsies of a cohort of 128 pediatric patients revealed localization of IgG along the slit diaphragm in 30% of patients with MC and 25% of those with FSGS, but not in other lesion patterns. Anti-nephrin IgG ELISA assay in the serum and stimulated emission depletion microscopy of kidney biopsies showed IgG-nephrin co-localization only in 77.8% of cases. Similar observations were obtained in a cohort of 48 adult patients with MC or FSGS at kidney biopsy, where IgG-nephrin colocalization was only 44.4%, suggesting the existence of autoantibodies binding to other slit proteins. Patients with anti-slit antibodies showed nephrotic syndrome at onset in 94.4% of cases. Patients with primary steroid-resistance had anti-slit antibodies in 27%, while those with secondary steroid-resistance in 87.5% of cases, irrespective of the histopathological lesion pattern. Steroid-resistant patients with anti-slit antibodies responded to second-line immunosuppressants in 92.3% vs. only 20% of patients that were anti-slit negative. No patient with anti-slit antibodies developed kidney failure vs. 51.7% of those negative for antibodies (66.7% with a genetic cause and 41.2% with a non-genetic cause). Thus, the detection of anti-slit antibodies can identify patients with an autoimmune podocytopathy responsive to treatment with second-line immunosuppressants, irrespective of the histopathological lesion pattern at biopsy.

Technology Innovation for Discovering Renal Autoantibodies in Autoimmune Conditions

Autoimmune glomerulonephritis is a homogeneous area of renal pathology with clinical relevance in terms of its numerical impact and difficulties in its treatment. Systemic lupus erythematosus/lupus nephritis and membranous nephropathy are the two most frequent autoimmune conditions with clinical relevance. They are characterized by glomerular deposition of circulating autoantibodies that recognize glomerular antigens. Technologies for studying renal tissue and circulating antibodies have evolved over the years and have culminated with the direct analysis of antigen-antibody complexes in renal bioptic fragments. Initial studies utilized renal microdissection to obtain glomerular tissue. Obtaining immunoprecipitates after partial proteolysis of renal tissue is a recent evolution that eliminates the need for tissue microdissection. New technologies based on 'super-resolution microscopy' have added the possibility of a direct analysis of the interaction between circulating autoantibodies and their target antigens in glomeruli. Peptide and protein arrays represent the new frontier for identifying new autoantibodies in circulation. Peptide arrays consist of 7.5 million aligned peptides with 16 amino acids each, which cover the whole human proteome; protein arrays utilize, instead, a chip containing structured proteins, with 26.000 overall. An example of the application of the peptide array is the discovery in membranous nephropathy of many new circulating autoantibodies including formin-like-1, a protein of podosomes that is implicated in macrophage movements. Studies that utilize protein arrays are now in progress and will soon be published. The contribution of new technologies is expected to be relevant for extending our knowledge of the mechanisms involved in the pathogenesis of several autoimmune conditions. They may also add significant tools in clinical settings and modify the therapeutic handling of conditions that are not considered to be autoimmune.

Podocyte-targeted therapies - progress and future directions

Podocytes are the key target cells for injury across the spectrum of primary and secondary proteinuric kidney disorders, which account for up to 90% of cases of kidney failure worldwide. Seminal experimental and clinical studies have established a causative link between podocyte depletion and the magnitude of proteinuria in progressive glomerular disease. However, no substantial advances have been made in glomerular disease therapies, and the standard of care for podocytopathies relies on repurposed immunosuppressive drugs. The past two decades have seen a remarkable expansion in understanding of the mechanistic basis of podocyte injury, with prospects increasing for precision-based treatment approaches. Dozens of disease-causing genes with roles in the pathogenesis of clinical podocytopathies have been identified, as well as a number of putative glomerular permeability factors. These achievements, together with the identification of novel targets of podocyte injury, the development of potential approaches to harness the endogenous podocyte regenerative potential of progenitor cell populations, ongoing clinical trials of podocyte-specific pharmacological agents and the development of podocyte-directed drug delivery systems, contribute to an optimistic outlook for the future of glomerular disease therapy.

Anti-nephrin autoantibodies: novel predictors of post-transplant recurrence of focal segmental glomerular sclerosis

Post-transplant recurrence of focal segmental glomerular sclerosis (FSGS) is a major challenge in the field of kidney transplantation. Currently, the most reliable predictor of FSGS recurrence is disease recurrence in a previous allograft. Recent studies suggest a possible causal role of anti-nephrin autoantibodies in the primary disease (primary FSGS and minimal change disease), as well as post-transplant recurrence of FSGS. In this issue of Kidney International, Batal et al. evaluate pretransplant anti-nephrin autoantibodies as a specific predictor of FSGS recurrence and demonstrate colocalization of nephrin and punctate IgG in anti-nephrin-positive patients with disease recurrence.

Potential biomarkers of recurrent FSGS: a review

Focal segmental glomerulosclerosis (FSGS), a clinicopathological condition characterized by nephrotic-range proteinuria, has a high risk of progression to end-stage renal disease (ESRD). Meanwhile, the recurrence of FSGS after renal transplantation is one of the main causes of graft loss. The diagnosis of recurrent FSGS is mainly based on renal puncture biopsy transplants, an approach not widely consented by patients with early mild disease. Therefore, there is an urgent need to find definitive diagnostic markers that can act as a target for early diagnosis and intervention in the treatment of patients. In this review, we summarize the domestic and international studies on the pathophysiology, pathogenesis and earliest screening methods of FSGS and describe the functions and roles of specific circulating factors in the progression of early FSGS, in order to provide a new theoretical basis for early diagnosis of FSGS recurrence, as well as aid the exploration of therapeutic targets.

A randomised, two-arm (1:1 ratio), double blind, placebo controlled phase III trial to assess the efficacy, safety, cost and cost-effectiveness of Rituximab in treating de novo or relapsing NS in patients with MCD/FSGS (TURING)

BACKGROUND

Minimal Change Disease (MCD) and Focal Segmental Glomerulosclerosis (FSGS) are a spectrum of disease causing the nephrotic syndrome (NS), characterised by proteinuria with debilitating oedema, as well as a high risk of venous thromboembolic disease and infection. Untreated, 50-60% patients with FSGS progress to end stage kidney disease after 5 years. These diseases respond to immunosuppression with high dose glucocorticoids, but 75% will relapse as the glucocorticoids are withdrawn, leading to significant morbidity associated with prolonged use. In children, the B cell depleting monoclonal antibody rituximab reduces relapse risk, but this drug has not been tested in randomised controlled trial in adults.

METHODS

130-150 adults with new or relapsing MCD/FSGS, from UK Renal Units, are being randomised to receive either rituximab (two 1 g infusions two weeks apart) or placebo. Partipicipants are recruited when they present with nephrosis, and all are treated with glucocorticoids as per KDIGO guidelines. Once in remission, prednisolone is withdrawn according to a pre-specified regimen. If in remission at 6 months, participants receive a further dose of trial drug. If they relapse, they are unblinded, and if they have received placebo, they are offered open label rituximab with protocolised prednisolone as in the main phase of the trial. The primary end point is time from remission to relapse. A number of secondary endpoints will be assessed including the effect of rituximab on: (1) NHS and societal resource use and hence cost: (2) safety: (3) other measures of efficacy, such as achievement of partial and complete remission of NS and the preservation of renal function: (4) health status of participant.

TRIAL REGISTRATION

TURING received ethical approval on 14 Jun 2019 - REC reference: 19/LO/0738. It is registered on EudraCT, with ID number: 2018-004611-50, with a start date of 2019-06-14.

Autoantibodies Targeting Nephrin in Podocytopathies

BACKGROUND

Minimal change disease and primary focal segmental glomerulosclerosis in adults, along with idiopathic nephrotic syndrome in children, are immune-mediated podocytopathies that lead to nephrotic syndrome. Autoantibodies targeting nephrin have been found in patients with minimal change disease, but their clinical and pathophysiological roles are unclear.

METHODS

We conducted a multicenter study to analyze antinephrin autoantibodies in adults with glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, antineutrophil cytoplasmic antibody-associated glomerulonephritis, and lupus nephritis, as well as in children with idiopathic nephrotic syndrome and in controls. We also created an experimental mouse model through active immunization with recombinant murine nephrin.

RESULTS

The study included 539 patients (357 adults and 182 children) and 117 controls. Among the adults, antinephrin autoantibodies were found in 46 of the 105 patients (44%) with minimal change disease, 7 of 74 (9%) with primary focal segmental glomerulosclerosis, and only in rare cases among the patients with other conditions. Of the 182 children with idiopathic nephrotic syndrome, 94 (52%) had detectable antinephrin autoantibodies. In the subgroup of patients with active minimal change disease or idiopathic nephrotic syndrome who were not receiving immunosuppressive treatment, the prevalence of antinephrin autoantibodies was as high as 69% and 90%, respectively. At study inclusion and during follow-up, antinephrin autoantibody levels were correlated with disease activity. Experimental immunization induced a nephrotic syndrome, a minimal change disease-like phenotype, IgG localization to the podocyte slit diaphragm, nephrin phosphorylation, and severe cytoskeletal changes in mice.

CONCLUSIONS

In this study, circulating antinephrin autoantibodies were common in patients with minimal change disease or idiopathic nephrotic syndrome and appeared to be markers of disease activity. Their binding at the slit diaphragm induced podocyte dysfunction and nephrotic syndrome, which highlights their pathophysiological significance. (Funded by Deutsche Forschungsgemeinschaft and others.).

Clinical Course of Nonresponders With Recurrent Focal Segmental Glomerulosclerosis After Pediatric Kidney Transplantation: A Retrospective Multicenter Study

BACKGROUND

Primary focal segmental glomerulosclerosis (FSGS) frequently recurs after kidney transplantation and is associated with poor graft survival. Patients who do not achieve remission (nonresponders) have an especially poor graft survival. However, the characteristics that may affect graft survival in nonresponders are unknown. This study aimed to determine the clinical characteristics associated with graft survival in nonresponders.

METHODS

We retrospectively collected the clinical records of patients with FSGS and an age at onset <16 years who experienced posttransplant recurrence of FSGS at six hospitals in Japan from 1993 to 2018.

RESULTS

Eight nonresponders with recurrent FSGS were enrolled in this study. The median time to recurrence after kidney transplantation was 1 day (interquartile range, 1-2 days). All patients received therapeutic plasma exchange and methylprednisolone pulse therapy. Rituximab was used as an add-on therapy in three patients. Five patients lost their graft within 2 years after kidney transplantation (rapid group). In contrast, three patients had much longer graft survival (nonrapid group). We compared the clinical characteristics of the rapid and nonrapid groups. Proteinuria tended to be lower in the nonrapid group at the third and subsequent months of therapy. The rapid group had persistent nephrotic syndrome. The rate of reduction in proteinuria was lower in the rapid group than in the nonrapid group.

CONCLUSIONS

Our study suggests that persistent nephrotic syndrome and a low rate of reduction in proteinuria may predict rapid progression to graft failure in nonresponders.

Evaluation of Methodologies in Anti-nephrin Autoantibody Detection

Recent studies discovered the prominent presence of anti-nephrin autoantibodies in minimal change disease, steroid-sensitive nephrotic syndrome and/or post-transplant recurrent focal segmental glomerulosclerosis (FSGS). However, widely different, and often unconventional autoantibody detection methods were used among these studies, making it challenging to assess the pathogenic role for the antibodies. Here we examined methods of conventional ELISA, magnetic on-beads ELISA, immunoprecipitation-immunoblotting (IP-IB), and cell- and tissue-based antibody assays with 127 plasma samples of kidney and non-kidney diseases. On the antigen side, we compared commercially available recombinant human nephrin extracelluar domain (ECD) produced from human or mouse cell lines, as well as lab-made full length, ECD, and series of ECD truncates for measuring autoantibody reactivity and specificity. Surprisingly, different assay methods and different antigen preparations led to observation of assay-specific false-positive and false-negative results. In general, a set of tests that combines magnetic beads-enhanced ELISA, followed by IP-IB, and epitope mapping showed the most robust results for anti-nephrin autoantibodies, detected in two primary FSGS patients among all cases tested. It is interesting to note that cell/tissue-based results, also supported by antigen truncation studies, clearly suggest steric hindrance of reactive epitopes, as in full length nephrin that forms compact self-associated complexes. In conclusion, anti-nephrin positivity is rare among the tested patients (2/127), including those with FSGS (2/42), and autoantibody results can be affected by the choice of detection methods.

Anti-nephrin antibodies in recurrence of focal segmental glomerulosclerosis: closer to discovering the Holy Grail?

Recurrent forms of primary focal segmental glomerulosclerosis (FSGS) pose an unmet challenge to nephrologists, both in terms of understanding the underlying pathophysiology and in terms of identifying an effective management strategy of this disease, which frequently leads to kidney graft loss. In the past few decades, experimental observations both in patients and in animal models have led to the hypothesis of the existence of circulating factors driving the loss of integrity of the glomerular filtration barrier in FSGS. Although different circulating factor candidates have been postulated, none has been unequivocally shown to be pathogenic. In the current study, Shirai et al. propose a new candidate for this role by identifying circulating anti-nephrin autoantibodies in a cohort of patients with post-transplant recurrence of primary FSGS. Recent evidence by Watts et al. has also identified anti-nephrin autoantibodies in the circulation and in the kidney biopsies of patients with minimal change disease. If confirmed, the identification of these autoantibodies would both contribute to identifying the elusive circulating factor in FSGS and increase our understanding of the spectrum of proteinuric glomerular lesions, spanning from minimal change disease to FSGS. The quest for the Holy Grail is perhaps closer to completion.

Immunofluorescence Use and Techniques in Glomerular Diseases: A Review

Background

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

Summary

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

Key Messages

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