NPHS2 Mutations Research Articles

#1118 Direct delivery of novel gene therapy to podocytes enables pathway to clinical translation for the treatment of glomerular diseases

Abstract Background and Aims Adeno associated vector (AAV) gene therapy has the potential to treat a wide range of kidney diseases via the targeted delivery of genes to kidney cells to repair cellular and renal function. Despite the potential to impact many kidney conditions, kidney AAV gene therapy has proven challenging due to technical and physiological hurdles limiting the ability of AAV to be effectively delivered to podocytes. We have developed a novel AAV gene therapy, PS-001, and local method of administration, to effectively and safely deliver the podocin gene NPHS2 to podocytes. Biallelic NPHS2 mutations are the most common cause of monogenic childhood nephrotic syndrome. Curative efficacy and resolution of disease phenotype was demonstrated in transgenic murine models following PS-001 gene therapy treatment. The potential for translation of this approach to NPHS2 nephropathy patients in the clinic was also demonstrated in pre-clinical studies in Gottingen Minipigs. Method Transgenic murine models representative of NPHS2-driven nephropathy were treated with an AAV gene therapy encoding NPHS2, including a knock in mouse model (Nphs2R140Q/−) which introduces a R140Q mutation in the podocin gene. Mice were assessed for improvement in disease phenotype via analysis of proteinuria, serum albumin, renal histopathology and survival. Mice were treated with an analogue of PS-001, as the PS-001 capsid is not permissive in rodents. Gottingen minipigs were treated with PS-001 and followed for 4 weeks. Clinically relevant doses and a procedure for local administration specifically to the kidney were established. In-life safety assessments from blood and urine were monitored and at study end pig tissues were assessed for podocin biodistribution using multiple assays (qPCR, RT-qPCR, ELISA, RNAScope and IF) and for toxicological effects via histopathological analysis. Results Using our AAV gene therapy platform, which includes a capsid that is highly effective at transducing human podocytes and promoter that drives gene expression specifically in the podocyte, the gene therapy product PS-001 encoding NPHS2 was generated. Using a murine analogue of PS-001, in vivo proof of concept studies in a translationally relevant murine disease model (Nphs2R140Q/−) showed NPHS2 delivery and podocin expression in glomeruli and efficacy in terms of renal function rescue. This was demonstrated by resolution of severe proteinuria (mean ACR ug/mg 6049 ± 2803 vs 192 ± 51 in PS-001 treated animals, n = 11), improved serum albumin (g/L 27.50 ± 3.33 g/L vs 30.75 ± 2.46 in PS-001 treated animals, P = .021) and reduction in glomerulosclerosis (mean sclerosed glomeruli 81% ± 19 vs 18.75% ± 12 in PS-001 treated animals, P < .0001). The methods to translate the approach to the clinical setting using a local administration were established in pigs. Administration of PS-001 resulted in transgene mRNA expression across 89% ± 11% of kidney glomeruli as assessed by RNAScope (n = 3 pigs), and transgene derived podocin could be specifically detected in podocytes as assessed by IF analysis. Using qPCR, RT-PCR and ELISA it was shown that using local administration, podocin gene expression was restricted exclusively to the kidney glomerulus, with gene expression undetectable in off-target organs including the liver. Additional toxicological assessments of renal and other organ function from urine and blood, and post-study histopathological assessments revealed no pre-clinical treatment-related safety concerns. Conclusion We present data showing development of an AAV gene therapy and method of administration for the delivery of transgenes specifically to podocytes. We have shown transgenes can be efficiently targeted to podocytes to replace defective genes or to use the podocyte as a protein factory to modulate glomerular biology. This technology therefore provides an important novel modality for potentially treating a broad range of glomerular disease. PS-001 is being developed as a novel approach to treat steroid resistant nephrotic syndrome caused by mutated NPHS2, and may become the first podocyte targeted gene therapy to enter clinical development.

Genotype/phenotype relationship in mild congenital nephrotic syndrome

Introduction. Congenital nephrotic syndrome (CNS) is a severe disease complicated by hemodynamic instability, infections, thrombosis, growth disorder and progressive renal failure leading to end-stage kidney disease within a few years. The mutations of NPHS1 encoding nephrin is the most common cause of the CNS. The aim of this paper was to present a patient with NPHS1 homozygous Ser350Pro missense mutation that unexpectedly caused a mild clinical course of CNS. Case outline. We present a female patient who was diagnosed with severe nephrotic syndrome at 2.5 months of age. While waiting for the result of the genetic analysis, she was treated unsuccessfully with corticosteroids and angiotensin converting inhibitor (ACEI) four weeks, and then under Cyclosporine A (CsA) and ACEI she achieved partial remission within three months. Initially, the milder clinical course was explained by the positive effect of CsA, but as partial remission persisted even after the discontinuation of this drug, it remains unclear what influenced the improvement of the clinical course of the disease. At the time of writing this paper, the patient was 10.9 years old with normal serum creatinine, normal blood pressure and non-nephrotic proteinuria. Conclusion. NPHS1 homozygous Ser350Pro missense mutation may be presented by a mild clinical course of CNS. Further studies are needed to clarify a more predictive CNS genotype/phenotype relationship.

Pseudotumor Cerebri Following Kidney Transplant

Pseudotumor cerebri (PTC) is a condition characterized by raised intracranial pressure, normal cerebrospinal fluid contents, and normal brain parenchyma on imaging. In this report, we present a 9-year-old boy with a native kidney disease of familial steroid-resistant nephrotic syndrome due to homozygous NPHS2 mutation, who received a kidney allograft from a living-related donor and developed PTC 3 years after transplant. Ongoing medications included mycophenolate mofetil, cyclosporin, and prednisolone as immunosuppressants. This case describes the resolution of PTC after switching to tacrolimus from cyclosporin. Patients who undergo renal transplantation and are on treatment modalities, including cyclosporine, are at risk of PTC, and prompt evaluation and urgent treatment may prevent blindness.

Mutation of NPHS1, NPHS2, WT1, LAMB2, COL4A5 and other genes in children with idiopathic steroid resistant nephrotic syndrome

Background: Many children with idiopathic steroid resistant nephrotic syndrome have been reported worldwide due to mutation of NPHS1, NPHS2, WT1 and LAMB2 genes. This study aimed to determine the frequency of mutation of NPHS1, NPHS2, WT1, LAMB2, COL4A5 and other genes and their association with renal histopathological patterns of idiopathic steroid resistant nephrotic syndrome patients. Methods: This cross-sectional study was conducted on 25 patients with idiopathic steroid resistant nephrotic aged 1-17 years in the Department of Paediatric Nephrology, Bangabandhu Sheikh Mujib Medical University, Bangladesh, from July 2017 to June 2018. Next Generation Sequencing and mutation analysis were performed after DNA extraction from patients' venous blood lymphocytes. Histopathological study of renal tissue was done among 17 patients. Results: A little more than half (56%) of the patients were male. The mean age at the initial attack of nephrotic syndrome was 94.2 months. They mostly had minimal change disease (41%) and IgA nephropathy (12%). One subject had the NPHS2 gene mutation, histopathologically diffuse mesangial proliferative glomerulonephritis, and clinically stage-4 chronic kidney disease. Another subject had the COL4A5 gene mutation and focal segmental glomerulosclerosis. Both were male and had no familial renal disease, consanguinity, or hematuria. Conclusion: Children with idiopathic steroid resistant nephrotic syndrome showed NPHS2 and COL4A5 gene mutations. Histopathologically, they showed diffuse mesangial proliferative glomerulonephritis and focal segmental glomerulosclerosis.

A small molecule chaperone rescues keratin-8 mediated trafficking of misfolded podocin to correct genetic Nephrotic Syndrome

Podocin is a key membrane scaffolding protein of the kidney podocyte essential for intact glomerular filtration. Mutations in NPHS2, the podocin-encoding gene, represent the commonest form of inherited nephrotic syndrome (NS), with early, intractable kidney failure. The most frequent podocin gene mutation in European children is R138Q, causing retention of the misfolded protein in the endoplasmic reticulum. Here, we provide evidence that podocin R138Q (but not wild-type podocin) complexes with the intermediate filament protein keratin 8 (K8) thereby preventing its correct trafficking to the plasma membrane. We have also identified a small molecule (c407), a compound that corrects the Cystic Fibrosis Transmembrane Conductance Regulator protein defect, that interrupts this complex and rescues mutant protein mistrafficking. This results in both the correct localization of podocin at the plasma membrane and functional rescue in both human patient R138Q mutant podocyte cell lines, and in a mouse inducible knock-in model of the R138Q mutation. Importantly, complete rescue of proteinuria and histological changes was seen when c407 was administered both via osmotic minipumps or delivered orally prior to induction of disease or crucially via osmotic minipump two weeks after disease induction. Thus, our data constitute a therapeutic option for patients with NS bearing a podocin mutation, with implications for other misfolding protein disorders. Further studies are necessary to confirm our findings.

Nephrotic Syndrome in a Child with R138Q NPHS2 Mutation

Nephrotic Syndrome in a Child with R138Q NPHS2 Mutation

Genetic testing in focal segmental glomerulosclerosis: in whom and when?

Genetic causes are increasingly recognized in patients with focal segmental glomerulosclerosis (FSGS), but it remains unclear which patients should undergo genetic study. Our objective was to determine the frequency and distribution of genetic variants in steroid-resistant nephrotic syndrome FSGS (SRNS-FSGS) and in FSGS of undetermined cause (FSGS-UC). We performed targeted exome sequencing of 84 genes associated with glomerulopathy in patients with adult-onset SRNS-FSGS or FSGS-UC after ruling out secondary causes. Seventy-six patients met the study criteria; 24 presented with SRNS-FSGS and 52 with FSGS-UC. We detected FSGS-related disease-causing variants in 27/76 patients (35.5%). There were no differences between genetic and non-genetic causes in age, proteinuria, glomerular filtration rate, serum albumin, body mass index, hypertension, diabetes or family history. Hematuria was more prevalent among patients with genetic causes. We found 19 pathogenic variants in COL4A3-5 genes in 16 (29.3%) patients. NPHS2 mutations were identified in 6 (16.2%) patients. The remaining cases had variants affecting INF2, OCRL, ACTN4 genes or APOL1 high-risk alleles. FSGS-related genetic variants were more common in SRNS-FSGS than in FSGS-UC (41.7% vs 32.7%). Four SRNS-FSGS patients presented with NPHS2 disease-causing variants. COL4A variants were the most prevalent finding in FSGS-UC patients, with 12 patients carrying disease-causing variants in these genes. FSGS-related variants were detected in a substantial number of patients with SRNS-FSGS or FSGS-UC, regardless of age of onset of disease or the patient's family history. In our experience, genetic testing should be performed in routine clinical practice for the diagnosis of this group of patients.

Adeno-associated virus gene therapy prevents progression of kidney disease in genetic models of nephrotic syndrome.

Gene therapy for kidney diseases has proven challenging. Adeno-associated virus (AAV) is used as a vector for gene therapy targeting other organs, with particular success demonstrated in monogenic diseases. We aimed to establish gene therapy for the kidney by targeting a monogenic disease of the kidney podocyte. The most common cause of childhood genetic nephrotic syndrome is mutations in the podocyte gene NPHS2, encoding podocin. We used AAV-based gene therapy to rescue this genetic defect in human and mouse models of disease. In vitro transduction studies identified the AAV-LK03 serotype as a highly efficient transducer of human podocytes. AAV-LK03-mediated transduction of podocin in mutant human podocytes resulted in functional rescue in vitro, and AAV 2/9-mediated gene transfer in both the inducible podocin knockout and knock-in mouse models resulted in successful amelioration of kidney disease. A prophylactic approach of AAV 2/9 gene transfer before induction of disease in conditional knockout mice demonstrated improvements in albuminuria, plasma creatinine, plasma urea, plasma cholesterol, histological changes, and long-term survival. A therapeutic approach of AAV 2/9 gene transfer 2 weeks after disease induction in proteinuric conditional knock-in mice demonstrated improvement in urinary albuminuria at days 42 and 56 after disease induction, with corresponding improvements in plasma albumin. Therefore, we have demonstrated successful AAV-mediated gene rescue in a monogenic renal disease and established the podocyte as a tractable target for gene therapy approaches.

290 Idiopathic Renal Phosphaturia With Incidental Finding of NPHS2 Mutation

290 Idiopathic Renal Phosphaturia With Incidental Finding of NPHS2 Mutation

Genetic Studies in Infants with Congenital Nephrotic Syndrome: A Case Series.

Information on the genetic profile of congenital nephrotic syndrome (CNS) from India is scarce. The management of CNS is largely supportive of the setting of developing countries, mainly via the administration of intravenous albumin infusions, angiotensin-converting enzyme inhibitors, and levothyroxine. Inadequate infrastructure and management facilities, including genetic analyses, further hamper the outcome. These infants may progress to end-stage renal disease, and mortality is high in infancy. Here, we report a case series of four infants (aged 14-60 days) with CNS from our center with genetic mutations (including mutations in the NPHS1 and LAMB2 genes) that were not described in previous reports from India. Although responsiveness to enalapril has been documented in anecdotal reports of NPHS1 mutations, our case series of four infants did not exhibit any response to enalapril. Our case series adds to the existing literature regarding the genetic profile of CNS in India.

A zebrafish model of congenital nephrotic syndrome of the Finnish type.

Nephrotic syndrome (NS) is a disease characterized by proteinuria and subsequent hypoalbuminemia, hyperlipidemia and edema due to the defective renal glomerular filtration barrier (GFB). Mutations of NPHS1, encoding NEPHRIN, a podocyte protein essential for normal GFB, cause congenital nephrotic syndrome (CNS) of the Finnish type (CNF), which accounts for about 50% of CNS cases. We generated zebrafish nphs1 mutants by using CRISPR/Cas9. These mutants completely lack nephrin proteins in podocytes and develop progressive peri-orbital and whole-body edema after 5 days post fertilization. Ultra-structurally, loss of nephrin results in absence of slit-diaphragms and progressive foot process effacement in zebrafish pronephric glomeruli, similar to the pathological changes in human CNF patients. Interestingly, some nphs1 mutants are viable to adulthood despite ultra-structural defects in renal glomeruli. Using a reporter line Tg (l-fabp:VDBP-GFP) expressing GFP-tagged vitamin-D-binding protein in the blood plasma, we observed a reduction of intravascular GFP fluorescence in the nphs1 mutants, a hypoalbuminemia-like phenotype. In addition, we detected excretion of GFP by the nphs1 mutants, reminiscent of proteinuria. Therefore, we have demonstrated that the nphs1 mutant zebrafish recapitulate the human NS phenotypes and provide a novel and relevant animal model useful for screening therapeutical agents for this disease.

Human pluripotent stem cell-derived kidney organoids for personalized congenital and idiopathic nephrotic syndrome modeling

ABSTRACTNephrotic syndrome (NS) is characterized by severe proteinuria as a consequence of kidney glomerular injury due to podocyte damage. In vitro models mimicking in vivo podocyte characteristics are a prerequisite to resolve NS pathogenesis. The detailed characterization of organoid podocytes resulting from a hybrid culture protocol showed a podocyte population that resembles adult podocytes and was superior compared with 2D counterparts, based on single-cell RNA sequencing, super-resolution imaging and electron microscopy. In this study, these next-generation podocytes in kidney organoids enabled personalized idiopathic nephrotic syndrome modeling, as shown by activated slit diaphragm signaling and podocyte injury following protamine sulfate, puromycin aminonucleoside treatment and exposure to NS plasma containing pathogenic permeability factors. Organoids cultured from cells of a patient with heterozygous NPHS2 mutations showed poor NPHS2 expression and aberrant NPHS1 localization, which was reversible after genetic correction. Repaired organoids displayed increased VEGFA pathway activity and transcription factor activity known to be essential for podocyte physiology, as shown by RNA sequencing. This study shows that organoids are the preferred model of choice to study idiopathic and congenital podocytopathies.

Effect of combined NPHS2 and ACTN4 variants in the onset and severity of focal segmental glomerulosclerosis

Introduction: Focal segmental glomerulosclerosis (FSGS) can be caused by mutations in the genes NPHS2, ACTN4, TRPC6, and INF2 among others, presenting variable levels of proteinuria, including nephrotic syndrome, that frequently progress to end-stage renal disease (ESRD). The establishment of the genotype-phenotype correlation caused by mutations in genes expressed in the podocyte could contribute to understanding their role in FSGS and to the decision-making in the clinical setting in similar cases. Methods: Genomic DNA was extracted from peripheral blood of the proband, his brother, sister and mother. All the exons of the genes NPHS2, ACTN4, TRPC6, and INF2 were amplified by a polymerase chain reaction, purified, and sequenced by the Sanger method. The presence of variants was evaluated in the proband with FSGS and relatives, reviewed, and annotated using dbSNP and HGMD. Results: In the clinical evaluation, the proband and his brother presented childhood-onset nephrotic syndrome, added with renal biopsies confirming FSGS, which was resistant to steroid and other immunosuppressive drugs, and progressed to ESRD. Both patients showed the variants p.P316S in NPHS2 and p.G894S in ACTN4, as well as the polymorphism p.R229Q in NPHS2, all variants in heterozygosis. Their parents were healthy, and the mother presented only the variant p.P316S in NPHS2 in heterozygosis. Conclusions: The family members with FSGS had a combination of the variants p.P316S and p.R229Q in NPHS2, and p.G894S in ACTN4, shared similar clinical presentation, nephrotic syndrome with onset in late childhood that rapidly progressed to ESRD.

Recurrent hypomagnesemia: an uncommon presentation in congenital nephrotic syndrome caused by NPHS-1 mutation

Congenital nephrotic syndrome (CNS) is a rare inherited disorder arising from defects in the proteins of the cells in the glomerular basement membrane and develops either in utero or at birth. The clinical presentation is the result of massive proteinuria. Here we report an interesting clinical case of boy, with history of multiple admissions with involuntary movements found to have recurrent hypocalcaemia and hypomagnesaemia during each admission. Genetic evaluation (clinical exome sequencing) revealed homozygous deletion at exon 23-25 of NPHS1 (NM_004646.4) gene CNS (Finnish type). Child did not have anasarca. CNS presenting as recurrent hypomagnesaemia with absence of anasarca is very rare occurrence in literature.

Unilateral nephrectomy for young infants with congenital nephrotic syndrome of the Finnish type.

The management of congenital nephrotic syndrome of the Finnish type (CNF) is challenging. It is difficult to withdraw intravenous albumin infusions, resulting in long-term hospitalization. In addition, fatal hypotension after bilateral nephrectomy has been reported. In our center, we have performed unilateral nephrectomy during early infancy. Infants diagnosed with CNF between 2011 and 2020 in our institution were enrolled. We examined the clinical course before and after unilateral nephrectomy and evaluated the effectiveness of this strategy. Seven patients (all showing NPHS1 mutations) were enrolled. All required daily intravenous albumin infusion via central venous catheter (CVC). Unilateral nephrectomy was performed at a median of 76days of age (59-208days). Surgical complications did not occur in any of patients. The mean albumin dose was decreased after unilateral nephrectomy (2.0 vs 0.4g/kg/day; p = 0.02). Intravenous albumin infusion could be withdrawn at a median of 17days, the CVC removed at a median of 21days, and they discharged at a median of 82days after unilateral nephrectomy. Although bacterial infections were noted seven times before unilateral nephrectomy, only one episode occurred after surgery. Four patients initiated peritoneal dialysis at two to three years of age and all of them underwent kidney transplantation thereafter. Unilateral nephrectomy during early infancy may be an effective treatment allowing for withdrawal from albumin infusion, prevention of complications, withdrawal from CVCs and shortening hospital stay for patients with CNF.

Congenital Nephrotic Syndrome and the Heart: Lest We Forget!

We report a 2-month-old girl, presenting with anasarca in the early infancy, and was diagnosed to have congenital nephrotic syndrome. In view of a systolic murmur, echocardiography was done which revealed ostium secundum atrial septal defect and branch pulmonary artery stenosis. Genetic analysis was suggestive of single base pair duplication, resulting into frame shift mutation of NPHS1 (nephrin) gene.

Cholelithiasis in infants with congenital nephrotic syndrome of the Finnish type.

Congenital nephrotic syndrome of the Finnish type (CNF) caused by NPHS1 mutations is a rare disease. Infants with CNF can develop many complications, but hepatobiliary complications are uncommon. CNF is not reported as a risk factor of cholelithiasis, which is also a rare disease in the pediatric population. We herein present the cases of three infants with CNF diagnosed with gallstones among a total of seven children with CNF who were treated between 2010 and 2020 in our hospital. The gestational ages, birth weights, and ages at CNF diagnosis of cases 1, 2, and 3 were 38, 37, and 38weeks; 2450, 2374, and 3120g; and 25, 3, and 31days of age, respectively. Imaging studies at the time of CNF diagnosis revealed asymptomatic gallstones in each of them. Case 1 patient developed incarcerated choledocholithiasis and presented with vomiting, white stool, and critically prolonged coagulation at 7months of age. The gallstones disappeared at 3months of age in case 2, although they remained in cases 1 and 3 at the last observation. Infants with CNF can develop cholelithiasis and should undergo hepatobiliary ultrasonography at the time of diagnosis. Patients with gallstones should be evaluated for signs of potential gallstone incarceration because of the risk of hemorrhagic complications due to cholestasis with subsequent vitamin K deficiency and treatment with anticoagulation agents.

A novel mutation of congenital nephrotic syndrome in a Slovenian child eventually receiving a renal transplant

Congenital nephrotic syndrome (CNS) is a rare disease defined as heavy proteinuria, hypoalbuminemia, hyperlipidemia, and edema presenting in the first three months of life. It is most commonly caused by mutations in the NPHS1 gene associated with nephrotic syndrome type 1, also known as Finnish-type CNS, which is inherited in an autosomal recessive manner. Symptomatic treatment with intravenous albumins, vitamins, minerals, nutritional, and hormonal supplementation and treatment of complications are mandatory. Children refractory to the symptomatic treatment are recommended to undergo nephrectomy and renal replacement therapy, preferably renal transplantation. We report on a child with Finnish type CNS with a NPHS1 mutation, which is the first case confirmed by genetic study in Slovenia. We showed for the first time that homozygous mutation c.2928-3del in the NPHS1 gene caused exon 22 skipping, leading to a truncated protein and Fin-minor phenotype.

Impaired NEPHRIN localization in kidney organoids derived from nephrotic patient iPS cells

Mutations in the NPHS1 gene, which encodes NEPHRIN, cause congenital nephrotic syndrome, resulting from impaired slit diaphragm (SD) formation in glomerular podocytes. We previously reported NEPHRIN and SD abnormalities in the podocytes of kidney organoids generated from patient-derived induced pluripotent stem cells (iPSCs) with an NPHS1 missense mutation (E725D). However, the mechanisms underlying the disease may vary depending on the mutations involved, and thus generation of iPSCs from multiple patients is warranted. Here we established iPSCs from two additional patients with different NPHS1 mutations and examined the podocyte abnormalities in kidney organoids derived from these cells. One patient had truncating mutations, and NEPHRIN was undetectable in the resulting organoids. The other patient had a missense mutation (R460Q), and the mutant NEPHRIN in the organoids failed to accumulate on the podocyte surface to form SD precursors. However, the same mutant protein behaved normally when overexpressed in heterologous cells, suggesting that NEPHRIN localization is cell context-dependent. The localization of another SD-associated protein, PODOCIN, was impaired in both types of mutant organoids in a cell domain-specific manner. Thus, the new iPSC lines and resultant kidney organoids will be useful resources for dissecting the disease mechanisms, as well as for drug development for therapies.

Analysis of the clinical characteristics of arthritis with renal disease caused by a NPHS2 gene mutation.

The co-existence of juvenile idiopathic arthritis (JIA)/rheumatoid arthritis (RA) and focal segmental glomerulosclerosis (FSGS) is rare, and the existence of co-pathogenesis remains unknown. In this study, we analyzed the clinical and gene mutation characteristics of a patient with JIA and FSGS caused by a NPHS2 gene mutation, and evaluated the potential connections between these two diseases. We summarized the clinical manifestations, related examination results, and gene mutation characteristics of the patient who presented at our center and six reported cases of arthritis with renal disease. Most of the cases were polyarticular arthritis with varying degrees of renal damage (hematuria, proteinuria, and renal dysfunction) and different prognoses. Among these patients, two developed end-stage renal disease (ESRD), with one dying as a result, while the other patients had a relatively good prognosis. Patients with a family history of renal disease had a poor prognosis. After excluding occasional factors and drug influences, our analysis indicated the existence of co-pathogenesis of arthritis with renal damage (especially FSGS). NPHS2 mutations might account for the family aggregation. Therefore, evaluation of more clinical cases is necessary to further clarify the underlying co-pathogenesis of these diseases.