Clinico-pathological correlations of congenital and infantile nephrotic syndrome over twenty years

NPHS Mutations in Pediatric Patients with Congenital and Steroid-Resistant Nephrotic Syndrome

NPHS1 and NPHS2 are kidney gene components that encode for nephrin and podocin, respectively. They play a role in the progression of congenital (CNS) and steroid-resistant (SRNS) nephrotic syndrome. Hence, this study aimed to determine the prevalence and renal outcomes of NPHS mutations among pediatric patients with CNS and SRNS. We also aimed to identify potential predictors of NPHS mutations in this patient cohort. Overall, this study included 33 studies involving 2123 patients screened for NPHS1, whereas 2889 patients from 40 studies were screened for NPHS2 mutations. The patients' mean age was 4.9 ± 1 years (ranging from birth to 18 years), and 56% of patients were male (n = 1281). Using the random-effects model, the pooled proportion of NPHS1 mutations among pediatric patients with CNS and SRNS was 0.15 (95% CI 0.09; 0.24, p < 0.001, I2 = 92.0%). The pooled proportion of NPHS2 mutations was slightly lower, at 0.11 (95% CI 0.08; 0.14, p < 0.001, I2 = 73.8%). Among the 18 studies that reported ESRF, the pooled proportion was 0.47 (95% CI 0.34; 0.61, p < 0.001, I2 = 75.4%). Our study showed that the NPHS1 (β = 1.16, p = 0.35) and NPHS2 (β = 5.49, p = 0.08) mutations did not predict ESRF in CNS and SRNS pediatric patients. Nevertheless, patients from the European continent who had the NPHS2 mutation had a significantly higher risk of developing ESRF (p < 0.05, β = 1.3, OR = 7.97, 95% CI 0.30; 2.30) compared to those who had the NPHS1 mutation. We recommend NPHS mutation screening for earlier diagnosis and to avoid unnecessary steroid treatments. More data are needed to better understand the impact of NPHS mutations among pediatric patients with CNS and SRNS.

Late nephrectomy in infants with congenital nephrotic syndrome of the Finnish type

AIM

Bilateral nephrectomy is commonly performed in patients with congenital nephrotic syndrome of the Finnish type. The optimal timing of nephrectomy is unclear.

METHODS

Growth, thromboembolic events, infections, transplant-related complications and ability to eat were compared between infants with early (Group 1, n = 13) and late (Group 2, n = 10) nephrectomy. 'Early' was defined as nephrectomy at 7-kg body weight followed by peritoneal dialysis and 'late' as nephrectomy at ≥10 kg followed by 3-4 weeks of haemodialysis and kidney transplantation. Patients were followed until the end of the first post-transplant year.

RESULTS

Dialysis time was significantly longer in group 1 than in group 2. Late nephrectomy did not increase the risk for thromboembolic events or septicaemia but decreased tube feeding dependency (group 1 69% vs. group 2 20%, p = 0.019). Motor development at transplantation was considered normal in 80% of the infants with late nephrectomy compared to 31% in the early nephrectomy group (p = 0.019); however, the difference between the groups disappeared by the end of the follow-up.

CONCLUSION

Infants with late nephrectomy have comparative outcome but less feeding tube dependency and better motor development during the first post-transplant months compared to infants with early nephrectomy.

Genetic Susceptibility to Chronic Kidney Disease: Links, Risks and Management

Chronic kidney disease (CKD) is associated with significant morbidity and mortality worldwide. In recent years, our understanding of genetic causes of CKD has expanded significantly with several renal conditions having been identified. This review discusses the current landscape of genetic kidney disease and their potential treatment options. This review will focus on cystic kidney disease, glomerular disease with genetic associations, congenital anomalies of kidneys and urinary tract (CAKUT), autosomal dominant-tubulointerstitial kidney disease (ADTKD), inherited nephrolithiasis and nephrocalcinosis.

Case Report: CMV-Associated Congenital Nephrotic Syndrome

Background: Congenital nephrotic syndrome, historically defined by the onset of large proteinuria during the first 3 months of life, is a rare clinical disorder, generally with poor outcome. It is caused by pathogenic variants in genes associated with this syndrome or by fetal infections disrupting podocyte and/or glomerular basement membrane integrity. Here we describe an infant with congenital CMV infection and nephrotic syndrome that failed to respond to targeted antiviral therapy. Case and literature survey highlight the importance of the "tetrad" of clinical, virologic, histologic, and genetic workup to better understand the pathogenesis of CMV-associated congenital and infantile nephrotic syndromes. Case Presentation: A male infant was referred at 9 weeks of life with progressive abdominal distention, scrotal edema, and vomiting. Pregnancy was complicated by oligohydramnios and pre-maturity (34 weeks). He was found to have nephrotic syndrome and anemia, normal platelet and white blood cell count, no splenomegaly, and no syndromic features. Diagnostic workup revealed active CMV infection (positive CMV IgM/PCR in plasma) and decreased C3 and C4. Maternal anti-CMV IgG was positive, IgM negative. Kidney biopsy demonstrated focal mesangial proliferative and sclerosing glomerulonephritis with few fibrocellular crescents, interstitial T- and B-lymphocyte infiltrates, and fibrosis/tubular atrophy. Immunofluorescence was negative. Electron microscopy showed diffuse podocyte effacement, but no cytomegalic inclusions or endothelial tubuloreticular arrays. After 4 weeks of treatment with valganciclovir, plasma and urine CMV PCR were negative, without improvement of the proteinuria. Unfortunately, the patient succumbed to fulminant pneumococcal infection at 7 months of age. Whole exome sequencing and targeted gene analysis identified a novel homozygous, pathogenic variant (2071+1G>T) in NPHS1. Literature Review and Discussion: The role of CMV infection in isolated congenital nephrotic syndrome and the corresponding pathological changes are still debated. A search of the literature identified only three previous reports of infants with congenital nephrotic syndrome and evidence of CMV infection, who also underwent kidney biopsy and genetic studies. Conclusion: Complete workup of congenital infections associated with nephrotic syndrome is warranted for a better understanding of their pathogenesis ("diagnostic triad" of viral, biopsy, and genetic studies). Molecular testing is essential for acute and long-term prognosis and treatment plan.

Diagnostic and Management Challenges in Congenital Nephrotic Syndrome

Congenital Nephrotic Syndrome (CNS) is defined as nephrotic range proteinuria, hypoalbuminaemia and edema in the first three months of life. CNS is most commonly genetic in cause, with international variance in the incidence of causative mutations. Initially defined by the histopathological appearance, increasingly sophisticated and accessible genetic analyses now provide a body of evidence to suggest that there is a disparity between the histological appearance, the genotype of individuals and the severity of the clinical disease. Through the evolution of management approaches CNS has changed from being an invariably fatal condition to one with appreciable ongoing morbidity and mortality but comparably good outcomes to other causes of paediatric end-stage renal disease, especially following transplantation. This review briefly summarises the more commonly recognised genetic mutations leading to CNS, addresses common management decisions, and concludes with potential therapies for the future.

Genetics of congenital and infantile nephrotic syndrome

BACKGROUND

Congenital and infantile nephrotic syndrome (CNS and INS) are rare inherited defects in glomerular filtration involving a variety of gene mutations. This study aimed to analyze all genetic mutations associated with congenital and infantile nephrotic syndrome treated at our institution. We also discussed our different approach secondary to culture and resources.

METHODS

A retrospective single-center study of all children diagnosed as NS before the age of 1 year over a duration of over one decade.

RESULTS

Twenty-nine children (12 boys) were included in the study. Their median age (range) was 2.4 (0.1-12) months (20 CNS and 9 INS). Consanguinity was present in 90% of children. The genetic analysis' results were only available for 20 children. An underlying causative homozygous mutation was detected in 18 children (90%): NPHS1 (9), NPHS2(2), LAMB2(3), PLCE1(1), WT1(1), and ITSN1 novel mutation (2). One child had heterozygous mutation of NPHS2 and another child had heterozygous mutation of NPHS1 which could not explain the disease. All CNS cases were all managed with intermittent intravenous albumin infusion, ACEi, diuretics, and indomethacin. None of the children were managed by nephrectomy followed by peritoneal dialysis (PD) because of limited resources. Only one child achieved partial remission, while 15 children died at a median (range) age of 5.8 (1.25-29) months. The remaining 14 children were followed up for an average of 36 (3.9-120) months. Three children progressed to end-stage kidney disease and PD was performed in only two children.

CONCLUSIONS

NPHS1 is the main underlying cause of CNS and INS in our study population. CNS and INS were associated with high morbidity and mortality.

Nephrotic Syndrome

Nephrotic syndrome is characterized by edema, proteinuria, hypoalbuminemia, and hyperlipidemia. Minimal change disease, the most common cause in childhood, generally responds to corticosteroids, although most patients experience disease relapses. Focal segmental glomerulosclerosis is usually resistant to corticosteroids and carries a significant risk of kidney failure, necessitating renal transplantation. Nephrotic syndrome may also be secondary to gene mutations and systemic diseases such as lupus. Clinical evaluation involves distinguishing primary and secondary causes and monitoring for disease complications, including blood clots and serious infections such as spontaneous bacterial peritonitis. Immunosuppressive medications are used to prevent relapses and treat corticosteroid-resistant disease.

Cyclosporine A responsive congenital nephrotic syndrome with single heterozygous variants in NPHS1, NPHS2, and PLCE1

BACKGROUND

Congenital nephrotic syndrome (CNS) is primarily a monogenetic disease, with the majority of cases due to changes in five different genes: the nephrin (NPHS1), podocin (NPHS2), Wilms tumor 1 (WT1), laminin ß2 (LAMB2), and phospholipase C epsilon 1 (PLCE1, NPHS3) gene. Usually CNS is not responsive to immunosuppressive therapy, but treatment with ACE inhibitors, AT1 receptor blockade and/or indomethacin can reduce proteinuria. If the disease progresses to end-stage renal disease, kidney transplantation is the therapy of choice.

CASE-DIAGNOSIS

Here, we present the case of a 4-month-old girl with congenital nephrotic syndrome. Upon admission, the patient presented with life-threatening anasarca, hypoalbuminemia, proteinuria, and impaired growth. There was no evidence of an infectious or immunological etiology. The genetic evaluation revealed a heterozygous variant in NPHS1 (p.Arg207Trp), in NPHS2 (p.Ser95Phe) as well as in PLCE1 (p.Ala1045Ser) and did not explain CNS. In addition to daily parenteral albumin infusions plus furosemide, a pharmacological antiproteinuric therapy was started to reduce protein excretion. Based on the genetic results, immunosuppressive therapy with prednisolone was initiated, but without response. However, following cyclosporine A treatment, the patient achieved complete remission and now has good renal function, growth, and development.

CONCLUSIONS

A profound search for the cause of CNS is necessary but has its limitations. The therapeutic strategy should be adapted when the etiology remains unclear.

Analysis of 24 genes reveals a monogenic cause in 11.1% of cases with steroid-resistant nephrotic syndrome at a single center

BACKGROUND

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of end-stage renal disease (ESRD) among patients manifesting at under 25 years of age. We performed mutation analysis using a high-throughput PCR-based microfluidic technology in 24 single-gene causes of SRNS in a cohort of 72 families, who presented with SRNS before the age of 25 years.

METHODS

Within an 18-month interval, we obtained DNA samples, pedigree information, and clinical information from 77 consecutive children with SRNS from 72 different families seen at Boston Children's Hospital (BCH). Mutation analysis was completed by combining high-throughput multiplex PCR with next-generation sequencing. We analyzed the sequences of 18 recessive and 6 dominant genes of SRNS in all 72 families for disease-causing variants.

RESULTS

We identified the disease-causing mutation in 8 out of 72 (11.1%) families. Mutations were detected in the six genes: NPHS1 (2 out of 72), WT1 (2 out of 72), NPHS2, MYO1E, TRPC6, and INF2. Median age at onset was 4.1 years in patients without a mutation (range 0.5-18.8), and 3.2 years in those in whom the causative mutation was detected (range 0.1-14.3). Mutations in dominant genes presented with a median onset of 4.5 years (range 3.2-14.3). Mutations in recessive genes presented with a median onset of 0.5 years (range 0.1-3.2).

CONCLUSION

Our molecular genetic diagnostic study identified underlying monogenic causes of steroid-resistant nephrotic syndrome in ~11% of patients with SRNS using a cost-effective technique. We delineated some of the therapeutic, diagnostic, and prognostic implications. Our study confirms that genetic testing is indicated in pediatric patients with SRNS.

Advances in renal genetic diagnosis

Most genetic disorders are clinically and genetically heterogeneous. Next-generation sequencing (NGS) has revolutionized the field and is providing rapidly growing insights into the pathomechanism of hereditary nephropathies. Current best-practice guidelines for most hereditary nephropathies include genetic diagnostics. The increasing number of genes that have to be considered in patients with hereditary nephropathies is often challenging when addressed by conventional techniques and largely benefits from NGS-based approaches that allow the parallel analysis of all disease genes in a single test at relatively low cost, e.g., by the use of multi-gene panels. Knowledge of the underlying genotype is of advantage in discussions with regard to transplantation and therapeutic options. Further, genetics may aid the early detection and treatment of renal and extrarenal complications and the reduction of invasive procedures. An accurate genetic diagnosis is crucial for genetic counselling, provides information about the recurrence risk and may help to improve the clinical management of patients and their families. The bottleneck in genetics is no longer the primary wet lab process but the interpretation of the obtained genetic data, which is by far the most challenging and work-intensive part of the analysis. This can only be managed in a multidisciplinary setting that brings together expert knowledge in genetics and the respective medical field. In the future, bench and bedside benefits can be expected from this kind of digitized medicine.

Genetics of hereditary nephrotic syndrome: a clinical review

Advances in podocytology and genetic techniques have expanded our understanding of the pathogenesis of hereditary steroid-resistant nephrotic syndrome (SRNS). In the past 20 years, over 45 genetic mutations have been identified in patients with hereditary SRNS. Genetic mutations on structural and functional molecules in podocytes can lead to serious injury in the podocytes themselves and in adjacent structures, causing sclerotic lesions such as focal segmental glomerulosclerosis or diffuse mesangial sclerosis. This paper provides an update on the current knowledge of podocyte genes involved in the development of hereditary nephrotic syndrome and, thereby, reviews genotype-phenotype correlations to propose an approach for appropriate mutational screening based on clinical aspects.

The etiology of congenital nephrotic syndrome: current status and challenges

BACKGROUND

Congenital nephrotic syndrome (CNS), defined as heavy proteinuria, hypoalbuminemia, hyperlipidemia and edema presenting in the first 0-3 months of life, may be caused by congenital syphilis, toxoplasmosis, or congenital viral infections (such as cytomegalovirus). However, the majority of CNS cases are caused by monogenic defects of structural proteins that form the glomerular filtration barrier in the kidneys. Since 1998, an increasing number of genetic defects have been identified for their involvements in the pathogenesis of CNS, including NPHS1, NPHS2, WT1, PLCE1, and LAMB2.

DATA SOURCES

We searched databases such as PubMed, Elsevier and Wanfang with the following key words: congenital nephrotic syndrome, proteinuria, infants, neonate, congenital infection, mechanism and treatment; and we selected those publications written in English that we judged to be relevant to the topic of this review.

RESULTS

Based on the data present in the literature, we reviewed the following topics: 1) Infection associated CNS including congenital syphilis, congenital toxoplasmosis, and congenital cytomegalovirus infection; 2) genetic CNS including mutation of NPHS1 (Nephrin), NPHS2 (Podocin), WT1, LAMB2 (Laminin-β2), PLCE1 (NPHS3); 3) Other forms of CNS including maternal systemic lupus erythematosus, mercury poisoning, renal vein thrombosis, neonatal alloimmunization against neutral endopeptidase.

CONCLUSION

At present, the main challenge in CNS is to identify the cause of disease for individual patients. To make a definitive diagnosis, with the exclusion of infection-related CNS and maternal-associated disorders, pathology, family history, inheritance mode, and other accompanying congenital malformations are sometimes, but not always, useful indicators for diagnosing genetic CNS. Next-generation sequencing would be a more effective method for diagnosing genetic CNS in some patients, however, there are still some challenges with next-generation sequencing that need to be resolved in the future.

Disease-causing mutations of RhoGDIα induce Rac1 hyperactivation in podocytes

Nephrotic syndrome (NS) describes a group of kidney disorders in which there is injury to podocyte cells, specialized cells within the kidney's glomerular filtration barrier, allowing proteins to leak into the urine. Three mutations in ARHGDIA, which encodes Rho GDP dissociation inhibitor α (GDIα), have been reported in patients with heritable NS and encode the following amino acid changes: ΔD185, R120X, and G173V. To investigate the impact of these mutations on podocyte function, endogenous GDIα was knocked-down in cultured podocytes by shRNA and then the cells were re-transfected with wild-type or mutant GDIα constructs. Among the 3 prototypical Rho-GTPases, Rac1 was markedly hyperactivated in podocytes with any of the 3 mutant forms of GDIα while the activation of RhoA and Cdc42 was modest and variable. All three mutant GDIα proteins resulted in slow podocyte motility, suggesting that podocytes are sensitive to the relative balance of Rho-GTPase activity. In ΔD185 podocytes, both random and directional movements were impaired and kymograph analysis of the leading edge showed increased protrusion and retraction of leading edge (phase switching). The mutant podocytes also showed impaired actin polymerization, smaller cell size, and increased cellular projections. In the developing kidney, GDIα expression increased as podocytes matured. Conversely, active Rac1 was detected only in immature, but not in mature, podocytes. The results indicate that GDIα has a critical role in suppressing Rac1 activity in mature podocytes, to prevent podocyte injury and nephrotic syndrome.

Domiciliary administration of intravenous albumin in congenital nephrotic syndrome

BACKGROUND

Early management of congenital nephrotic syndrome invariably includes the frequent administration of intravenous human albumin solution. The safety and feasibility of intravenous administration of albumin in the patients' home setting has not previously been reported.

CASE-DIAGNOSIS/TREATMENT

We report a series of seven paediatric patients whose parents were trained in the administration of albumin via a central venous catheter at home, with the aim of minimising hospital admission or attendances. We describe the clinical course of these patients and complication rates ascribed to this strategy.

CONCLUSIONS

Our results demonstrate that home albumin infusion can be performed safely.