Genotype-phenotype associations in WT1 glomerulopathy

Mechanisms of podocyte injury in genetic kidney disease

Glomerular diseases are a leading cause of chronic kidney disease worldwide. Both acquired and hereditary glomerulopathies frequently share a common final disease mechanism: disruption of the glomerular filtration barrier, podocyte injury, and ultimately podocyte death and detachment. Over 70 monogenic causes of proteinuric kidney disease have been identified, and most of these genes are highly expressed in podocytes, regulating key processes such as maintenance of the slit diaphragm, regulation of actin cytoskeleton remodeling, and modulation of downstream transcriptional pathways. Collectively, these are increasingly being referred to as hereditary "podocytopathies," in which podocyte injury is the central feature driving proteinuria and kidney dysfunction. In this review, we provide an overview of the monogenic podocytopathies and discuss the molecular mechanisms by which single-gene defects lead to podocyte injury and ultimately glomerulosclerosis. We review how advances in genomic technology and a better understanding of the cell biological basis of disease have led to the development of more targeted and personalized therapeutic strategies, including an overview of small molecule and gene therapy approaches.

Single-cell transcriptomics identifies aberrant glomerular angiogenic signalling in the early stages of WT1 kidney disease

WT1 encodes a podocyte transcription factor whose variants can cause an untreatable glomerular disease in early childhood. Although WT1 regulates many podocyte genes, it is poorly understood which of them are initiators in disease and how they subsequently influence other cell-types in the glomerulus. We hypothesised that this could be resolved using single-cell RNA sequencing (scRNA-seq) and ligand-receptor analysis to profile glomerular cell-cell communication during the early stages of disease in mice harbouring an orthologous human mutation in WT1 (Wt1R394W/+). Podocytes were the most dysregulated cell-type in the early stages of Wt1R394W/+ disease, with disrupted angiogenic signalling between podocytes and the endothelium, including the significant downregulation of transcripts for the vascular factors Vegfa and Nrp1. These signalling changes preceded glomerular endothelial cell loss in advancing disease, a feature also observed in biopsy samples from human WT1 glomerulopathies. Addition of conditioned medium from murine Wt1R394W/+ primary podocytes to wild-type glomerular endothelial cells resulted in impaired endothelial looping and reduced vascular complexity. Despite the loss of key angiogenic molecules in Wt1R394W/+ podocytes, the pro-vascular molecule adrenomedullin was upregulated in Wt1R394W/+ podocytes and plasma and its further administration was able to rescue the impaired looping observed when glomerular endothelium was exposed to Wt1R394W/+ podocyte medium. In comparative analyses, adrenomedullin upregulation was part of a common injury signature across multiple murine and human glomerular disease datasets, whilst other gene changes were unique to WT1 disease. Collectively, our study describes a novel role for altered angiogenic signalling in the initiation of WT1 glomerulopathy. We also identify adrenomedullin as a proangiogenic factor, which despite being upregulated in early injury, offers an insufficient protective response due to the wider milieu of dampened vascular signalling that results in endothelial cell loss in later disease. © 2024 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Nephrotic Syndrome Throughout Childhood: Diagnosing Podocytopathies From the Womb to the Dorm

The etiologies of podocyte dysfunction that lead to pediatric nephrotic syndrome (NS) are vast and vary with age at presentation. The discovery of numerous novel genetic podocytopathies and the evolution of diagnostic technologies has transformed the investigation of steroid-resistant NS while simultaneously promoting the replacement of traditional morphology-based disease classifications with a mechanistic approach. Podocytopathies associated with primary and secondary steroid-resistant NS manifest as diffuse mesangial sclerosis, minimal change disease, focal segmental glomerulosclerosis, and collapsing glomerulopathy. Molecular testing, once an ancillary option, has become a vital component of the clinical investigation and when paired with kidney biopsy findings, provides data that can optimize treatment and prognosis. This review focuses on the causes including selected monogenic defects, clinical phenotypes, histopathologic findings, and age-appropriate differential diagnoses of nephrotic syndrome in the pediatric population with an emphasis on podocytopathies.

Association of Atypical Hemolytic Uremic Syndrome With Wilms' Tumor 1 Gene Mutations: A Case Series and Literature Review

Atypical hemolytic uremic syndrome (aHUS) is a life‑threatening condition characterized by microangiopathic hemolytic anemia, thrombocytopenia, as well as acute kidney injury (AKI). It can occur primarily due to complement gene mutations or secondary to another underlying condition. Several cases with Wilms' tumor gene 1 (WT1) mutations that presented with aHUS have been reported. Here, we report four cases of children diagnosed with WT1 mutations and presented initially with aHUS. There are two boys and two girls who presented with thrombotic microangiopathy (TMA), high lactate dehydrogenase, fragmented red blood cell (RBCs), and severe hypertension. All of them were anuric from the first presentation. Therapy with C5 inhibitors was initiated immediately and was associated with hematological remission without renal recovery. Renal replacement therapy (RRT) was started for all of the patients. A renal biopsy was conducted on two patients and showed global glomerulosclerosis. A genetic study identified pathogenic mutations in the WT1 gene. Two of the patients became dialysis dependent, and two patients underwent renal transplantation without the recurrence of aHUS. Our case series emphasizes that a diagnosis of WT1 mutation can be considered in children with aHUS with severe renal manifestations without a response to C5 inhibitors and with global glomerulosclerosis on renal biopsy. To our knowledge, this is the first report of a series of cases of WT1 mutations in pediatric patients presenting with clinical manifestation manifestations of aHUS. This unique finding highlights an association between HUS and WT1 mutation.

WT1-related disorders: more than Denys-Drash syndrome

Historically, specific mutations in WT1 gene have been associated with distinct syndromes based on phenotypic characteristics, including Denys-Drash syndrome (DDS), Frasier syndrome (FS), Meacham syndrome, and WAGR syndrome. DDS is classically defined by the triad of steroid-resistant nephrotic syndrome (SRNS) onset in the first year of life, disorders of sex development (DSD), and a predisposition to Wilms tumor (WT). Currently, a paradigm shift acknowledges a diverse spectrum of presentations beyond traditional syndromic definitions. Consequently, the concept of WT1-related disorders becomes more precise. A genotype-phenotype correlation has been established, emphasizing that the location and type of WT1 mutations significantly influence the clinical presentation, the condition severity, and the chronology of patient manifestations. Individuals presenting with persistent proteinuria, with or without nephrotic syndrome, and varying degrees of kidney dysfunction accompanied by genital malformations should prompt suspicion of WT1 mutations. Recent genetic advances enable a more accurate estimation of malignancy risk in these patients, facilitating a conservative nephron-sparing surgery (NSS) approach in select cases, with a focus on preserving residual kidney function and delaying nephrectomies. Other key management strategies include kidney transplantation and addressing DSD and gonadoblastoma. In summary, recent genetic insights underscore the imperative to implement individualized, integrated, and multidisciplinary management strategies for WT1-related disorders. This approach is pivotal in optimizing patient outcomes and addressing the complexities associated with these diverse clinical manifestations.

The Role of Genetic Testing in Adult CKD

Mounting evidence indicates that monogenic disorders are the underlying cause in a significant proportion of patients with CKD. In recent years, the diagnostic yield of genetic testing in these patients has increased significantly as a result of revolutionary developments in genetic sequencing techniques and sequencing data analysis. Identification of disease-causing genetic variant(s) in patients with CKD may facilitate prognostication and personalized management, including nephroprotection and decisions around kidney transplantation, and is crucial for genetic counseling and reproductive family planning. A genetic diagnosis in a patient with CKD allows for screening of at-risk family members, which is also important for determining their eligibility as kidney transplant donors. Despite evidence for clinical utility, increased availability, and data supporting the cost-effectiveness of genetic testing in CKD, especially when applied early in the diagnostic process, many nephrologists do not use genetic testing to its full potential because of multiple perceived barriers. Our aim in this article was to empower nephrologists to (further) implement genetic testing as a diagnostic means in their clinical practice, on the basis of the most recent insights and exemplified by patient vignettes. We stress why genetic testing is of significant clinical benefit to many patients with CKD, provide recommendations for which patients to test and which test(s) to order, give guidance about interpretation of genetic testing results, and highlight the necessity for and essential components of pretest and post-test genetic counseling.

A review of the genetic background in complicated WT1-related disorders

The Wilms tumor 1 (WT1) gene was first identified in 1990 as a strong candidate for conferring a predisposition to Wilms tumor. The WT1 protein has four zinc finger structures (DNA binding domain) at the C-terminus, which bind to transcriptional regulatory sequences on DNA, and acts as a transcription factor. WT1 is expressed during kidney development and regulates differentiation, and is also expressed in glomerular epithelial cells after birth to maintain the structure of podocytes. WT1-related disorders are a group of conditions associated with an aberrant or absent copy of the WT1 gene. This group of conditions encompasses a wide phenotypic spectrum that includes Denys-Drash syndrome (DDS), Frasier syndrome (FS), Wilms-aniridia-genitourinary-mental retardation syndrome, and isolated manifestations of nephropathy or Wilms tumor. The genotype-phenotype correlation is becoming clearer: patients with missense variants in DNA binding sites including C2H2 sites manifest DDS and develop early-onset and rapidly developing end-stage kidney disease. A deeper understanding of the genotype-phenotype correlation has also been obtained in DDS, but no such correlation has been observed in FS. The incidence of Wilms tumor is higher in patients with DDS and exon-truncating variants than in those with non-truncating variants. Here, we briefly describe the genetic background of this highly complicated WT1-related disorders.

Genomic Testing in Patients with Kidney Failure of an Unknown Cause: A National Australian Study

Key Points

Twenty-five percent of those with unexplained kidney failure have a monogenic cause. Whole genome sequencing with broad gene panel analysis is a feasible diagnostic approach in nephrology.

Background

The cause of kidney failure is unknown in approximately 10% of patients with stage 5 chronic kidney disease (CKD). For those who first present to nephrology care with kidney failure, standard investigations of serology, imaging, urinalysis, and kidney biopsy are limited differentiators of etiology. We aimed to determine the diagnostic utility of whole genome sequencing (WGS) with analysis of a broad kidney gene panel in patients with kidney failure of unknown cause.

Methods

We prospectively recruited 100 participants who reached CKD stage 5 at the age of ≤50 years and had an unknown cause of kidney failure after standard investigation. Clinically accredited WGS was performed in this national cohort after genetic counseling. The primary analysis was targeted to 388 kidney-related genes with second-tier, genome-wide, and mitochondrial analysis.

Results

The cohort was 61% male and the average age of participants at stage 5 CKD was 32 years (9 months to 50 years). A genetic diagnosis was made in 25% of participants. Disease-causing variants were identified across autosomal dominant tubulointerstitial kidney disease (6), glomerular disorders (4), ciliopathies (3), tubular disorders (2), Alport syndrome (4), and mitochondrial disease (1). Most diagnoses (80%) were in autosomal dominant, X-linked, or mitochondrial conditions (UMOD ; COL4A5 ; INF2 ; CLCN5 ; TRPC6 ; COL4A4 ; EYA1 ; HNF1B ; WT1 ; NBEA ; m.3243A>G ). Participants with a family history of CKD were more likely to have a positive result (odds ratio, 3.29; 95% confidence interval, 1.10 to 11.29). Thirteen percent of participants without a CKD family history had a positive result. In those who first presented in stage 5 CKD, WGS with broad analysis of a curated kidney disease gene panel was diagnostically more informative than kidney biopsy, with biopsy being inconclusive in 24 of the 25 participants.

Conclusions

In this prospectively ascertained Australian cohort, we identified a genetic diagnosis in 25% of patients with kidney failure of unknown cause.

Evaluation of pathogenicity of WT1 intron variants by in vitro splicing analysis

BACKGROUND

Wilms tumor 1 (WT1; NM_024426) causes Denys-Drash syndrome, Frasier syndrome, or isolated focal segmental glomerulosclerosis. Several WT1 intron variants are pathogenic; however, the pathogenicity of some variants remains undefined. Whether a candidate variant detected in a patient is pathogenic is very important for determining the therapeutic options for the patient.

METHODS

In this study, we evaluated the pathogenicity of WT1 gene intron variants with undetermined pathogenicity by comparing their splicing patterns with those of the wild-type using an in vitro splicing assay using minigenes. The three variants registered as likely disease-causing genes: Mut1 (c.1017-9 T > C(IVS5)), Mut2 (c.1355-28C > T(IVS8)), Mut3 (c.1447 + 1G > C(IVS9)), were included as subjects along the 34 splicing variants registered in the Human Gene Mutation Database (HGMD)®.

RESULTS

The results showed no significant differences in splicing patterns between Mut1 or Mut2 and the wild-type; however, significant differences were observed in Mut3.

CONCLUSION

We concluded that Mut1 and Mut2 do not possess pathogenicity although they were registered as likely pathogenic, whereas Mut3 exhibits pathogenicity. Our results suggest that the pathogenicity of intronic variants detected in patients should be carefully evaluated.

Phenotype, genotype, and clinical outcome of Taiwanese with congenital nephrotic syndrome

BACKGROUND/PURPOSE

Congenital nephrotic syndrome (CNS) is one of the important causes of end-stage kidney disease in children. Studies on the genotype, phenotype, and clinical outcome in infants with CNS caused by genetic mutations are scarce.

METHODS

We analyzed the genetic background, clinical manifestations, treatment response, and prognosis of pediatric patients with CNS in Taiwan.

RESULTS

Fifteen infants with CNS were enrolled, and 11 patients of median age 21 (interquartile range 3∼44) days caused by genetic mutations from 10 unrelated families were included in the study. Of the eleven patients, 9 had extra-renal manifestations including microcephaly, facial dysmorphism, and skeletal anomalies. More than two-thirds of the patients had disease onset before 1 month of age. Diffuse meningeal sclerosis was the most common histological characteristic. Whole exome sequencing followed by direct Sanger sequence revealed mutations in OSGEP (R247Q), WT1 (R366H and R467Q), LAMB2 (Q1209∗ and c. 5432-5451 19 bp deletion), NUP93 (D302V), and LAGE3 (c.188+1G > A). Three of the variants were novel. Corticosteroids and/or immunosuppressants were administered in 2 patients, but both were refractory to treatment. During the mean 3.5 years of follow-up, all but two died of uremia and sepsis. The two survivors reached end-stage kidney disease and required peritoneal dialysis, and one of them underwent uneventful renal transplantation.

CONCLUSION

The majority of patients with CNS in Taiwan were caused by OSGEP followed by WT1 mutation. R247Q is the hotspot mutation of OSGEP in Taiwan. CNS patients in Taiwan suffer from significant morbidity and mortality.

Prophylactic bilateral nephrectomy and preemptive kidney transplantation for Denys-Drash syndrome prior to development of kidney failure

BACKGROUND  : Nephropathy in Denys-Drash syndrome (DDS) develops within a few months of birth, often progressing to kidney failure. Wilms tumors also develop at an early age with a high rate of incidence. When a patient does not have Wilms tumor but develops kidney failure, prophylactic bilateral nephrectomy, and kidney transplantation (KTX) is an optimal approach owing to the high risk of Wilms tumor development. In the case presented here, prophylactic bilateral nephrectomy and KTX were performed in a patient who had not developed Wilms tumor or kidney failure. However, the treatment option is controversial as it involves the removal of a tumor-free kidney and performing KTX in the absence of kidney failure. CASE DIAGNOSIS/TREATMENT: We present the case of a 7-year-old boy, born at 38 weeks gestation. Examinations at the age of 1 year revealed severe proteinuria and abnormal internal and external genitalia. Genetic testing identified a missense mutation in exon 9 of the WT1 gene, leading to the diagnosis of DDS. At the age of 6 years, he had not yet developed Wilms tumor and had grown to a size that allowed him to safely undergo a KTX. His kidney function was slowly deteriorating (chronic kidney disease (CKD) stage 3), but he had not yet developed kidney failure. Two treatment options were considered for this patient: observation until the development of kidney failure or prophylactic bilateral nephrectomy with KTX to avoid Wilms tumor development. After a detailed explanation of options to the patient and family, they decided to proceed with prophylactic bilateral nephrectomy and KTX. At the latest follow-up 4 months after KTX, the patient's kidney functioned well without proteinuria. CONCLUSION: We performed prophylactic bilateral nephrectomy with KTX on a DDS patient who had not developed kidney failure or Wilms tumor by the age of 7 years. Although the risk of development of Wilms tumor in such a patient is unclear, this treatment may be an optimal approach for patients who are physically able to undergo KTX, considering the potentially lethal nature of Wilms tumor in CKD patients.

Hallmark discoveries in the biology of Wilms tumour

The modern study of Wilms tumour was prompted nearly 50 years ago, when Alfred Knudson proposed the 'two-hit' model of tumour development. Since then, the efforts of researchers worldwide have substantially expanded our knowledge of Wilms tumour biology, including major advances in genetics - from cloning the first Wilms tumour gene to high-throughput studies that have revealed the genetic landscape of this tumour. These discoveries improve understanding of the embryonal origin of Wilms tumour, familial occurrences and associated syndromic conditions. Many efforts have been made to find and clinically apply prognostic biomarkers to Wilms tumour, for which outcomes are generally favourable, but treatment of some affected individuals remains challenging. Challenges are also posed by the intratumoural heterogeneity of biomarkers. Furthermore, preclinical models of Wilms tumour, from cell lines to organoid cultures, have evolved. Despite these many achievements, much still remains to be discovered: further molecular understanding of relapse in Wilms tumour and of the multiple origins of bilateral Wilms tumour are two examples of areas under active investigation. International collaboration, especially when large tumour series are required to obtain robust data, will help to answer some of the remaining unresolved questions.

Pediatric Kidney Transplantation: Cancer and Cancer Risk

Children with end-stage kidney disease (ESKD) face a lifetime of complex medical care, alternating between maintenance chronic dialysis and kidney transplantation. Kidney transplantation has emerged as the optimal treatment of ESKD for children and provides important quality of life and survival advantages. Although transplantation is the preferred therapy, lifetime exposure to immunosuppression among children with ESKD is associated with increased morbidity, including an increased risk of cancer. Following pediatric kidney transplantation, cancer events occurring during childhood or young adulthood can be divided into two broad categories: post-transplant lymphoproliferative disorders and non-lymphoproliferative solid tumors. This review provides an overview of cancer incidence, types, outcomes, and preventive strategies in this population.

Developmental Causes of Focal Segmental Glomerulosclerosis

Background

Focal segmental glomerulosclerosis (FSGS) is a histological pattern of glomerular damage that includes idiopathic conditions as well as genetic and non-genetic forms. Among these various etiologies, different phenotypes within the spectrum of congenital anomalies of the kidney and urinary tract (CAKUT) have been associated with FSGS.

Summary

Until recently, the main pathomechanism of how congenital kidney and urinary tract defects lead to FSGS was attributed to a reduced number of nephrons, resulting in biomechanical stress on the remaining glomeruli, detachment of podocytes, and subsequent inability to maintain normal glomerular architecture. The discovery of deleterious single-nucleotide variants in PAX2, a transcription factor crucial in normal kidney development and a known cause of papillorenal syndrome, in individuals with adult-onset FSGS without congenital kidney defects has shed new light on developmental defects that become evident during podocyte injury.

Key Message

In this mini-review, we challenge the assumption that FSGS in CAKUT is caused by glomerular hyperfiltration alone and hypothesize a multifactorial pathogenesis that includes overlapping cellular mechanisms that are activated in both damaged podocytes as well as nephron progenitor cells.

Genetic and epigenetic features of bilateral Wilms tumor predisposition in patients from the Children's Oncology Group AREN18B5-Q

Developing synchronous bilateral Wilms tumor suggests an underlying (epi)genetic predisposition. Here, we evaluate this predisposition in 68 patients using whole exome or genome sequencing (n = 85 tumors from 61 patients with matched germline blood DNA), RNA-seq (n = 99 tumors), and DNA methylation analysis (n = 61 peripheral blood, n = 29 non-diseased kidney, n = 99 tumors). We determine the predominant events for bilateral Wilms tumor predisposition: 1)pre-zygotic germline genetic variants readily detectable in blood DNA [WT1 (14.8%), NYNRIN (6.6%), TRIM28 (5%), and BRCA-related genes (5%)] or 2)post-zygotic epigenetic hypermethylation at 11p15.5 H19/ICR1 that may require analysis of multiple tissue types for diagnosis. Of 99 total tumor specimens, 16 (16.1%) have 11p15.5 normal retention of imprinting, 25 (25.2%) have 11p15.5 copy neutral loss of heterozygosity, and 58 (58.6%) have 11p15.5 H19/ICR1 epigenetic hypermethylation (loss of imprinting). Here, we ascertain the epigenetic and genetic modes of bilateral Wilms tumor predisposition.

Factors predicting the occurrence of disease-causing variants on next-generation sequencing in children with steroid-resistant nephrotic syndrome - implications for resource-constrained settings

BACKGROUND

Enhanced availability of high-throughput sequencing (at progressively reducing costs) has revolutionized the identification of monogenic SRNS. However, in resource-poor settings, it may not be possible to perform next-generation sequencing (NGS) in all children wherein monogenic SRNS is suspected. Besides, the optimal strategy of genetic evaluation (in patients with SRNS) in routine clinical practice in resource-limited settings is unknown.

METHODS

Patients with newly diagnosed SRNS were recruited from our center and followed up prospectively. We analyzed the factor(s) independently predicting the occurrence of disease-causing variants in these patients.

RESULTS

In our study, 36 children/adolescents with SRNS were included (initial steroid resistance in 53%). On targeted NGS, pathogenic/likely pathogenic variants were identified in 31% (n = 11). These included homozygous or compound heterozygous variants in the following genes: ALOX12B, COL4A3, CRB2, NPHS1, NPHS2, PLCE1, and heterozygous variant in WT1 gene. Overall, 14 variants were identified of which 5 (36%) were novel. Age of < 1 or < 2 years and presence of family history of nephrotic syndrome independently predicted the occurrence of monogenic SRNS on multivariate analysis.

CONCLUSIONS

While NGS-based genetic testing in SRNS is increasingly being incorporated in routine clinical practice the world over, the scenario is far from optimal in resource-limited settings. Our study highlights that resources for genetic testing in SRNS should be prioritized for patients with early age at disease onset and presence of family history. Larger studies composed of diverse multi-ethnic cohorts of patients with SRNS are required to further delineate the optimal strategy of genetic evaluation in resource-poor settings. A higher resolution version of the Graphical abstract is available as Supplementary information.

Childhood nephrotic syndrome

Idiopathic nephrotic syndrome is the most common glomerular disease in children. Corticosteroids are the cornerstone of its treatment, and steroid response is the main prognostic factor. Most children respond to a cycle of oral steroids, and are defined as having steroid-sensitive nephrotic syndrome. Among the children who do not respond, defined as having steroid-resistant nephrotic syndrome, most respond to second-line immunosuppression, mainly with calcineurin inhibitors, and children in whom a response is not observed are described as multidrug resistant. The pathophysiology of nephrotic syndrome remains elusive. In cases of immune-mediated origin, dysregulation of immune cells and production of circulating factors that damage the glomerular filtration barrier have been described. Conversely, up to a third of cases of steroid-resistant nephrotic syndrome have a monogenic origin. Multidrug resistant nephrotic syndrome often leads to kidney failure and can cause relapse after kidney transplant. Although steroid-sensitive nephrotic syndrome does not affect renal function, most children with steroid-sensitive nephrotic syndrome have a relapsing course that requires repeated steroid cycles with significant side-effects. To minimise morbidity, some patients require steroid-sparing immunosuppressive agents, including levamisole, mycophenolate mofetil, calcineurin inhibitors, anti-CD20 monoclonal antibodies, and cyclophosphamide. Close monitoring and preventive measures are warranted at onset and during relapse to prevent acute complications (eg, hypovolaemia, acute kidney injury, infections, and thrombosis), whereas long-term management requires minimising treatment-related side-effects. A subset of patients have active disease into adulthood.

Genotype-phenotype correlation of WT1 mutation-related nephropathy in Chinese children

Introduction

This study aimed to analyze the clinical characteristics of nephropathy associated with WT1 gene mutations in Chinese children and explore the relationship between genotype and clinical phenotype.

Methods

Cases diagnosed at the Guangzhou Women and Children's Medical Center, were combined with those retrieved from PubMed and China National Knowledge Infrastructure (CNKI) databases from January 2015 to June 2022 and integrated into a study cohort; grouped according to gene mutation sites, clinical phenotype, and renal pathological types. The clinical characteristics between groups were compared, and the relationship between genotype and age of onset, clinical phenotype, and pathological type were retrospectively analyzed.

Results

The center enrolled 15 confirmed children: seven cases of non-simple nephropathy, including Denys-Drash syndrome (DDS) and Frasier syndrome (FS); eight cases of isolated steroid-resistant nephrotic syndrome (ISRNS); and 13 cases (86.7%) that progressed to end-stage renal disease (ESRD). The initial hemoglobin and bicarbonate levels of patients with clinical non-simple nephropathy were significantly lower than those with simple nephropathy, whereas the serum creatinine levels were higher than those of patients with simple nephropathy. A total of 75 cases of nephropathy associated with WT1 mutations in the study cohort met the inclusion and exclusion criteria. The most common clinical manifestations of WT1 mutations in this cohort were DDS (29/75, 38.7%) and ISRNS (37/75, 49.3%). A renal biopsy was performed in 43 patients, and the common types of renal pathology were focal segmental glomerulosclerosis (23/43, 53.5%) and DMS (13/43, 30.2%). Within the cohort, there were 12 cases (16.0%) in the exon 8 mutation group, 32 (42.6%) in the exon 9 group, 19 (25.3%) in the intron 9 group, and 12 (16.0%) in other gene site mutation groups. Common sites of WT1 mutations in Chinese children were exons 9 and intron 9. Exon 8 mutations were uniquely correlated with the age of onset within three months [5/7; 71.4%; Adjusted standardized residual (AR) = 4.2]. The renal survival time in the exon 8 mutation group was the shortest (P = 0.003).

Discussion

The molecular and biological characteristics of WT1 mutation-related nephropathy determine the clinical type, pathological features, and renal survival time of the disease; and there was a strong correlation between the genotype and clinical phenotype.

A case of Potter sequence with WT1 mutation

Wilms tumor 1 (WT1) is the causative gene of Denys-Drash syndrome and Frasier syndrome, and in most cases, kidney failure develops after birth. We report an unusual case of Potter sequence due to fetal nephropathy and kidney failure with a WT1 mutation. The neonate was born at 37 weeks of gestation, and had no distinctive facial appearance or anomalies of the extremities. The external genitalia were ambiguous. Presence of a penile-like structure or hypertrophic clitoris was noted, and the urethra opened at the base of the penis or clitoris. On ultrasonographic examination, the kidney sizes were small. No kidney cysts were noted, but the kidney parenchymal luminosity was increased. Although the neonate received mechanical ventilation because of severe retractive breathing after birth, he died of poor oxygenation due to air leak syndrome at 60 h after birth. The congenital anomalies of the kidney and urinary tract (CAKUT) gene panel revealed a heterozygous missense mutation in WT1 [NM_024426.6:exon9:c.1400G > A, p.(Arg467Gln)]. In WT1, missense mutations are associated with earlier onset of nephropathy than nonsense or splicing mutations. However, severe cases of fetal onset and early neonatal death with WT1 mutations are rare, and only one severe case with the same missense mutation in WT1 has been reported. Therefore, WT1 mutation may be suspected in Potter sequence patients with external genital abnormalities, and the WT1 missense mutation in our case [NM_024426.6:exon9:c.1400G > A, p.(Arg467Gln)] may indicate a severe case with fetal onset of nephropathy and kidney failure.

Pediatric renal tumor epidemiology: Global perspectives, progress, and challenges

Pediatric renal tumors account for 3%-11% of childhood cancers, the most common of which is Wilms tumor or nephroblastoma. Epidemiology plays a key role in cancer prevention and control by describing the distribution of cancer and discovering risk factors for cancer. Large pediatric research consortium trials have led to a clearer understanding of pediatric renal tumors, identification of risk factors, and development of more risk-adapted therapies. These therapies have improved event-free and overall survival for children. However, several challenges remain and not all children have benefited from the improved outcomes. In this article, we review the global epidemiology of pediatric renal tumors, including key consortium and global studies. We identify current knowledge gaps and challenges facing both high and low middle-incomes countries.

The Genetic and Epigenetic Features of Bilateral Wilms Tumor Predisposition: A Report from the Children's Oncology Group AREN18B5-Q Study

This study comprehensively evaluated the landscape of genetic and epigenetic events that predispose to synchronous bilateral Wilms tumor (BWT). We performed whole exome or whole genome sequencing, total-strand RNA-seq, and DNA methylation analysis using germline and/or tumor samples from 68 patients with BWT from St. Jude Children's Research Hospital and the Children's Oncology Group. We found that 25/61 (41%) of patients evaluated harbored pathogenic or likely pathogenic germline variants, with WT1 (14.8%), NYNRIN (6.6%), TRIM28 (5%) and the BRCA-related genes (5%) BRCA1, BRCA2, and PALB2 being most common. Germline WT1 variants were strongly associated with somatic paternal uniparental disomy encompassing the 11p15.5 and 11p13/WT1 loci and subsequent acquired pathogenic CTNNB1 variants. Somatic coding variants or genome-wide copy number alterations were almost never shared between paired synchronous BWT, suggesting that the acquisition of independent somatic variants leads to tumor formation in the context of germline or early embryonic, post-zygotic initiating events. In contrast, 11p15.5 status (loss of heterozygosity, loss or retention of imprinting) was shared among paired synchronous BWT in all but one case. The predominant molecular events for BWT predisposition include pathogenic germline variants or post-zygotic epigenetic hypermethylation at the 11p15.5 H19/ICR1 locus (loss of imprinting). This study demonstrates that post-zygotic somatic mosaicism for 11p15.5 hypermethylation/loss of imprinting is the single most common initiating molecular event predisposing to BWT. Evidence of somatic mosaicism for 11p15.5 loss of imprinting was detected in leukocytes of a cohort of BWT patients and long-term survivors, but not in unilateral Wilms tumor patients and long-term survivors or controls, further supporting the hypothesis that post-zygotic 11p15.5 alterations occurred in the mesoderm of patients who go on to develop BWT. Due to the preponderance of BWT patients with demonstrable germline or early embryonic tumor predisposition, BWT exhibits a unique biology when compared to unilateral Wilms tumor and therefore warrants continued refinement of its own treatment-relevant biomarkers which in turn may inform directed treatment strategies in the future.

Pediatric renal tumor epidemiology: Global perspectives, progress, and challenges

Pediatric renal tumors account for 3%-11% of childhood cancers, the most common of which is Wilms tumor or nephroblastoma. Epidemiology plays a key role in cancer prevention and control by describing the distribution of cancer and discovering risk factors for cancer. Large pediatric research consortium trials have led to a clearer understanding of pediatric renal tumors, identification of risk factors, and development of more risk-adapted therapies. These therapies have improved event-free and overall survival for children. However, several challenges remain and not all children have benefited from the improved outcomes. In this article, we review the global epidemiology of pediatric renal tumors, including key consortium and global studies. We identify current knowledge gaps and challenges facing both high and low middle-incomes countries.

The pathophysiology of bilateral and multifocal Wilms tumors: What we can learn from the study of predisposition syndromes

Approximately 5% of patients with Wilms tumor present with synchronous bilateral disease. The development of synchronous bilateral Wilms tumor (BWT) is highly suggestive of a genetic or epigenetic predisposition. Patients with known germline predisposition to Wilms tumor (WT1 variants, Beckwith Wiedemann spectrum, TRIM28 variants) have a higher incidence of BWT. This Children's Oncology Group (COG)-International Society for Pediatric Oncology (SIOP-) HARMONICA initiative review for pediatric renal tumors details germline genetic and epigenetic predisposition to BWT development, with an emphasis on alterations in 11p15.5 (ICR1 gain of methylation, paternal uniparental disomy, and postzygotic somatic mosaicism), WT1, TRIM28, and REST. Molecular mechanisms that result in BWT are often also present in multifocal Wilms tumor (multiple separate tumors in one or both kidneys). We identify priority areas for international collaborative research to better understand how predisposing genetic or epigenetic factors associate with response to neoadjuvant chemotherapy, oncologic outcomes, and long-term renal function outcomes.

The Use of Genetics for Reaching a Diagnosis in XY DSD

Reaching a firm diagnosis is vital for the long-term management of a patient with a difference or disorder of sex development (DSD). This is especially the case in XY DSD where the diagnostic yield is particularly low. Molecular genetic technology is playing an increasingly important role in the diagnostic process, and it is highly likely that it will be used more often at an earlier stage in the diagnostic process. In many cases of DSD, the clinical utility of molecular genetics is unequivocally clear, but in many other cases there is a need for careful exploration of the benefit of genetic diagnosis through long-term monitoring of these cases. Furthermore, the incorporation of molecular genetics into the diagnostic process requires a careful appreciation of the strengths and weaknesses of the evolving technology, and the interpretation of the results requires a clear understanding of the wide range of conditions that are associated with DSD.

Alteration in DNA-binding affinity of Wilms tumor 1 protein due to WT1 genetic variants associated with steroid - resistant nephrotic syndrome in children

Approximately one third of children with steroid-resistant nephrotic syndrome (SRNS) carry pathogenic variants in one of the many associated genes. The WT1 gene coding for the WT1 transcription factor is among the most frequently affected genes. Cases from the Czech national SRNS database were sequenced for exons 8 and 9 of the WT1 gene. Eight distinct exonic WT1 variants in nine children were found. Three children presented with isolated SRNS, while the other six manifested with additional features. To analyze the impact of WT1 genetic variants, wild type and mutant WT1 proteins were prepared and the DNA-binding affinity of these proteins to the target EGR1 sequence was measured by microscale thermophoresis. Three WT1 mutants showed significantly decreased DNA-binding affinity (p.Arg439Pro, p.His450Arg and p.Arg463Ter), another three mutants showed significantly increased binding affinity (p.Gln447Pro, p.Asp469Asn and p.His474Arg), and the two remaining mutants (p.Cys433Tyr and p.Arg467Trp) showed no change of DNA-binding affinity. The protein products of WT1 pathogenic variants had variable DNA-binding affinity, and no clear correlation with the clinical symptoms of the patients. Further research is needed to clarify the mechanisms of action of the distinct WT1 mutants; this could potentially lead to individualized treatment of a so far unfavourable disease.

Clinical, Pathological, and Genetic Characteristics in Patients with Focal Segmental Glomerulosclerosis

Background

Approximately 30% of children with steroid-resistant nephrotic syndrome (SRNS) have causative monogenic variants. SRNS represents glomerular disease resulting from various etiologies, which lead to similar patterns of glomerular damage. Patients with SRNS mainly exhibit focal segmental glomerulosclerosis (FSGS). There is limited information regarding associations between histologic variants of FSGS (diagnosed using on the Columbia classification) and monogenic variant detection rates or clinical characteristics. Here, we report FSGS characteristics in a large population of affected patients.

Methods

This retrospective study included 119 patients with FSGS, diagnosed using the Columbia classification; all had been referred to our hospital for genetic testing from 2016 to 2021. We conducted comprehensive gene screening of all patients using a targeted next-generation sequencing panel that included 62 podocyte-related genes. Data regarding patients' clinical characteristics and pathologic findings were obtained from referring clinicians. We analyzed the associations of histologic variants with clinical characteristics, kidney survival, and gene variant detection rates.

Results

The distribution of histologic variants according to the Columbia classification was 45% (n=53) FSGS not otherwise specified, 21% (n=25) cellular, 15% (n=18) perihilar, 13% (n=16) collapsing, and 6% (n=7) tip. The median age at end stage kidney disease onset was 37 years; there were no differences in onset age among variants. We detected monogenic disease-causing variants involving 12 of the screened podocyte-related genes in 34% (40 of 119) of patients. The most common genes were WT1 (23%), INF2 (20%), TRPC6 (20%), and ACTN4 (10%). The perihilar and tip variants had the strongest and weakest associations with detection of monogenic variants (83% and 0%, respectively; P<0.001).

Conclusions

We revealed the distributions of histologic variants of genetic FSGS and nongenetic FSGS in a large patient population. Detailed data concerning gene variants and pathologic findings are important for understanding the etiology of FSGS.

Evaluating Established Roles, Future Perspectives and Methodological Heterogeneity for Wilms’ Tumor 1 (WT1) Antigen Detection in Adult Renal Cell Carcinoma, Using a Novel N-Terminus Targeted Antibody (Clone WT49)

Renal cell carcinoma (RCC) is arguably the deadliest form of genitourinary malignancy and is nowadays viewed as a heterogeneous series of cancers, with the same origin but fundamentally different metabolisms and clinical behaviors. Immunohistochemistry (IHC) is increasingly necessary for RCC subtyping and definitive diagnosis. WT1 is a complex gene involved in carcinogenesis. To address reporting heterogeneity and WT1 IHC standardization, we used a recent N-terminus targeted monoclonal antibody (clone WT49) to evaluate WT1 protein expression in 56 adult RCC (aRCC) cases. This is the largest WT1 IHC investigation focusing exclusively on aRCCs and the first report on clone WT49 staining in aRCCs. We found seven (12.5%) positive cases, all clear cell RCCs, showing exclusively nuclear staining for WT1. We did not disregard cytoplasmic staining in any of the negative cases. Extratumoral fibroblasts, connecting tubules and intratumoral endothelial cells showed the same exclusively nuclear WT1 staining pattern. We reviewed WT1 expression patterns in aRCCs and the possible explanatory underlying metabolomics. For now, WT1 protein expression in aRCCs is insufficiently investigated, with significant discrepancies in the little data reported. Emerging WT1-targeted RCC immunotherapy will require adequate case selection and sustained efforts to standardize the quantification of tumor-associated antigens for aRCC and its many subtypes.

Long-term kidney function in children with Wilms tumour and constitutional WT1 pathogenic variant

BACKGROUND

Wilms tumour (WT) survivors, especially patients with associated syndromes or genitourinary anomalies due to constitutional WT1 pathogenic variant, have increased risk of kidney failure. We describe the long-term kidney function in children with WT and WT1 pathogenic variant to inform the surgical strategy and oncological management of such complex children.

METHODS

Retrospective analysis of patients with WT and constitutional WT1 pathogenic variant treated at a single centre between 1993 and 2016, reviewing genotype, phenotype, tumour histology, laterality, treatment, patient survival, and kidney outcome.

RESULTS

We identified 25 patients (60% male, median age at diagnosis 14 months, range 4-74 months) with WT1 deletion (4), missense (2), nonsense (8), frameshift (7), or splice site (4) pathogenic variant. Thirteen (52%) had bilateral disease, 3 (12%) had WT-aniridia, 1 had incomplete Denys-Drash syndrome, 11 (44%) had genitourinary malformation, and 10 (40%) had no phenotypic anomalies. Patient survival was 100% and 3 patients were in remission after relapse at median follow-up of 9 years. Seven patients (28%) commenced chronic dialysis of which 3 were after bilateral nephrectomies. The overall kidney survival for this cohort as mean time to start of dialysis was 13.38 years (95% CI: 10.3-16.4), where 7 patients experienced kidney failure at a median of 5.6 years. All of these 7 patients were subsequently transplanted. In addition, 2 patients have stage III and stage IV chronic kidney disease and 12 patients have albuminuria and/or treatment with ACE inhibitors. Four patients (3 frameshift; 1 WT1 deletion) had normal blood pressure and kidney function without proteinuria at follow-up from 1.5 to 12 years.

CONCLUSIONS

Despite the known high risk of kidney disease in patients with WT and constitutional WT1 pathogenic variant, nearly two-thirds of patients had sustained native kidney function, suggesting that nephron-sparing surgery (NSS) should be attempted when possible without compromising oncological risk. Larger international studies are needed for accurate assessment of WT1genotype-kidney function phenotype correlation.

Case Report: A Pathogenic Missense Variant of WT1 Cosegregates With Proteinuria in a Six-Generation Chinese Family With IgA Nephropathy

Immunoglobulin A (IgA) nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide. In addition to hematuria, proteinuria is observed in a considerable proportion of patients with IgAN and has proven to be a strong risk factor for disease progression. Although the exact pathogenesis of IgAN is still unclear, genetic factors are widely considered to play a role in its occurrence and development. Here, we investigated a large IgAN-associated pedigree of 47 members belonging to six generations. Two members of the family who presented with proteinuria and hematuria were diagnosed with IgAN through renal biopsy. Four other members also exhibited proteinuria or hematuria but without renal biopsy. Using whole-exome sequencing, we identified a likely pathogenic variant in WT1 (c.1397C>T; p.Ser466Phe) that cosegregated with proteinuria in the affected family members. In addition, another pathogenic variant in NPHS1 (c.3478C>T; p.Arg1160Ter) was identified; however, it did not cosegregate with abnormal proteinuria. Compared to individuals in the pedigree with only one heterozygous WT1 variant (c.1397C>T; p.Ser466Phe), the proband and her younger brother carried an additional WT1 variant (c.1433-10G>A) and presented with a more severe phenotype and rapid progression to end-stage kidney disease. Our findings suggest the WT1 missense variant (c.1397C>T; p.Ser466Phe)-induced primary podocyte injury might contribute to the proteinuria phenotype and IgAN progression in this pedigree.

WT1 complete gonadal dysgenesis with membranoproliferative glomerulonephritis: case series and literature review

BACKGROUND

Intronic WT1 mutations are usually causative of Frasier syndrome with focal segmental glomerulosclerosis as the characteristic nephropathy. Membranoproliferative glomerulonephritis is not commonly associated with disorders of sex development but has been recently identified as a WT1-associated nephropathy, but usually in cases of exonic mutations in either isolated Wilms tumor or Denys-Drash syndrome.

METHODS

The clinical and genetic data from 3 individuals are reported.

RESULTS

This report describes the kidney manifestations in 3 individuals from 2 unrelated families with Frasier syndrome intronic WT1 mutations, noting that 2 of the 3 individuals have histologically confirmed membranoproliferative glomerulonephritis.

CONCLUSIONS

These case reports support expansion of the clinical spectrum of the kidney phenotypes associated with Frasier syndrome providing evidence of an association between WT1 mutation and an immune complex-related membranoproliferative glomerulonephritis. A higher resolution version of the Graphical abstract is available as Supplementary information.

Spectrum of Clinical Manifestations in Children With WT1 Mutation: Case Series and Literature Review

BACKGROUND

Mutations of the Wilms tumor suppressor-1 gene (WT1) are associated with life-threatening glomerulopathy, disorders of sexual development, Wilm's tumor, and gonadal malignancies. Our objectives were to describe the clinical presentations, age of progression, and onset of complications of WT1 mutation through a case series and literature review.

METHODS

A retrospective study included all patients followed at the University of Miami/Holtz Children's Hospital from January 2000 to December 2020 with a diagnosis of WT1 mutation. A literature review of WT1 mutation cases was analyzed for clinical manifestations, karyotype, and long-term outcomes.

RESULTS

The WT1 mutation was identified in 9 children, median age at presentation of 0.9 years (range 1 week to 7 years). A total of four had female phenotypes, and 5 had abnormalities of male external genitalia, while all had XY karyotypes. All progressed to end-stage kidney disease (ESKD) and received a kidney transplant at a median age of 5 years (1.5-15 years). During a median time of follow-up of 9 years (range 2-28 years), there were 2 allograft losses after 7 and 10 years and no evidence of post-transplant malignancy. From 333 cases identified from the literature review, the majority had female phenotype 66% (219/333), but the predominant karyotype was XY (55%, 183/333). Of the female phenotypes, 32% (69/219) had XY sex reversal. Wilm's tumor occurred in 24%, predominantly in males with gonadal anomalies.

CONCLUSIONS

Early recognition of WT1 mutation is essential for comprehensive surveillance of potential malignancy, avoidance of immunosuppressants for glomerulopathy, and establishing long-term multidisciplinary management.

Management of Steroid-Resistant Nephrotic Syndrome in Children

Nephrotic syndrome (NS) affects 115-169 children per 100,000, with rates varying by ethnicity and location. Immune dysregulation, systemic circulating substances, or hereditary structural abnormalities of the podocyte are considered to have a role in the etiology of idiopathic NS. Following daily therapy with corticosteroids, more than 85% of children and adolescents (often aged 1 to 12 years) with idiopathic nephrotic syndrome have full proteinuria remission. Patients with steroid-resistant nephrotic syndrome (SRNS) do not demonstrate remission after four weeks of daily prednisolone therapy. The incidence of steroid-resistant nephrotic syndrome in children varies between 35 and 92 percent. A third of SRNS patients have mutations in one of the important podocyte genes. An unidentified circulating factor is most likely to blame for the remaining instances of SRNS.

The aim of this article is to explore and review the genetic factors and management of steroid-resistant nephrotic syndrome. An all language literature search was conducted on MEDLINE, COCHRANE, EMBASE, and Google Scholar till September 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: “Steroid resistance”, “nephrotic syndrome”, “nephrosis” and “hypoalbuminemia”. We comprehensively reviewed the literature on the epidemiology, genetics, current treatment protocols, and management of steroid-resistant nephrotic syndrome.

We found that for individuals with non-genetic SRNS, calcineurin inhibitors (cyclosporine and tacrolimus) constitute the current mainstay of treatment, with around 70% of patients achieving full or partial remission and an acceptable long-term prognosis. Patients with SRNS who do not react to calcineurin inhibitors or other immunosuppressive medications may have deterioration in kidney function and may develop end-stage renal failure. Nonspecific renal protective medicines, such as angiotensin-converting enzyme inhibitors, angiotensin 2 receptor blockers, and anti-lipid medications, slow the course of the illness. Recurrent focal segmental glomerulosclerosis in the allograft affects around a third of individuals who get a kidney transplant, and it frequently responds to a combination of plasma exchange, rituximab, and increased immunosuppression. Despite the fact that these results show a considerable improvement in outcome, further multicenter controlled studies are required to determine the optimum drugs and regimens to be used.

Society for Endocrinology UK Guidance on the initial evaluation of a suspected difference or disorder of sex development (Revised 2021)

It is paramount that any child or adolescent with a suspected difference or disorder of sex development (DSD) is assessed by an experienced clinician with adequate knowledge about the range of conditions associated with DSD and is discussed with the regional DSD service. In most cases, the paediatric endocrinologist within this service acts as the first point of contact but involvement of the regional multidisciplinary service will also ensure prompt access to specialist psychology and nursing care. The underlying pathophysiology of DSD and the process of delineating this should be discussed with the parents and affected young person with all diagnostic tests undertaken in a timely fashion. Finally, for rare conditions such as these, it is imperative that clinical experience is shared through national and international clinical and research collaborations.

Tubuloglomerular Disease With Cone-Shaped Epiphyses Associated With Hypomorphic Variant and a Novel p.Cys14Arg in the TTC21B Gene: A Case Report

Monogenic nephrotic syndrome (NS) is associated with a resistance to initial glucocorticoid therapy and causative variants, which may be found in several genes influencing podocyte stability and kidney development. The TTC21B gene, which encodes the retrograde intraflagellar transport protein IFT139, is found mostly in association with ciliopathies in humans. The role of this protein in podocyte cytoskeleton stability was confirmed later and the mutated TTC21B also may be associated with proteinuric diseases, such as nephrotic syndrome. Our patient manifested as an infant with brachydactyly, nephrotic-range proteinuria, and renal tubular acidosis, and a kidney biopsy revealed focal segmental glomerulosclerosis (FSGS). Multiple phalangeal cone-shaped epiphyses of the hand were seen on X-ray. Next-generation sequencing revealed the well-described p.Pro209Leu heterozygous variant and a novel heterozygous p.Cys14Arg variant in the TTC21B gene. Our finding confirmed that the causative variants in the TTC21B gene may contribute to a spectrum of clinical features, such as glomerular proteinuric disease with tubulointerstitial involvement and skeletal abnormalities.

Anesthetic and surgical considerations for staged bilateral nephrectomies in a pediatric patient: A case report

We present a 9-year-old patient with end-stage renal disease, on peritoneal dialysis, who underwent a staged prone retroperitoneoscopic bilateral nephrectomy. Bilateral nephrectomy was indicated in preparation for renal transplant in the context of genetic predisposition malignancy when immunosuppressed. The two mirror-image surgeries enable the comparison of the anesthetic management and outcomes in a single patient. Features of interest to anesthesiologists include approach to a child with chronic kidney disease, different requirements for intraoperative antihypertensives; pain management strategies, including a comparison of erector spinae plane block with and without adjunct dexmedetomidine; anesthetic management of retroperitoneoscopic pediatric surgery and the first description of using a Foley bag attached to a peritoneal dialysis catheter to aid in diagnosis and repair of posterior peritoneal cavity entry.

Suspicion of Frasier's Syndrome in the Nephrology Unit of the State University Hospital of Haiti: Case Study and Review of Literature

Objective

Frasier syndrome is a rare genetic nephropathy characterized by the presence of progressive glomerulopathy with proteinuria associated with male pseudo hermaphroditism. This case study described a picture of a young boy where the clinical suspicion context reminded the Frasier syndrome. To our knowledge, this case is the first described in Haiti.

Case Study

This is a 19-year-old young phenotypically male, born with a genital anomaly, was seen on referral at the nephrology/dialysis unit of the internal medicine department of the State University Hospital of Haiti for evaluation and follow-up. Insidious progression of symptoms had occurred over 3 years. Over three months of outpatient follow-up, he had four sets of renal labs drawn, and all showed impaired renal function. At the ultrasound, a bilateral cryptorchidism is described in the inguinal, and presence of functional ovaries with follicles of variable size scattered in the parenchyma. So, in the light of these anamnestic, clinical and paraclinical findings, we concluded to the diagnosis of end-stage renal failure by progressive glomerulopathy in a context of Frasier's syndrome.

Conclusion

With any clinical picture consisting of genital anomalies at birth, renal symptomatology during childhood and the diagnosis of renal failure during adolescence, rare genetic nephropathies, such as Frasier syndrome must be considered.

WT1 Pathogenic Variants are Associated with a Broad Spectrum of Differences in Sex Development Phenotypes and Heterogeneous Progression of Renal Disease

Wilms' tumor suppressor gene 1 (WT1) plays an essential role in urogenital and kidney development. Heterozygous germline pathogenic allelic variants of WT1 have been classically associated with Denys-Drash syndrome (DDS) and Frasier syndrome (FS). Usually, exonic pathogenic missense variants in the zinc finger region are the cause of DDS, whereas pathogenic variants affecting the canonic donor lysine-threonine-serine splice site in intron 9 cause FS. Phenotypic overlap between WT1 disorders has been frequently observed. New WT1 variant-associated phenotypes, such as 46,XX testicular/ovarian-testicular disorders of sex development (DSD) and primary ovarian insufficiency, have been reported. In this report, we describe the phenotypes and genotypes of 7 Brazilian patients with pathogenic WT1 variants. The molecular study involved Sanger sequencing and massively parallel targeted sequencing using a DSD-associated gene panel. Six patients (5 with a 46,XY karyotype and 1 with a 46,XX karyotype) were initially evaluated for atypical genitalia, and a 46,XY patient with normal female genitalia sought medical attention for primary amenorrhea. Germ cell tumors were identified in 2 patients, both with variants affecting alternative splicing of WT1 between exons 9 and 10. Two pathogenic missense WT1 variants were identified in two 46,XY individuals with Wilms' tumors; both patients were <1 year of age at the time of diagnosis. A novel WT1 variant, c.1453_1456 (p.Arg485Glyfs*14), was identified in a 46,XX patient with testicular DSD. Nephrotic proteinuria was diagnosed in all patients, including 3 who underwent renal transplantation after progressing to end-stage kidney disease. The expanding phenotypic spectrum associated with WT1 variants in XY and XX individuals confirms their pivotal role in gonadal and renal development as well as in tumorigenesis, emphasizing the clinical implications of these variants in genetic diagnosis.

Wilms tumour surveillance in at-risk children: Literature review and recommendations from the SIOP-Europe Host Genome Working Group and SIOP Renal Tumour Study Group

Since previous consensus-based Wilms tumour (WT) surveillance guidelines were published, novel genes and syndromes associated with WT risk have been identified, and diagnostic molecular tests for previously known syndromes have improved. In view of this, the International Society of Pediatric Oncology (SIOP)-Europe Host Genome Working Group and SIOP Renal Tumour Study Group hereby present updated WT surveillance guidelines after an extensive literature review and international consensus meetings. These guidelines are for use by clinical geneticists, pediatricians, pediatric oncologists and radiologists involved in the care of children at risk of WT. Additionally, we emphasise the need to register all patients with a cancer predisposition syndrome in national or international databases, to enable the development of better tumour risk estimates and tumour surveillance programs in the future.

Genetic testing in the diagnosis of chronic kidney disease: recommendations for clinical practice

The overall diagnostic yield of massively parallel sequencing–based tests in patients with chronic kidney disease (CKD) is 30% for paediatric cases and 6–30% for adult cases. These figures should encourage nephrologists to frequently use genetic testing as a diagnostic means for their patients. However, in reality, several barriers appear to hinder the implementation of massively parallel sequencing–based diagnostics in routine clinical practice. In this article we aim to support the nephrologist to overcome these barriers. After a detailed discussion of the general items that are important to genetic testing in nephrology, namely genetic testing modalities and their indications, clinical information needed for high-quality interpretation of genetic tests, the clinical benefit of genetic testing and genetic counselling, we describe each of these items more specifically for the different groups of genetic kidney diseases and for CKD of unknown origin.

Genotype-Phenotype Correlation in WT1 Exon 8 to 9 Missense Variants

Introduction

WT1 missense mutation in exon 8 or 9 causes infantile nephrotic syndrome with early progression to end-stage kidney disease (ESKD), Wilms tumor, and 46,XY female. However, some patients with missense mutations in exon 8 or 9 progress to ESKD in their teens or later. Therefore, we conducted a systematic review and functional analysis of WT1 transcriptional activity.

Methods

We conducted a systematic review of 174 cases with WT1 exon 8 or 9 missense variants from our cohort (n=13) and previous reports (n=161). Of these cases, mild and severe genotypes were selected for further in vitro functional analysis using luciferase assay.

Results

The median age of developing ESKD was 1.17 years. A comparative study was conducted among three WT1 genotype classes: mutations of the DNA-binding site (DBS group), mutations outside the DNA-binding site but at sites important for zinc finger structure formation by 2 cysteines and 2 histidines (C2H2 group), and mutations leading to other amino acid changes (Others group). The DBS group showed the severest phenotype and the C2H2 group was intermediate, whereas the Others group showed the mildest phenotype (developing ESKD at 0.90, 2.00, and 3.92 years, respectively, with significant differences). In vitro functional analysis showed dominant-negative effects for all variants; in addition, the DBS and C2H2 mutations were associated with significantly lower WT1 transcriptional activity than the other mutations.

Conclusion

Not only the DNA-binding site but also C2H2 zinc finger structure sites are important for maintaining WT1 transcriptional activity, and their mutation causes severe clinical symptoms.

Management of congenital nephrotic syndrome: consensus recommendations of the ERKNet-ESPN Working Group

Congenital nephrotic syndrome (CNS) is a heterogeneous group of disorders characterized by nephrotic-range proteinuria, hypoalbuminaemia and oedema, which manifest in utero or during the first 3 months of life. The main cause of CNS is genetic defects in podocytes; however, it can also be caused, in rare cases, by congenital infections or maternal allo-immune disease. Management of CNS is very challenging because patients are prone to severe complications, such as haemodynamic compromise, infections, thromboses, impaired growth and kidney failure. In this consensus statement, experts from the European Reference Network for Kidney Diseases (ERKNet) and the European Society for Paediatric Nephrology (ESPN) summarize the current evidence and present recommendations for the management of CNS, including the use of renin-angiotensin system inhibitors, diuretics, anticoagulation and infection prophylaxis. Therapeutic management should be adapted to the clinical severity of the condition with the aim of maintaining intravascular euvolaemia and adequate nutrition, while preventing complications and preserving central and peripheral vessels. We do not recommend performing routine early nephrectomies but suggest that they are considered in patients with severe complications despite optimal conservative treatment, and before transplantation in patients with persisting nephrotic syndrome and/or a WT1-dominant pathogenic variant.

Genetic Disorders of the Glomerular Filtration Barrier

The glomerular filtration barrier is a highly specialized capillary wall comprising fenestrated endothelial cells, podocytes, and an intervening basement membrane. In glomerular disease, this barrier loses functional integrity, allowing the passage of macromolecules and cells, and there are associated changes in both cell morphology and the extracellular matrix. Over the past 3 decades, there has been a transformation in our understanding about glomerular disease, fueled by genetic discovery, and this is leading to exciting advances in our knowledge about glomerular biology and pathophysiology. In current clinical practice, a genetic diagnosis already has important implications for management, ranging from estimating the risk of disease recurrence post-transplant to the life-changing advances in the treatment of atypical hemolytic uremic syndrome. Improving our understanding about the mechanistic basis of glomerular disease is required for more effective and personalized therapy options. In this review, we describe genotype and phenotype correlations for genetic disorders of the glomerular filtration barrier, with a particular emphasis on how these gene defects cluster by both their ontology and patterns of glomerular pathology.

Genetic screening in children with challenging nephrotic syndrome

Genetic screening paradigms for the nephrotic syndrome (NS) in the developed world are well established; however, screening in developing countries has received only minor attention. We retrospectively analyzed a cohort of all children who underwent genetic testing for challenging NS from our registry in the 10-year interval from 2000 to 2010 and based on 58 patients aged 0-12 years with at least one of the following clinical diagnosis: Nonsyndromic steroid-resistant nephrotic syndrome (SRNS), familial NS, and congenital NS. Of these, 23 patients (~40%) had a history of familial disease occurrence. All cases were screened for NPHS2 and WT1 mutations by direct sequencing of all exons of the genes. In addition, all patients who were diagnosed during the first three months of life were screened for NPHS1 mutations too. A genetic disease cause was identified in 12 patients (20.7%); of these, five novel mutations, all in NPHS2 accounting for 42% of all mutations and 9% of the cohort. Nine patients were found to have NPHS2 mutations. Only one case with SRNS had a mutation in WT1. Of the five congenital NS, two cases were found to have NPHS1 mutations and one case with NPHS2 mutation. Therefore, mutations in NPHS2 were the most commonly identified and explained in 15.5% of the screened patients and WT1 mutation in 1.7% of cases, whereas NPHS1 mutations were found in 40% of congenital NS cases. A genetic disease cause was identified in 20.7% of the screened patients. Among 12 identified mutations, abnormalities in NPHS2 (n = 9) were most commonly identified.

A no-nonsense approach to hereditary kidney disease

The advent of a new class of aminoglycosides with increased translational readthrough of nonsense mutations and reduced toxicity offers a new therapeutic strategy for a subset of patients with hereditary kidney disease. The renal uptake and retention of aminoglycosides at a high intracellular concentration makes the kidney an ideal target for this approach. In this review, we explore the potential of aminoglycoside readthrough therapy in a number of hereditary kidney diseases and discuss the therapeutic window of opportunity for subclasses of each disease, when caused by nonsense mutations.