Genetic aspects of congenital nephrotic syndrome: a consensus statement from the ERKNet-ESPN inherited glomerulopathy working group

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.

Rare heterozygous variants in paediatric steroid resistant nephrotic syndrome - a population-based analysis of their significance

Genetic testing in nephrotic syndrome may identify heterozygous predicted-pathogenic variants (HPPVs) in autosomal recessive (AR) genes that are known to cause disease in the homozygous or compound heterozygous state. In such cases, it can be difficult to define the variant's true significance and questions remain about whether a second pathogenic variant has been missed during analysis or whether the variant is an incidental finding. There are now known to be over 70 genes associated with nephrotic syndrome, the majority inherited as an AR trait. Knowledge of whether such HPPVs occur with equal frequency in patients compared to the general population would assist interpretation of their significance. Exome sequencing was performed on 187 Steroid-Resistant Nephrotic Syndrome (SRNS) paediatric patients recruited to a UK rare disease registry plus originating from clinics at Evelina, London. 59 AR podocytopathy linked genes were analysed in each patient and a list of HPPVs created. We compared the frequency of detected HPPVs with a 'control' population from the gnomAD database containing exome data from approximately 50,000 individuals. A bespoke filtering process was used for both patients and controls to predict 'likely pathogenicity' of variants. In total 130 Caucasian SRNS patients were screened across 59 AR genes and 201 rare heterozygous variants were identified. 17/201 (8.5%) were assigned as 'likely pathogenic' (HPPV) using our bespoke filtering method. Comparing each gene in turn, for SRNS patients with a confirmed genetic diagnosis, in 57 of the 59 genes we found no statistically significant difference in the frequency of these HPPVs between patients and controls (In genes ARHGDIA and TP53RK, we identified a significantly higher number of HPPVs in the control population compared with the patients when filtering was performed with 'high stringency' settings only). In the SRNS patients without a genetics diagnosis confirmed, there was no statistically significant difference identified in any gene between patient and control. In children with SRNS, we propose that identification of HPPV in AR podocytopathy linked genes is not necessarily representative of pathogenicity, given that the frequency is similar to that seen in controls for the majority. Whilst this may not exclude the presence of genetic kidney disease, this type of heterozygous variant is unlikely to be causal and each result must be interpreted in its clinical context.

Managing venous thrombosis in a pediatric patient with short bowel and congenital nephrotic syndromes: a case report emphasizing rivaroxaban level monitoring

Direct Oral Anticoagulants (DOACs) typically exhibit a predictable pharmacokinetic and pharmacodynamic response at a fixed dose, not necessitating monitoring under standard conditions. Yet, in specific clinical scenarios that can impair it, like Congenital Nephrotic Syndrome (CNS) or Short Bowel Syndrome (SBS) due to absorption issues, anti-thrombin III (AT-III) deficiency and non-selective proteinuria, adjusting the dosage to achieve appropriate plasma concentrations could prove beneficial. We report a 3-month-old female with catheter-related jugular thrombosis affected by CNS concomitant to SBS and failure of both treatments with heparin and warfarin, that was switched to dose-adjusted pediatric rivaroxaban. Rivaroxaban was adjusted to reach peak levels between 189 and 419 ng/ml and the lower trough levels between 6 and 87 ng/ml. Increasing doses were needed due to SBS related malabsorption but a complete permeabilization of the vein was achieved without bleeding complications. The use of anti-Xa adjusted rivaroxaban could be an alternative to improve anticoagulation and secondary thromboprophylaxis in pediatric patients SBS and an option to children with CNS.

Native nephrectomy in advanced pediatric kidney disease: indications, timing, and surgical approaches

In pediatric kidney failure, native kidneys may pose a risk to successful transplant outcomes. The indications and timing of native nephrectomy represent a controversial management decision. A lack of high-quality, outcomes-based data has prevented development of evidence-based guidelines for intervention. In this article, we review the published literature on medical indications for native nephrectomy and current knowledge gaps. In addition, we provide a surgical perspective regarding timing and approach.

A Case of Congenital Nephrotic Syndrome with Crescents Caused by a Novel Compound Heterozygous Pairing of NPHS1 Genetic Variants

Congenital nephrotic syndrome is an autosomal recessive inherited disorder that manifests as steroid-resistant massive proteinuria in the first three months of life. Defects in the glomerular filtration mechanism are the primary etiology. We present a child who developed severe nephrotic syndrome at two weeks of age and eventually required a bilateral nephrectomy. Genetic testing revealed compound heterozygous variants in NPHS1 including a known pathogenic variant and a missense variant of uncertain significance. Light microscopy revealed crescent formation-an atypical finding in congenital nephrotic syndrome caused by nephrin variants-in addition to focal segmental and global glomerulosclerosis. Electron microscopy showed diffuse podocyte foot process effacement. Confocal and Airyscan immunofluorescence microcopy showed aggregation of nephrin in the podocyte cell body that is not a result of diffuse podocyte foot process effacement as seen in minimal change disease. These findings confirm the novel variant as pathogenic.

Quercetin-targeted AKT1 regulates the Raf/MEK/ERK signaling pathway to protect against doxorubicin-induced nephropathy in mice

BACKGROUND

Doxorubicin is an anthracycline antitumor agent commonly used in clinical practice, which has some nephrotoxicity and is often used to establish mouse models of kidney injury for basic medical research. This study will investigate the protective effect of quercetin on renal function in doxorubicin-induced nephropathy mice.

METHODS

C57BL/6 mice were divided into control, model, and quercetin low-, and high-dose groups. Serum and urine were collected to analyze markers of kidney function. H&E staining was used to detect pathological changes in renal tissues. Transmission electron microscopy was performed to observe the ultrastructural changes in renal tissues. Immunohistochemistry was performed to detect the changes of Ang II. RT-qPCR was performed to detect the changes of cytokines. ELISA was used to detect changes in serum inflammatory factors. Molecular docking was performed to verify the targeting relationship between quercetin and AKT1. Western blot was performed to detect Bax, Bcl-2, Cyt-c, AKT1, Raf, MEK, and ERK proteins.

RESULTS

Quercetin could induce the recovery of kidney function in kidney-injured mice; H&E results showed that kidney tissue damage and tissue fibrosis were reduced in kidney-injured mice under quercetin. The mitochondrial swollen structure was destroyed by doxorubicin, while the mitochondrial structure was restored under quercetin. The levels of abnormal apoptotic proteins Bax and Bcl-2 were regulated to normal by quercetin. The high expression of Ang II caused by doxorubicin was down-regulated by quercetin. Abnormal inflammatory factors caused by doxorubicin were reversed by quercetin. Western blot experiments showed that quercetin regulated the protein levels of AKT1 and Raf/MEK/ERK and inhibited the detrimental effects of doxorubicin.

CONCLUSION

Quercetin may mitigate doxorubicin-induced kidney injury in mice by regulating renal cell inflammatory factors and Raf/MEK/ERK signaling pathway through AKT1 to promote recovery of renal function.

Genetic nephrotic syndrome associated with disturbed function of glomerular slit membrane and podocyte cytoskeleton in children

BACKGROUND

Genetic nephrotic syndrome is caused by pathogenic variants in genes encoding proteins necessary for the stability and functionality of the glomerular filtration barrier. To date, more than 70 genes associated with steroid-resistant nephrotic syndrome have been identified. We review the clinical and molecular aspects of genetic nephrotic syndrome with a particular focus on genes associated with slit membrane and podocyte cytoskeleton defects. Sanger sequencing and next-generation sequencing are widely used in the identification of novel gene variants and help us gain a better understanding of the disease. Despite these findings, therapy is mainly supportive and focused on the reduction of proteinuria and management of chronic kidney disease with an unfavorable outcome for a significant proportion of cases. Positive therapeutic effects of immunosuppressive drugs have been reported in some patients; however, their long-time administration cannot be generally recommended.

CONCLUSION

Personalized treatment based on understanding the distinct disease pathogenesis is needed. With this, it will be possible to avoid harmful immunosuppressive therapy and improve outcomes and quality of life for pediatric patients suffering from genetic nephrotic syndrome.

Exome Sequencing Revealed a Novel Splice Site Variant in the CRB2 Gene Underlying Nephrotic Syndrome

Background and Objectives: Nephrotic syndrome (NS) is a kidney disease where the patient has a classic triad of signs and symptoms including hypercholesterolemia, hypoalbuminemia, proteinuria (>3.5 g/24 h), and peripheral edema. In case of NS, the damaged nephrons (structural and functional unit of the kidney) filter unwanted blood contents to make urine. Thus, the urine contains unwanted proteins (proteinuria) and blood cells (hematuria), while the bloodstream lacks enough protein albumin (hypoalbuminemia). Nephrotic syndrome is divided into two types, primary NS, and secondary NS. Primary NS, also known as primary glomerulonephrosis, is the result of a glomerular disease that is limited to the kidney, while secondary NS is a condition that affects the kidney and other parts of the body. The main causes of primary NS are minimal change disease, membranous glomerulonephritis, and focal segmental glomerulosclerosis. In the present study we recruited a family segregating primary NS with the aim to identify the underlying genetic etiology. Such type of study is important in children because it allows counseling of other family members who may be at risk of developing NS, predicts risk of recurrent disease phenotypes after kidney transplant, and predicts response to immunosuppressive therapy. Materials and Methods: All affected individuals were clinically evaluated. Clinical examination, results of laboratory tests, and biopsy investigations led us to the diagnosis. The next-generation sequencing technique (whole-exome sequencing) followed by Sanger sequencing identified a novel homozygous splice site variant (NM_173689.7: c.941-3C>T) in the CRB2 gene. The variant was present in a homozygous state in the affected individuals, while in a heterozygous state in phenotypically normal parents. Results: The study expanded the spectrum of the mutations in the gene CRB2 responsible for causing NS. Conclusions: In addition, the study will also help in genetic counseling, carrier testing, and prenatal and/or postnatal early diagnosis of the disease in the affected family.

Conservation and Diversification of tRNA t6A-Modifying Enzymes across the Three Domains of Life

The universal N⁶-threonylcarbamoyladenosine (t⁶A) modification occurs at position 37 of tRNAs that decipher codons starting with adenosine. Mechanistically, t⁶A stabilizes structural configurations of the anticodon stem loop, promotes anticodon–codon pairing and safeguards the translational fidelity. The biosynthesis of tRNA t⁶A is co-catalyzed by two universally conserved protein families of TsaC/Sua5 (COG0009) and TsaD/Kae1/Qri7 (COG0533). Enzymatically, TsaC/Sua5 protein utilizes the substrates of L-threonine, HCO₃⁻/CO₂ and ATP to synthesize an intermediate L-threonylcarbamoyladenylate, of which the threonylcarbamoyl-moiety is subsequently transferred onto the A37 of substrate tRNAs by the TsaD–TsaB –TsaE complex in bacteria or by the KEOPS complex in archaea and eukaryotic cytoplasm, whereas Qri7/OSGEPL1 protein functions on its own in mitochondria. Depletion of tRNA t⁶A interferes with protein homeostasis and gravely affects the life of unicellular organisms and the fitness of higher eukaryotes. Pathogenic mutations of YRDC, OSGEPL1 and KEOPS are implicated in a number of human mitochondrial and neurological diseases, including autosomal recessive Galloway–Mowat syndrome. The molecular mechanisms underscoring both the biosynthesis and cellular roles of tRNA t⁶A are presently not well elucidated. This review summarizes current mechanistic understandings of the catalysis, regulation and disease implications of tRNA t⁶A-biosynthetic machineries of three kingdoms of life, with a special focus on delineating the structure–function relationship from perspectives of conservation and diversity.

The IRE1α pathway in glomerular diseases: The unfolded protein response and beyond

Endoplasmic reticulum (ER) function is vital for protein homeostasis ("proteostasis"). Protein misfolding in the ER of podocytes (glomerular visceral epithelial cells) is an important contributor to the pathogenesis of human glomerular diseases. ER protein misfolding causes ER stress and activates a compensatory signaling network called the unfolded protein response (UPR). Disruption of the UPR, in particular deletion of the UPR transducer, inositol-requiring enzyme 1α (IRE1α) in mouse podocytes leads to podocyte injury and albuminuria in aging, and exacerbates injury in glomerulonephritis. The UPR may interact in a coordinated manner with autophagy to relieve protein misfolding and its consequences. Recent studies have identified novel downstream targets of IRE1α, which provide new mechanistic insights into proteostatic pathways. Novel pathways of IRE1α signaling involve reticulophagy, mitochondria, metabolism, vesicular trafficking, microRNAs, and others. Mechanism-based therapies for glomerulopathies are limited, and development of non-invasive ER stress biomarkers, as well as targeting ER stress with pharmacological compounds may represent a therapeutic opportunity for preventing or attenuating progression of chronic kidney disease.

Assessment of hearing levels in children with nephrotic syndrome

OBJECTIVE

Due to the similarities in the physiological mechanisms and antigenicity of the kidney and cochlea, they are simultaneously affected by certain diseases and drugs. Therefore, the purpose of this study was to investigate whether the hearing functions of patients with nephrotic syndrome (NS) were affected by the severity of the disease and the cyclosporine treatment.

METHODS

The sample of this study consisted of 87 participants, including 65 patients (130 ears) with NS and 22 age- and sex-matched normal hearing children (44 ears). Based on the severity of the disease, the patients were divided into two groups: infrequently relapsing nephrotic syndrome (IRNS) and steroid-dependent or frequently relapsing nephrotic syndrome (SD/FRNS). Their audiologic tests, including Pure-tone Audiometry and Distortion-Product Otoacoustic Emission (DPOAE), were compared with the tests of the control group. In addition, the audiologic tests of the NS patients who received cyclosporine were compared with those who did not.

RESULTS

In the pure-tone audiometry, there were statistically significant differences between the IRNS, SD/FRNS, and control groups at 2000, 4000 Hz, and pure-tone average (PTA). Hearing levels of the SD/FRNS group at 2000, 4000 Hz, and PTA were higher than those of the control group. At 6000 Hz in pure-tone audiometry, there was a very weak positive correlation between the hearing level and the number of relapses. At 250 Hz and PTA, hearing levels of the group that received cyclosporine were higher compared to the group that did not receive it. In DPOAE, there was no significant difference between the groups according to the severity of the disease and the use of cyclosporine.

CONCLUSION

During the follow-up of the patients with NS, their hearing functions should be questioned, especially in patients with SD/FRNS and receiving cyclosporine treatment.

High detection rate for disease-causing variants in a cohort of 30 Iranian pediatric steroid resistant nephrotic syndrome cases

BACKGROUND

Steroid resistant nephrotic syndrome (SRNS) represents a significant renal disease burden in childhood and adolescence. In contrast to steroid sensitive nephrotic syndrome (SSNS), renal outcomes are significantly poorer in SRNS. Over the past decade, extensive genetic heterogeneity has become evident while disease-causing variants are still only identified in 30% of cases in previously reported studies with proportion and type of variants identified differing depending on the age of onset and ethnical background of probands. A genetic diagnosis however can have implications regarding clinical management, including kidney transplantation, extrarenal disease manifestations, and, in some cases, even causal therapy. Genetic diagnostics therefore play an important role for the clinical care of SRNS affected individuals.

METHODOLOGY AND RESULTS

Here, we performed NPHS2 Sanger sequencing and subsequent exome sequencing in 30 consanguineous Iranian families with a child affected by SRNS with a mean age of onset of 16 months. We identified disease-causing variants and one variant of uncertain significance in 22 families (73%), including variants in NPHS1 (30%), followed by NPHS2 (20%), WT1 (7%) as well as in NUP205, COQ6, ARHGDIA, SGPL1, and NPHP1 in single cases. Eight of these variants have not previously been reported as disease-causing, including four NPHS1 variants and one variant in NPHS2, ARHGDIA, SGPL1, and NPHP1 each.

CONCLUSION

In line with previous studies in non-Iranian subjects, we most frequently identified disease-causing variants in NPHS1 and NPHS2. While Sanger sequencing of NPHS2 can be considered as first diagnostic step in non-congenital cases, the genetic heterogeneity underlying SRNS renders next-generation sequencing based diagnostics as the most efficient genetic screening method. In accordance with the mainly autosomal recessive inheritance pattern, diagnostic yield can be significantly higher in consanguineous than in outbred populations.

Congenital nephrotic syndrome

Congenital nephrotic syndrome (CNS), a challenging form of nephrotic syndrome, is characterized by massive proteinuria, hypoalbuminemia, and edema. Extensive leakage of plasma proteins is the main feature of CNS. Patients can be diagnosed in utero or during the first few weeks of life, usually before three months. The etiology of CNS can be related to either genetic or nongenetic etiologies. Pathogenic variants in NPHS1, NPHS2, LAMB2, WT1, and PLCE1 genes have been implicated in this disease. The clinical course is complicated by significant edema, infections, thrombosis, hypothyroidism, failure to thrive, and others. Obtaining vascular access, frequent intravenous albumin infusions, diuretic use, infection prevention, and nutritional support are the mainstay management during their first month of life. The best therapy for these patients is kidney transplantation. CNS diagnosis and treatment continue to be a challenge for clinicians. This review increases the awareness about the pathogenesis, diagnosis, and management of CNS patients.

Involvement of Hemopexin in the Pathogenesis of Proteinuria in Children with Idiopathic Nephrotic Syndrome

Hemopexin (Hpx) is considered a factor in the pathogenesis of idiopathic nephrotic syndrome (INS). The aim of the study was to evaluate the serum and urine values of Hpx (sHpx and uHpx) in children with INS, analyze the role of Hpx, and assess its usefulness as a marker of the disease course. 51 children with INS and 18 age-matched controls were examined. Patients were divided into subgroups depending on the number of relapses (group IA-the first episode of INS, group IB-with relapses) and according to method of treatment (group IIA treated with gluco-corticosteroids (GCS), group IIB treated with GCS and other immunosuppressants). Hpx concentrations were determined by enzyme-linked immunosorbent assay (ELISA). sHpx and uHpx values in relapse were elevated in the whole INS group versus controls (p < 0.000). In remission their levels decreased, but still remained higher than in the control group (p < 0.000). In group IB uHpx levels were increased during remission as compared to group IA (p < 0.006). No significant impact of immuno-suppressants on sHpx was observed, but uHpx excretion in group IIA was higher in relapse (p < 0.026) and lower in remission (p < 0.0017) as compared to group IIB. The results suggest the role of Hpx in the pathogenesis of INS. Hpx may be a useful indicator for continuation of treatment, but it requires confirmation by further controlled studies.

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.

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.