scholarly journals TBC1D8B Mutations Implicate RAB11-Dependent Vesicular Trafficking in the Pathogenesis of Nephrotic Syndrome

2019 ◽  
Vol 30 (12) ◽  
pp. 2338-2353 ◽  
Author(s):  
Lina L. Kampf ◽  
Ronen Schneider ◽  
Lea Gerstner ◽  
Roland Thünauer ◽  
Mengmeng Chen ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Slit Diaphragm ◽  
Missense Mutations ◽  
Loss Of Function ◽  
Cellular Functions ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Whole Exome ◽  
Immortalized Cell

BackgroundMutations in about 50 genes have been identified as monogenic causes of nephrotic syndrome, a frequent cause of CKD. These genes delineated the pathogenetic pathways and rendered significant insight into podocyte biology.MethodsWe used whole-exome sequencing to identify novel monogenic causes of steroid-resistant nephrotic syndrome (SRNS). We analyzed the functional significance of an SRNS-associated gene in vitro and in podocyte-like Drosophila nephrocytes.ResultsWe identified hemizygous missense mutations in the gene TBC1D8B in five families with nephrotic syndrome. Coimmunoprecipitation assays indicated interactions between TBC1D8B and active forms of RAB11. Silencing TBC1D8B in HEK293T cells increased basal autophagy and exocytosis, two cellular functions that are independently regulated by RAB11. This suggests that TBC1D8B plays a regulatory role by inhibiting endogenous RAB11. Coimmunoprecipitation assays showed TBC1D8B also interacts with the slit diaphragm protein nephrin, and colocalizes with it in immortalized cell lines. Overexpressed murine Tbc1d8b with patient-derived mutations had lower affinity for endogenous RAB11 and nephrin compared with wild-type Tbc1d8b protein. Knockdown of Tbc1d8b in Drosophila impaired function of the podocyte-like nephrocytes, and caused mistrafficking of Sns, the Drosophila ortholog of nephrin. Expression of Rab11 RNAi in nephrocytes entailed defective delivery of slit diaphragm protein to the membrane, whereas RAB11 overexpression revealed a partial phenotypic overlap to Tbc1d8b loss of function.ConclusionsNovel mutations in TBC1D8B are monogenic causes of SRNS. This gene inhibits RAB11. Our findings suggest that RAB11-dependent vesicular nephrin trafficking plays a role in the pathogenesis of nephrotic syndrome.

scholarly journals GAPVD1 and ANKFY1 Mutations Implicate RAB5 Regulation in Nephrotic Syndrome

2018 ◽  
Vol 29 (8) ◽  
pp. 2123-2138 ◽  
Author(s):  
Tobias Hermle ◽  
Ronen Schneider ◽  
David Schapiro ◽  
Daniela A. Braun ◽  
Amelie T. van der Ven ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Binding Affinity ◽  
Ectopic Expression ◽  
Physical Interaction ◽  
Missense Mutations ◽  
Wild Type ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Whole Exome

BackgroundSteroid-resistant nephrotic syndrome (SRNS) is a frequent cause of CKD. The discovery of monogenic causes of SRNS has revealed specific pathogenetic pathways, but these monogenic causes do not explain all cases of SRNS.MethodsTo identify novel monogenic causes of SRNS, we screened 665 patients by whole-exome sequencing. We then evaluated the in vitro functional significance of two genes and the mutations therein that we discovered through this sequencing and conducted complementary studies in podocyte-like Drosophila nephrocytes.ResultsWe identified conserved, homozygous missense mutations of GAPVD1 in two families with early-onset NS and a homozygous missense mutation of ANKFY1 in two siblings with SRNS. GAPVD1 and ANKFY1 interact with the endosomal regulator RAB5. Coimmunoprecipitation assays indicated interaction between GAPVD1 and ANKFY1 proteins, which also colocalized when expressed in HEK293T cells. Silencing either protein diminished the podocyte migration rate. Compared with wild-type GAPVD1 and ANKFY1, the mutated proteins produced upon ectopic expression of GAPVD1 or ANKFY1 bearing the patient-derived mutations exhibited altered binding affinity for active RAB5 and reduced ability to rescue the knockout-induced defect in podocyte migration. Coimmunoprecipitation assays further demonstrated a physical interaction between nephrin and GAPVD1, and immunofluorescence revealed partial colocalization of these proteins in rat glomeruli. The patient-derived GAPVD1 mutations reduced nephrin-GAPVD1 binding affinity. In Drosophila, silencing Gapvd1 impaired endocytosis and caused mistrafficking of the nephrin ortholog.ConclusionsMutations in GAPVD1 and probably in ANKFY1 are novel monogenic causes of NS. The discovery of these genes implicates RAB5 regulation in the pathogenesis of human NS.

Whole-Exome Sequencing Solved over 2-Decade Kidney Disease Enigma

Nephron ◽  
2021 ◽  
pp. 1-6
Author(s):  
Suramath Isaranuwatchai ◽  
Ankanee Chanakul ◽  
Chupong Ittiwut ◽  
Chalurmpon Srichomthong ◽  
Vorasuk Shotelersuk ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Kidney Disease ◽  
Exome Sequencing ◽  
Whole Exome Sequencing ◽  
Treatment Plan ◽  
Unknown Etiology ◽  
Pediatric Case ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Whole Exome

Chronic kidney disease of unknown etiology (CKDu) has been a problem in renal practice as indefinite diagnosis may lead to inappropriate management. Here, we report a 54-year-old father diagnosed with CKDu at 33 years old and his 8-year-old son with steroid-resistant nephrotic syndrome. Using whole-exome sequencing, both were found to be heterozygous for c.737G>A (p.Arg246Gln) in LMX1B. The diagnosis of LMX1B-associated nephropathy has led to changes in the treatment plan with appropriate genetic counseling. The previously reported cases with this particular mutation were also reviewed. Most children with LMX1B-associated nephropathy had nonnephrotic proteinuria with normal renal function. Interestingly, our pediatric case presented with steroid-resistant nephrotic syndrome at 8 years old and progressed to ESRD requiring peritoneal dialysis at the age of 15 years. Our report emphasized the need of genetic testing in CKDu for definite diagnosis leading to precise management.

scholarly journals Reverse Phenotyping after Whole-Exome Sequencing in Steroid-Resistant Nephrotic Syndrome

2019 ◽  
Vol 15 (1) ◽  
pp. 89-100 ◽  
Author(s):  
Samuela Landini ◽  
Benedetta Mazzinghi ◽  
Francesca Becherucci ◽  
Marco Allinovi ◽  
Aldesia Provenzano ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Exome Sequencing ◽  
Whole Exome Sequencing ◽  
Clinical Signs ◽  
Long Term Outcome ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Pathogenic Variants ◽  
Whole Exome ◽  
Steroid Sensitive

Background and objectivesNephrotic syndrome is a typical presentation of genetic podocytopathies but occasionally other genetic nephropathies can present as clinically indistinguishable phenocopies. We hypothesized that extended genetic testing followed by reverse phenotyping would increase the diagnostic rate for these patients.Design, setting, participants, & measurementsAll patients diagnosed with nephrotic syndrome and referred to our center between 2000 and 2018 were assessed in this retrospective study. When indicated, whole-exome sequencing and in silico filtering of 298 genes related to CKD were combined with subsequent reverse phenotyping in patients and families. Pathogenic variants were defined according to current guidelines of the American College of Medical Genetics.ResultsA total of 111 patients (64 steroid-resistant and 47 steroid-sensitive) were included in the study. Not a single pathogenic variant was detected in the steroid-sensitive group. Overall, 30% (19 out of 64) of steroid-resistant patients had pathogenic variants in podocytopathy genes, whereas a substantial number of variants were identified in other genes, not commonly associated with isolated nephrotic syndrome. Reverse phenotyping, on the basis of a personalized diagnostic workflow, permitted to identify previously unrecognized clinical signs of an unexpected underlying genetic nephropathy in a further 28% (18 out of 64) of patients. These patients showed similar multidrug resistance, but different long-term outcome, when compared with genetic podocytopathies.ConclusionsReverse phenotyping increased the diagnostic accuracy in patients referred with the diagnosis of steroid-resistant nephrotic syndrome.

scholarly journals Mutations in PRDM15 Are a Novel Cause of Galloway-Mowat Syndrome

2021 ◽  
Vol 32 (3) ◽  
pp. 580-596
Author(s):  
Nina Mann ◽  
Slim Mzoughi ◽  
Ronen Schneider ◽  
Susanne J. Kühl ◽  
Denny Schanze ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Transcriptional Activation ◽  
Homozygosity Mapping ◽  
Steroid Resistant ◽  
Brain Anomalies ◽  
Whole Exome ◽  
Skeletal Defects ◽  
Pcr Technology

BackgroundGalloway-Mowat syndrome (GAMOS) is characterized by neurodevelopmental defects and a progressive nephropathy, which typically manifests as steroid-resistant nephrotic syndrome. The prognosis of GAMOS is poor, and the majority of children progress to renal failure. The discovery of monogenic causes of GAMOS has uncovered molecular pathways involved in the pathogenesis of disease.MethodsHomozygosity mapping, whole-exome sequencing, and linkage analysis were used to identify mutations in four families with a GAMOS-like phenotype, and high-throughput PCR technology was applied to 91 individuals with GAMOS and 816 individuals with isolated nephrotic syndrome. In vitro and in vivo studies determined the functional significance of the mutations identified.ResultsThree biallelic variants of the transcriptional regulator PRDM15 were detected in six families with proteinuric kidney disease. Four families with a variant in the protein’s zinc-finger (ZNF) domain have additional GAMOS-like features, including brain anomalies, cardiac defects, and skeletal defects. All variants destabilize the PRDM15 protein, and the ZNF variant additionally interferes with transcriptional activation. Morpholino oligonucleotide-mediated knockdown of Prdm15 in Xenopus embryos disrupted pronephric development. Human wild-type PRDM15 RNA rescued the disruption, but the three PRDM15 variants did not. Finally, CRISPR-mediated knockout of PRDM15 in human podocytes led to dysregulation of several renal developmental genes.ConclusionsVariants in PRDM15 can cause either isolated nephrotic syndrome or a GAMOS-type syndrome on an allelic basis. PRDM15 regulates multiple developmental kidney genes, and is likely to play an essential role in renal development in humans.

scholarly journals ADCK4 Deficiency Destabilizes the Coenzyme Q Complex, Which Is Rescued by 2,4-Dihydroxybenzoic Acid Treatment

2020 ◽  
Vol 31 (6) ◽  
pp. 1191-1211 ◽  
Author(s):  
Eugen Widmeier ◽  
Seyoung Yu ◽  
Anish Nag ◽  
Youn Wook Chung ◽  
Makiko Nakayama ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Knockout Mice ◽  
Molecular Mechanisms ◽  
Coenzyme Q ◽  
Mass Spectrometry Analysis ◽  
Dihydroxybenzoic Acid ◽  
Mitochondrial Potential ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome

BackgroundMutations in ADCK4 (aarF domain containing kinase 4) generally manifest as steroid-resistant nephrotic syndrome and induce coenzyme Q10 (CoQ10) deficiency. However, the molecular mechanisms underlying steroid-resistant nephrotic syndrome resulting from ADCK4 mutations are not well understood, largely because the function of ADCK4 remains unknown.MethodsTo elucidate the ADCK4’s function in podocytes, we generated a podocyte-specific, Adck4-knockout mouse model and a human podocyte cell line featuring knockout of ADCK4. These knockout mice and podocytes were then treated with 2,4-dihydroxybenzoic acid (2,4-diHB), a CoQ10 precursor analogue, or with a vehicle only. We also performed proteomic mass spectrometry analysis to further elucidate ADCK4’s function.ResultsAbsence of Adck4 in mouse podocytes caused FSGS and albuminuria, recapitulating features of nephrotic syndrome caused by ADCK4 mutations. In vitro studies revealed that ADCK4-knockout podocytes had significantly reduced CoQ10 concentration, respiratory chain activity, and mitochondrial potential, and subsequently displayed an increase in the number of dysmorphic mitochondria. However, treatment of 3-month-old knockout mice or ADCK4-knockout cells with 2,4-diHB prevented the development of renal dysfunction and reversed mitochondrial dysfunction in podocytes. Moreover, ADCK4 interacted with mitochondrial proteins such as COQ5, as well as cytoplasmic proteins such as myosin and heat shock proteins. Thus, ADCK4 knockout decreased the COQ complex level, but overexpression of ADCK4 in ADCK4-knockout podocytes transfected with wild-type ADCK4 rescued the COQ5 level.ConclusionsOur study shows that ADCK4 is required for CoQ10 biosynthesis and mitochondrial function in podocytes, and suggests that ADCK4 in podocytes stabilizes proteins in complex Q in podocytes. Our study also suggests a potential treatment strategy for nephrotic syndrome resulting from ADCK4 mutations.

scholarly journals Mutations in KIRREL1, a slit diaphragm component, cause steroid-resistant nephrotic syndrome

2019 ◽  
Vol 96 (4) ◽  
pp. 883-889 ◽  
Author(s):  
Ashish K. Solanki ◽  
Eugen Widmeier ◽  
Ehtesham Arif ◽  
Shailza Sharma ◽  
Ankana Daga ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Slit Diaphragm ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome

scholarly journals Polypoid Change of the Glomerular Basement Membrane in a Child with Steroid Resistant Nephrotic Syndrome and ARHGAP24 Mutation: A Case Report

2016 ◽  
Vol 9 (1) ◽  
pp. 88-93 ◽  
Author(s):  
Anna Francis ◽  
John Burke ◽  
Leo Francis ◽  
Steven McTaggart ◽  
Andrew Mallett
Keyword(s):  
Nephrotic Syndrome ◽  
Basement Membrane ◽  
Gene Product ◽  
Glomerular Basement Membrane ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Membrane Ruffling ◽  
Genes Encoding ◽  
Important Player

Background: Steroid resistant nephrotic syndrome (SRNS) is increasingly recognised to have a genetic basis following the identification of a number of mutations within genes encoding podocyte and basement membrane proteins. The ARHGAP24 gene product is a recently recognised important player in podocyte interaction with the glomerular basement membrane. The ARHGAP24 gene encodes a protein involved in regulating cell motility, membrane structure and polarity. Mutations in the gene have been shown in vitro to cause cell membrane ruffling. Case Presentation: We report a novel missense mutation in exon 4 (c.[284G>A]; p.[Arg95Gln]) of the ARHGAP24 gene in a child that presented with SRNS at four years of age. Renal biopsy demonstrated unusual polypoid changes of the glomerular basement membrane (GBM). Conclusion: We propose this novel ARHGAP24 mutation as causative for SRNS associated with unusual polypoid basement membrane changes. These biopsy findings, in association with ARHGAP24 mutation and clinical nephrotic syndrome are a novel finding. This finding may advance the understanding of ARHGAP24 gene product function.

scholarly journals Whole Exome Sequencing of Patients with Steroid-Resistant Nephrotic Syndrome

2017 ◽  
Vol 13 (1) ◽  
pp. 53-62 ◽  
Author(s):  
Jillian K. Warejko ◽  
Weizhen Tan ◽  
Ankana Daga ◽  
David Schapiro ◽  
Jennifer A. Lawson ◽  
...  
Keyword(s):  
Nephrotic Syndrome ◽  
Exome Sequencing ◽  
Whole Exome Sequencing ◽  
Genetic Diagnosis ◽  
Congenital Nephrotic Syndrome ◽  
Causative Mutation ◽  
Steroid Resistant ◽  
Steroid Resistant Nephrotic Syndrome ◽  
Whole Exome ◽  
Panel Sequencing

Background and objectivesSteroid-resistant nephrotic syndrome overwhelmingly progresses to ESRD. More than 30 monogenic genes have been identified to cause steroid-resistant nephrotic syndrome. We previously detected causative mutations using targeted panel sequencing in 30% of patients with steroid-resistant nephrotic syndrome. Panel sequencing has a number of limitations when compared with whole exome sequencing. We employed whole exome sequencing to detect monogenic causes of steroid-resistant nephrotic syndrome in an international cohort of 300 families.Design, setting, participants, & measurementsThree hundred thirty-five individuals with steroid-resistant nephrotic syndrome from 300 families were recruited from April of 1998 to June of 2016. Age of onset was restricted to <25 years of age. Exome data were evaluated for 33 known monogenic steroid-resistant nephrotic syndrome genes.ResultsIn 74 of 300 families (25%), we identified a causative mutation in one of 20 genes known to cause steroid-resistant nephrotic syndrome. In 11 families (3.7%), we detected a mutation in a gene that causes a phenocopy of steroid-resistant nephrotic syndrome. This is consistent with our previously published identification of mutations using a panel approach. We detected a causative mutation in a known steroid-resistant nephrotic syndrome gene in 38% of consanguineous families and in 13% of nonconsanguineous families, and 48% of children with congenital nephrotic syndrome. A total of 68 different mutations were detected in 20 of 33 steroid-resistant nephrotic syndrome genes. Fifteen of these mutations were novel. NPHS1, PLCE1, NPHS2, and SMARCAL1 were the most common genes in which we detected a mutation. In another 28% of families, we detected mutations in one or more candidate genes for steroid-resistant nephrotic syndrome.ConclusionsWhole exome sequencing is a sensitive approach toward diagnosis of monogenic causes of steroid-resistant nephrotic syndrome. A molecular genetic diagnosis of steroid-resistant nephrotic syndrome may have important consequences for the management of treatment and kidney transplantation in steroid-resistant nephrotic syndrome.

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