CJASN ePress. Published on April 23, 2020 as doi: 10.2215/CJN.11440919

Genetic Disorders of the Glomerular Filtration Barrier

Anna S. Li,1,2 Jack F. Ingham,1 and Rachel Lennon 1,3

Abstract 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 three 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 1Division of Cell- glomerular biology and pathophysiology. In current clinical practice, a genetic diagnosis already has important Matrix Biology and implications for management ranging from estimating the risk of disease recurrence post-transplant to the life- Regenerative changing advances in the treatment of atypical hemolytic uremic syndrome. Improving our understanding about Medicine, Wellcome Centre for Cell-Matrix the mechanistic basis of glomerular disease is required for more effective and personalized therapy options. In this Research, School of review we describe genotype and phenotype correlations for genetic disorders of the glomerular filtration barrier, Biological Sciences, with a particular emphasis on how these defects cluster by both their ontology and patterns of glomerular Faculty of Biology, pathology. Medicine and Health, CJASN ccc–ccc Manchester Academic 15: , 2020. doi: https://doi.org/10.2215/CJN.11440919 Health Science Centre, The University of Manchester, Introduction fenestrae that are 70–100 nm in diameter and covered Manchester, United . Kingdom; Defects in 80 have been found to cause by an endothelial surface layer consisting largely of 2 fi Department of disorders of the glomerular ltration barrier, with a glycocalyx that contributes to the charge-selective , rapid rise in gene discovery over the last 10 years barrier (10). The GBM is a unique basement mem- Manchester University (Figure 1). This list continues to expand with the use brane formed by secreted products from both endo- Hospitals National Health Service of next-generation sequencing in large cohorts of pa- thelial cells and podocytes during glomerulogenesis – Foundation Trust, tients who have been deeply phenotyped (1 4). Whole- (11). It is a complex gel-like structure consisting of Manchester Academic exome and whole-genome sequencing allows rapid core basement membrane components, including Health Science screening for both pathogenic and novel variants in laminin isoforms, type IV , nidogen, and Centre, Manchester, affected individuals and their families who lack a United Kingdom; and heparan sulfate proteoglycans, in addition to many 3 genetic diagnosis (5). Furthermore, advances in cell- Department of fi more less abundant structural and regulatory compo- Paediatric speci c genetic engineering techniques such as Cre-lox nents (12). Podocytes are specialized epithelial cells Nephrology, Royal recombination (6) and more recent genome-editing covering the outer aspect of the glomerular capillary. Manchester Children’s approaches with CRISPR-Cas9 (7) have enabled fo- Hospital, Manchester These cells are basally anchored to the GBM through cused in vivo and in vitro modeling of gene function. University Hospitals transmembrane receptors such as integrins and National Health These approaches can elicit mechanistic details about dystroglycans (10) and specialized cell-cell junctions Service Foundation genetic variants and cellular physiology to establish a known as slit diaphragms interconnect podocytes Trust, Manchester causal link from gene to clinical phenotype (8). Using Academic Health this pipeline from gene discovery to experimental laterally (10). Podocyte foot processes have an actin- Science Centre, modeling, our understanding of the glomerular filtra- based cytoskeleton connecting basal, lateral, and Manchester, United via Kingdom tion barrier in health and disease has been trans- apical domains linker to both cell-cell formed. This review focuses on known human genetic and cell-matrix junctions and thereby convey cues from the extracellular environment (10). Correspondence: disorders of the filtration barrier by considering the Prof. Rachel Lennon, key component parts: podocytes, endothelial cells, and Pathogenic variants in a wide range of genes with Division of Cell- fi the glomerular basement membrane. functional relevance in glomerular ltration have Matrix Biology, been identified to date. As a high-level starting point, Wellcome Centre for these genes can be classified according to their Cell-Matrix Research, fi School of Biological The Glomerular Filtration Barrier location within the three-layered ltration barrier Sciences, Faculty of The filtration barrier comprises three layers: (Figure 2). An alternative representation is demon- Biology Medicine and podocytes and endothelial cells with an intervening strated with enrichment analysis of Health, University of cellular compartment annotations for known genes Manchester, Oxford glomerular basement membrane (GBM). Together, this Road, Manchester specialized capillary wall allows selective ultrafiltration (Figure 3). This analysis demonstrates the importance M13 9PT, United while retaining circulating cells and plasma proteins. of the cellular cytoskeleton, cell-cell junctions, and Kingdom. Email: The barrier is both size selective and charge selective, extracellular matrix in genetic disorders of the filtra- Rachel.Lennon@ manchester.ac.uk as demonstrated by early studies of transferrin tion barrier. In the following sections, we demonstrate accumulation (9). Glomerular endothelial cells have how genetic discovery has highlighted particular www.cjasn.org Vol 15 December, 2020 Copyright © 2020 by the American Society of Nephrology 1 2 CJASN

role of these genes in normal glomerular function. They also reaffirm the essential role of the podocyte in the function of the filtration barrier with the majority of genes implicated in steroid-resistant nephrotic syndrome localizing to the podocyte.

Slit Diaphragm–Related Genes NPHS1 encodes , a transmembrane and a core component of the slit diaphragm. Between adjacent foot processes, nephrin molecules form homo- and hetero- dimers with its homolog Neph1 forming the slit diaphragm in a zipper-like pattern. Intracellularly, nephrin phosphoryla- tion by the tyrosine kinase Fyn leads to enhanced PI3K/Akt/ Rac pathway activation, promoting dynamic modeling of actin cytoskeleton. Nephrin interacts with (encoded by NPHS2), an integral membrane protein, and CD2-associated protein (encoded by CD2AP), an adapter protein connecting nephrin to the actin cytoskeleton as well as interacting with the PI3K/Akt pathway. Nephrin also interacts with IQ motif–containing GTPase-activating protein 1 (IQGAP1), which in turn interacts with phospho- lipase C«1 (encoded by PLCE1), a phospholipase generating downstream messengers such as such as inositol 1,4,5- NPHS1 fi trisphosphate (IP3) and diacylglycerol. was identi ed as the pathogenic gene in congenital nephrotic syndrome of the Finnish type (13). Disease-causing homozygous NPHS1 variants are common in Finland, affecting approximately Figure 1. | The rapid rise in gene discovery. Thenumberofnewgene 1 in 10,000 children. Two truncating variants (Fin-major discoveries is shown together with the cumulative total. There is rapid rise and Fin-minor) account for .94% of Finnish cases, in discoveries in the last 10 years, from 29 genes in 2009 to 87 in 2019. demonstrating a founder effect. Outside Finland, classic NPHS1 variants are rare. Missense variants are associated cellular components and biologic pathways and helped to with a milder FSGS phenotype (14). Homozygous variants NPHS2 PLCE1 build understanding about glomerular biology and patho- in and causing steroid-resistant nephrotic physiology. syndrome display genotype-phenotype correlation. Differ- ent NPHS2 variants can cause steroid-resistant nephrotic syndrome with variant-specific disease severity and onset Podocyte Genetics from early childhood to early adulthood. Truncating var- Inherited podocyte dysfunction typically manifests as iants in PLCE1 cause early onset of and pro- nephrotic syndrome, characterized by the clinical triad of gression to failure, whereas missense variants are massive proteinuria, albumin ,25 g/L, and edema. Many found in later-onset nephrotic syndrome and cause slower genetic causes of nephrotic syndrome are resistant to progression. Some individuals with PLCE1 variants were treatment with glucocorticoids, leading to the classifica- responsive to corticosteroids and immunosuppressive ther- tion of steroid-resistant nephrotic syndrome. The prog- apy. Recently, defects in proteins encoded by KIRREL1 and nosis for patients with steroid-resistant nephrotic KIRREL2, members of the NEPH family that interact with syndrome is poor and they invariably progress to kidney podocin, have also been found in children with steroid- failure. Although kidney biopsy remains an important resistant nephrotic syndrome (15,16). clinical tool for the histologic diagnosis of nephrotic Enhanced calcium influx appears to be a key factor for syndrome, the availability of has enabled a mediating podocyte injury and is associated with mono- further layer of classification. Overall the most frequent genic causes of steroid-resistant nephrotic syndrome. Tran- histologic pattern observed in steroid-resistant nephrotic sient receptor potential channel C6 (encoded by TRPC6)is syndrome is FSGS, whereas in early-onset steroid-resistant aslitdiaphragm–associated calcium channel and mechan- nephrotic syndrome diffuse mesangial sclerosis is a fre- ical stretch sensor. A heterozygous gain-of-function variant quent finding. However, there is significant overlap between enhances TRPC6-mediated calcium signal amplitude am- histopathology and ultrastructural patterns associated with plification, resulting in prolonged channel activation. TRPC6 pathogenic variants causing glomerular disease (Figure 4). is also associated with angiotensin II–mediated calcium These findings demonstrate the precision of genetic test- influx and apoptosis, leading to podocyte loss (17). Variants ing compared with kidney biopsies for reaching a diag- in other genes such as NPHS2, ACTN4,andAPOL1 also nosis but also indicate that a range of genetic defects result in calcium overload and podocyte injury, possibly via will potentially share similar mechanisms of injury. The TRPC6 hyperactivity (18). discovery of pathogenic variants causing steroid-resistant Podocalyxin is a transmembrane sialoglycoprotein local- nephrotic syndrome provides important insights into the ized to the podocyte apical surface and acts as an antiadhesin CJASN 15: ccc–ccc, December, 2020 Glomerular Genetics, Li et al. 3

Figure 2. | Disease-causing genes can be categorized by cellular localization. Electron microscopy from the kidney of an 8-week-old BL6/C57 mouse. The glomerular filtration barrier is shown with annotation. The genes known to cause glomerular filtration barrier dysfunction are listed and categorized by localization. that maintains the opening of the slit diaphragm through of the actin cytoskeleton have been identified as the causes charge repulsion. Autosomal dominant variants in podoca- of steroid-resistant nephrotic syndrome. Myosin 1E, enco- lyxin, encoded by PODXL, cause adolescence- to adult-onset ded by MYO1E, is an actin-based molecular motor and a key steroid-resistant nephrotic syndrome with incomplete dis- component of the podocyte cytoskeleton that interacts with ease penetrance (19). PTPRO encodes a tyrosine phosphatase the slit diaphragm complex. Podocytes expressing defective expressed at the apical membrane of the foot processes. MYO1E could not efficiently assemble actin cables along Tyrosine phosphorylation of the slit diaphragm compo- new cell-cell junctions (22). a-Actinin-4 is an actin-filament nents nephrin and ZO-1 alters their association with other crosslinking protein encoded by ACTN4. Pathogenic vari- slit diaphragm proteins. Notably, patients harboring ants in its actin-binding domain increase its binding affinity, PTPRO variants showed partial response to corticosteroid resulting in a stiffened and more brittle actin network and cyclosporin combination therapy (20). and making the podocyte vulnerable to detachment under environmental mechanical stress (23). Inverted formin 2, encoded by INF2, nucleates actin filaments and promotes Cytoskeletal Genes actin elongation, as well as accelerating F-actin depolymer- Podocyte cells are highly differentiated and polarized. ization and filament severing. Variants in INF2 lead to Their architecture and morphology is integral to function as aberrant regulation of actin turnover and restructuring. part of the glomerular filtration barrier. Healthy podocytes INF2 also binds to and is regulated by the Rho GTPase have an arborized shape characterized by multiple branch- Cdc42. The Rho family GTPases RhoA, Rac1, and Cdc42 ing projections forming the foot processes (21). A hallmark signaling pathways are implicated in the pathogenesis of feature of nephrotic syndrome is the loss of podocyte other monogenic variants causing steroid-resistant nephrotic arborization and foot-process effacement, and this is asso- syndrome. Under the stress response, podocytes switch ciated with significant cytoskeletal remodeling. The slit from a RhoA-dependent stationary state to a Cdc42- and diaphragm complex is inextricably connected to the highly Rac1-dependent migratory state. Rho GTPase–activating dynamic actin cytoskeleton, transducing signals to affect protein 24, encoded by ARHGAP24,activatesRhoA, and coordinate podocyte structure and function. Variants leading to downstream suppression of lamellipodia formation in a number of genes encoding modulators and components andcellspreading.Thisfunctionisimpairedinautosomal 4 CJASN

Figure 3. | Disease-causing genes are connected in their biological roles. AGene Ontology enrichment analysis was performed for the 87 genes described in this review. We used clusterProfiler (59), which is an open-source tool useful for highlighting the predominant biologic roles in a collection of genes, andwe selected the cellularcompartment ontology.This highlights the importance of the podocyte, extracellular matrix, and nucleus.

dominant ARHGAP24 variants because both wild-type ITSN2, MAGI2 variants were also found to be pathogenic in and mutated proteins homodimerize and heterodimerize partial treatment-sensitive nephrotic syndrome. These genes (24). In patients with homozygous ARHGDIA variants, encode a cluster of proteins that either physically or func- the defective encoded protein Rho GDP dissociation tionally interact to regulate RhoA/Rac1/Cdc42 activation. inhibitor a fails to interact with Rac1 and Cdc42, resulting Interestingly, glucocorticoid treatment abolished the effect of in increased GDP-bound Rac1 and Cdc42 activity. KANK DLC1 or CDK20 knockdown on RhoA activation in vitro (28). 1/2/4 genes encoding kidney ankyrin repeat-containing proteins also harbor pathogenic variants (25). KANK2 interacts with ARHGDIA whereas KANK1 colocalizes Transcription Factors and Nuclear and Mitochondrial with synaptopodin encoded by SYNPO.Synaptopodin Genes is a podocyte-specific, actin-binding protein and is antag- Pathogenic variants in transcription factors controlling onized by TRPC5- and TRPC6-mediated calcium influx. the development of urogenital system can cause a wide Loss-of-function variants in synaptopodin result in the spectrum of systemic syndromes with kidney involvement. loss of stress fibers and reduction in RhoA abundance and WT1 was the first mutated gene discovered in steroid- activity (26). Membrane-associated guanylate kinase in- resistant nephrotic syndrome. Variants in WT1 cause verted 2, encoded by MAGI2, directly binds to the cyto- Denys–Drash syndrome and Frasier syndrome associated solic tail of nephrin and regulates actin cytoskeleton via with urogenital abnormalities, malignant Wilms tumor, RhoA. MAGI2 variants have been found in patients with and gonadoblastoma. Missense variants affecting the WT1 congenital steroid-resistant nephrotic syndrome (27). Re- DNA-binding site are associated with diffuse mesangial cently, together with DLC1, CDK20, TNS2, ITSN1,and sclerosis, early-onset steroid-resistant nephrotic syndrome, CJASN 15: ccc–ccc, December, 2020 Glomerular Genetics, Li et al. 5

Figure 4. | Genetic are associated with multiple patterns of glomerular pathology. In a quarter of genes encoding cellular com- partment proteins, mutations result in glomerular basement membrane (GBM) defects as well as FSGS and/or diffuse mesangial sclerosis (DMS). Mutations in twogenes, INF2 and DGKE, are associatedwith FSGS, GBM defects, andthrombotic microangiopathy (TMA). Manygene mutations also result in other pathologic patterns such as minimal change disease, collapsing glomerulopathy, membranoproliferative GN, mesangial proliferation, and tubular dilation. and rapid progression to . Risk of Wilms to early-onset steroid-resistant nephrotic syndrome and tumor is associated with truncating variants and late- intellectual impairment, mediated by dysregulation of onset steroid-resistant nephrotic syndrome. Intronic var- VEGF synthesis. iants usually present with as isolated childhood-onset Pathogenic variants in genes encoding several members steroid-resistant nephrotic syndrome and slower progres- of the nuclear pore complexes have been identified, in- sion of kidney impairment (29). Paired box protein 2, cluding NUP93, NUP25, NUP107, NUP85, NUP133,and encoded by PAX2, is another transcription factor with a NUP160. Nuclear pore complexes are large macromolecu- central role in kidney development. Variants in PAX2 lead lar assemblies in the nuclear envelope which mediate the to dysregulation in PAX2 targets including WT1,resulting transport of proteins, , and RNP particles between in disrupted podocyte and foot process development (30). the cytoplasm and the nucleus. Of interest, in patients with LMX1B encodes LIM homeobox transcription factor 1b NUP93 variants, some had partial response to corticoste- which regulates slit diaphragm genes. Variants in LMX1B roid and cyclosporin treatment (31). cause steroid-resistant nephrotic syndrome in isolation Genetic mutations causing mitochondrial dysfunction or in association with nail–patella syndrome. Variants in may be present in the nuclear or mitochondrial genome. MAFB encoding MAF bZIP transcription factor B cause Mutations in mitochondrial gene MTTL1 causes mitochon- adolescence- to adult-onset steroid-resistant nephrotic drial encephalomyopathy, lactic acidosis, and strokelike syndrome in association with Duane retraction syndrome, episodes (known as MELAS); diabetes; deafness; and characterized by impaired horizontal eye movement. steroid-resistant nephrotic syndrome. Steroid-resistant ne- Variants in E2F3, encoding E2F transcription factor, leads phrotic syndrome has also been reported in association 6 CJASN

with a case of neuropathy, ataxia, retinitis pigmentosa located, and the less abundant a1a2a1(IV) is adjacent to syndrome (known as NARP) caused by in glomerular endothelial cells. COL4A5 is located on the X mitochondrial gene MT-ATP6 (32). Variants in enzymes , whereas COL4A3 and COL4A4 are linked on involved in the coenzyme Q10 (CoQ10) biosynthesis chromosome 2. is caused by X-linked fi COL4A5 COL4A3/4 pathway in the mitochondria result in CoQ10 de ciency or recessive variants. Because most and may present with abnormalities in multiple systems pathogenic variants prevent assembly of the trimer, a variant including encephalopathy, neuromuscular involvement, in one gene will lead to absence or inadequate assembly of and nephrotic syndrome. Importantly, early initiation of all chains. Clinically, Alport syndrome is characterized by CoQ10 supplementation has been reported to improve , proteinuria, and progressive decline in kidney kidney phenotype (33). function. There is also sensorineural deafness and ocular manifestations such as anterior lenticonus, posterior cata- racts, and corneal dystrophy. Electron microscopy shows Complex Genetic Associations splitting and lamination of the GBM; this is thought to be due Rather than following the Mendelian mode of inheri- to extensive injury and remodeling of the GBM, giving it its tance, the APOL1 gene (encoding apolipoprotein L1) displays characteristic “basket-weave” appearance. more complex risk associations with development of FSGS, Within the large number of COL4A3–5 variants associ- nephrotic syndrome, and CKD with striking racial dispar- ated with , a wide spectrum of disease ity. From genome-wide association studies, two indepen- phenotypes and pathology has been observed. This ranges dent variants in the APOL1 gene have been found to from classic Alport syndrome, to the more slowly pro- associate with FSGS and hypertensive kidney failure. These gressive CKD in heterozygous COL4A3–5 variants associ- variants are common in populations of African descent but ated with FSGS, to clinically nonprogressive thin basement absent in populations of European descent and appear to be membrane nephropathy (Figure 4) (36). positively selected in recent evolution history. Experimentally, Although the link between genetic variants encoding type the kidney disease–associated ApoL1 variants were able to IV collagen chains and rare kidney disease is well estab- lyse the parasite Trypanosoma brucei rhodesiense, suggesting lished, recent large genetic cohort studies suggest COL4A resistance to infection as the selection pressure (34). genes have a role in diseases that are much more common. Also based on genome-wide analyses, GPC5 encoding Variants in COL4A genes have been found to be associated glypican 5, a member of the heparin sulfate proteoglycan with CKD, diabetic nephropathy, cardiovascular disease, (HSPG) family, was also identified as a risk gene for nephrotic and stroke (38–42). This is perhaps representative of the syndrome and conferred susceptibility to damage in di- organ-specific function of basement membranes and the abetic kidney disease. Glypican 5 was shown to localize to role of the different type IV collagen isoforms. the endothelial cells and podocytes in the human kidney. It The integrin a3b1 heterodimer links the podocyte to is known to play a role in binding growth factors such as the laminin network in the GBM and is the most highly fibroblast growth factor 2, which has been implicated as expressed integrin on the podocyte cell surface (43). The a3 a potential damaging signal in nephrotic syndrome (35). chain is encoded by ITGA3 and pathogenic variants have been found to cause congenital nephrotic syndrome, inter- Basement Membrane Genes stitial lung disease, and epidermolysis bullosa. Kidney Laminin-521 is the major laminin isoform in GBM. It is histology in these cases revealed profoundly abnormal a cruciform, heterotrimeric glycoprotein composed of the basement membranes, FSGS, and tubular atrophy (44). The laminin a5, b2, and g1 chains. During glomerulogenesis, a6b4 integrin also binds to laminin networks and stabi- laminin-521 trimers are secreted from podocytes and lizes adhesions in hemidesmosomes. A homozygous var- endothelial cells and polymerize in the extracellular iant in ITGB4 encoding the b4chainhasbeenidentified matrix to form lattice-like networks on each edge of the in a case of congenital nephrotic syndrome with FSGS, GBM. Laminin also serves as a ligand for cellular recep- epidermolysis bullosa, and pyloric atresia (45). GPC5 tors enabling cell adherence and signaling (36). Homozy- encodes glypican 5, a member of the HSPG family, which gous variants in LAMB2, the gene encoding laminin-b2, was identified as a risk gene conferring susceptibility for causes Pierson syndrome which is characterized by nephrotic syndrome and diabetic nephropathy (35,46). congenital nephrotic syndrome with diffuse mesangial CD151 is a transmembrane tetraspanin broadly expressed sclerosis, neurodevelopmental delay, and ocular abnor- by many cell types. Tetraspanins form membrane com- malities including microcoria and hypoplasia of the ciliary plexes on the base of podocyte foot processes along the and pupillary muscles. Recently, three homozygous var- GBM and allow clustering of associated proteins such as iants were found in LAMA5 encoding laminin-a5, which integrins and kinases, therefore enabling cellular signal may have contributed to the development in nephrotic transduction and cell-matrix adhesion (47). A homozy- syndrome in pediatric patients (37). gous variant in CD151 was detected in three patients with Type IV collagen is another structural component of the kidney failure. Electron microscopy revealed splitting of GBM. There are six collagen IV a-chains encoded by the the tubular basement membrane along with reticulation genes COL4A1–6.Thea-chains assemble into trimers in and fragmentation of the GBM (48). the endoplasmic reticulum, resulting in three distinct isoforms: a1a2a1, a3a4a5, and a5a6a5. Once released into the extracellular matrix, they polymerize to form Genes Affecting Endothelial Cell Function collagen IV hexameric networks. The mature collagen IV Dysregulation and overactivation of the alternative com- network in the GBM is a3a4a5(IV), which is centrally plement pathway cause endothelial damage and underlie CJASN 15: ccc–ccc, December, 2020 Glomerular Genetics, Li et al. 7

the pathogenesis of atypical hemolytic uremic syndrome caused by genetic abnormalities are resistant to glucocor- (aHUS). Histologically, this disease process is characterized ticoid and immunosuppressive therapy, early diagnosis by thrombotic microangiopathy, with glomerular capillary can avoid their unnecessary use. On the other hand, wall thickening, endothelial swelling, and subendothelial patients with variants in NUP93, PTPRO, PLCE1, DLC1, accumulation of material. Of all aHUS cases, 50% are DLC1, CDK20, TNS2, ITSN1, ITSN2,andMAGI2 achieved associated with genetic abnormalities in factor H, factor I, partial remission with glucocorticoid and/or immuno- membrane cofactor protein, thrombomodulin, C3, and suppression, and this could prompt a future trial of treatment factor B. Notably, 3% of patients with aHUS carry more based on patient genotype. Understanding the genetic than one mutated complement gene (49). basesofdiseasehasalsoyielded effective treatments for fi – Noncomplement genes have also been found to harbor CoQ10 de ciency related nephrotic syndrome and aHUS. variants associated with the development of aHUS, in- Eculizumab, a humanized mAb against C5, has revolu- cluding two genes associated with podocyte pathology and tionized the management of aHUS. Treatment with steroid-resistant nephrotic syndrome. Homozygous or eculizumab is able to control disease activity and preserve compound heterozygous variants in DGKE are linked to kidney function in complement-associated aHUS. 1%–5% of aHUS cases, all presenting at ,12 months of age. In addition, although patients with steroid-resistant In endothelial cells, DGK« inactivates diacylglycerols nephrotic syndrome who have a confirmed genetic diag- and defective DGK« leads to increased protein kinase C nosis have increased risks of disease progression toward activity and endothelial cell activation. Interestingly, a kidney failure, their risks of recurrence after kidney trans- subset of the children developed nephrotic syndrome plant are extremely low compared with those without 3–5 years after the onset of aHUS, a very rare event not (30%–50% risk) (1,55,56). Genetic diagnosis is also impor- usually seen with other forms of aHUS (50). Finally, variants tant in evaluating family members for living kidney in INF2, another gene related to steroid-resistant nephrotic donation, especially in cases of complex genetic associa- syndrome, were found in familial aHUS or post-transplant tions such as APOL1 and complement genes. However, thrombotic microangiopathy in the presence of common underlying genetic causes have only been identified in aHUS risk haplotypes (51). approximately 30% of steroid-resistant nephrotic syn- drome and 50% of aHUS. Better understanding of the biology of the glomerular filtration barrier and further Relative Contribution of Genetic Variants to Disease screening of large population cohorts will undoubtedly Several large cohort studies have identified underlying increase the yield of genetic testing for reaching a molecular genetic causes for childhood and early adult–onset steroid- diagnosis. resistant nephrotic syndrome or FSGS in approximately Much hope has been placed upon gene therapy in genetic 30% of cases (1–4). Distribution of causative genes and disorders. Studies showing feasibility and proof of princi- prevalence of monogenic diseases in these cohorts strongly ple have been undertaken in Alport mice. Incorporating correlated with age of onset. The most frequently mutated collagen a3a4a5(IV) chains after initial assembly via acti- genes were NPHS1, NPHS2, WT1,andCOL4A3/4/5;a vation by a tetracycline induced transgene-delayed pro- significant but less prominent group of contributors in- teinuria (57). This suggests a possible target for genetic cluded LAMB2, SMARCAL1, PLCE1, INF2, ADCK4, INF2, rescue in Alport syndrome. In fact, prior research showed a TRPC6,andCOQ2 (1–4). In two of the largest international transgene was able to rescue Col4a32/2 mice, which had pediatric cohorts, genetic causes were found in close to 70% an Alport phenotype, resulting in normal levels of pro- of congenital nephrotic syndrome cases (age ,3 months), teinuria after 6 months of follow-up (58). There remain 35%–50% of infantile onset (3–12 months), 21%–25% of many hurdles to overcome before this treatment modality early childhood onset (1–6 years), 15%–19% in late child- could be attempted in a human model, including ethical hood onset (6–12 years), and 10%–16% in adolescent onset considerations and vector transport. (13–20 years) cases (1,2). In adults, mutations in COL4A3/4/5 were the commonest genetic abnormalities found in FSGS (55%) (52,53) and in a large heterogenous CKD cohort (30% of pathogenic variants identified) (42). Summary Our ability to reach a molecular diagnosis for children and adults with glomerular disease has been transformed Current and Future Therapies over the past three decades due to genetic discoveries. The Because defects in the glomerular filtration barrier result expanding list of genetic disorders is also providing in albuminuria, conventional therapy relies on (1) renin- important insight into the underlying biology of the angiotensin-aldosterone system (RAAS) blockade to reduce glomerular filtration barrier. The ontologic clustering of proteinuria, (2) optimization of kidney disease risk factors genes highlights the important role of the podocyte silt such as BP control, and (3) RRT with or trans- diaphragm, the cytoskeleton, and its interaction with the plantation. In Alport syndrome, early initiation of RAAS GBM. These may represent the importance of these spe- blockade delays kidney failure by a median of 13 years (54). cialized structures for sensing and responding to mechan- In addition, a genetic diagnosis helps to better understand ical strain from capillary flow, because our most the genotype-phenotype correlation of diseases and to effective treatment for these disorders (RAAS blockade) stratify patients for management and prognosis. Detection reduces capillary hydrostatic pressure. The endothelial cell of a genetic variant known to associate with extrarenal genetics highlights the susceptibility of the glomerular manifestations also prompts screening for these features endothelium to complement dysregulation and the reso- (Table 1). Because most cases of nephrotic syndrome lution of these mechanisms has led to highly effective 8 CJASN

Table 1. Genetic mutations associated with extrarenal manifestations

Gene Associated Extrarenal Manifestations

WT1 Denys–Drash syndrome: ambiguous genitalia, Wilms tumor, urogenital abnormalities Frasier syndrome: ambiguous genitalia, gonadoblastoma LMX1B Nail-patella syndrome: hypoplastic nails, absent patellae, skeletal abnormalities, glaucoma SMARCAL1 Schimke immuno-osseous dysplasia: short stature, lumbar lordosis, T-cell immunodeficiency, skin hyperpigmentation, cerebral ischemia E2F3 Mental retardation NXF5 Heart block PAX2 Coloboma, hearing impairment LMNA Familial partial lipodystrophy WDR73 Galloway-Mowat syndrome: microcephaly, developmental delay, seizures, hiatal hernia, optic KEOPS complex (OSGEP, TP53RK, atrophy, movement disorders, intellectual disability TPRKB, LAGE3) MAFB Duane retraction syndrome: eye movement anomaly MYH9 Epstein syndrome: mild , with giant INF2 Charco–Marie–Tooth disease: chronic peripheral motor and sensory neuropathies ARHGDIA Seizures, cortical blindness KAT2B Cardiomyopathy COQ2 Coenzyme Q10 deficiency, progressive encephalomyopathy COQ6 Coenzyme Q10 deficiency, sensorineural hearing loss PDSS2 Leigh syndrome: coenzyme Q10 deficiency, hypotonia, seizures, ataxia, deafness, growth retardation MTTL1 MELAS syndrome: mitochondrial encephalomyopathy, lactic acidosis, strokelike episodes, diabetes, deafness MT-ATP6 NARP syndrome: neuropathy, ataxia, retinitis pigmentosa SCARB2 Action myoclonus–renal failure syndrome: myoclonus, seizures, tremor, sensorineural hearing loss ZMPSTE24 Mandibuloacral dysplasia: mandibular and clavicular hypoplasia, acro-osteolysis, cutaneous atrophy, partial lipodystrophy PMM2 Congenital defect of glycosylation SPGL1 SPL insufficiency syndrome: fetal hydrops, primary adrenal insufficiency, neurologic deterioration, immunodeficiency, acanthosis, endocrine abnormalities LAMB2 Pierson syndrome: ocular abnormalities, hypotonia, movement disorder COL4A3/4/5 Alport syndrome: sensorineural hearing loss, ocular abnormalities ITGA3 Epidermolysis bullosa, interstitial lung disease ITGB4 Epidermolysis bullosa, pyloric atresia

therapy based on a mechanistic understanding of the References underlying disease process. In the decades ahead, further 1. Trautmann A, Bodria M, Ozaltin F, Gheisari A, Melk A, Azocar M, dissection of disease mechanisms should lead to new Anarat A, Caliskan S, Emma F, Gellermann J, Oh J, Baskin E, Ksiazek J, Remuzzi G, Erdogan O, Akman S, Dusek J, Davitaia T, therapies to preserve native kidney function and prevent O¨ zkaya O, Papachristou F, Firszt-Adamczyk A, Urasinski T, Testa progression to kidney failure. S, Krmar RT, Hyla-Klekot L, Pasini A, O¨ zcakar ZB, Sallay P, Cakar N, Galanti M, Terzic J, Aoun B, Caldas Afonso A, Szymanik-Grzelak H, Lipska BS, Schnaidt S, Schaefer F; PodoNet Consortium: Spec- Acknowledgments trum of steroid-resistant and congenital nephrotic syndrome in We acknowledge Siddharth Banka (consultant clinical geneticist children: The PodoNet registry cohort. Clin J Am Soc Nephrol at Manchester University National Health Service Foundation Trust 10: 592–600, 2015 2. Sadowski CE, Lovric S, Ashraf S, Pabst WL, Gee HY, Kohl S, and clinical senior lecturer at the University of Manchester) for Engelmann S, Vega-Warner V,Fang H, Halbritter J, Somers MJ, Tan critical review of the manuscript and Craig Lawless for help with W, Shril S, Fessi I, Lifton RP, Bockenhauer D, El-Desoky S, Kari JA, the Gene Ontology enrichment analysis. Zenker M, Kemper MJ, Mueller D, Fathy HM, Soliman NA, Hildebrandt F; SRNS Study Group: A single-gene cause in 29.5% of cases of steroid-resistant nephrotic syndrome. JAmSoc Disclosures Nephrol 26: 1279–1289, 2015 Prof. Lennon acted as an advisor for the following companies 3. Bierzynska A, McCarthy HJ, Soderquest K, Sen ES, Colby E, Ding within the past 36 months: Liponext, Ono Pharmaceuticals, and WY, Nabhan MM, Kerecuk L, Hegde S, Hughes D, Marks S, Retrophin. Dr. Ingham and Dr. Li have nothing to disclose. Feather S, Jones C, Webb NJ, Ognjanovic M, Christian M, Gilbert RD, Sinha MD, Lord GM, Simpson M, Koziell AB, Welsh GI, Funding Saleem MA: Genomic and clinical profiling of a national ne- phrotic syndrome cohort advocates a precision medicine ap- Dr. Ingham is a year 3 foundation doctor undertaking academic proach to disease management. Kidney Int 91: 937–947, 2017 training supported by the University of Manchester. Prof. Lennon 4. Wang M, Chun J, Genovese G, Knob AU, Benjamin A, Wilkins is supported by the Wellcome Trust Senior Fellowship award MS, Friedman DJ, Appel GB, Lifton RP, Mane S, Pollak MR: 202860/Z/16/Z and has received research funding from Kidney Contributions of rare gene variants to familial and sporadic FSGS. J Am Soc Nephrol 30: 1625–1640, 2019 Research UK and the Medical Research Council. Dr. Li is a clinical 5. Retterer K, Juusola J, Cho MT, Vitazka P, Millan F, Gibellini F, research training fellow funded by Shire and the charity Kidneys Vertino-Bell A, Smaoui N, Neidich J, Monaghan KG, McKnight D, for Life in the form of an educational grant. Bai R, Suchy S, Friedman B, Tahiliani J, Pineda-Alvarez D, Richard CJASN 15: ccc–ccc, December, 2020 Glomerular Genetics, Li et al. 9

G, Brandt T, Haverfield E, Chung WK, Bale S: Clinical application 20. Ozaltin F, Ibsirlioglu T, Taskiran EZ, Baydar DE, Kaymaz F, of whole-exome sequencing across clinical indications. Genet Buyukcelik M, KilicBD, Balat A, Iatropoulos P,Asan E, Akarsu NA, Med 18: 696–704, 2016 Schaefer F, Yilmaz E, Bakkaloglu A; PodoNet Consortium: Dis- 6. Yarmolinsky M, Hoess R: The legacy of nat sternberg: The genesis ruption of PTPRO causes childhood-onset nephrotic syndrome. of cre-lox technology. Annu Rev Virol 2: 25–40, 2015 Am J Hum Genet 89: 139–147, 2011 7. WareJoncas Z, Campbell JM, Martı´nez-Ga´lvez G, Gendron WAC, 21. Pavensta¨dt H, Kriz W, Kretzler M: Cell biology of the glomerular Barry MA, Harris PC, Sussman CR, Ekker SC: Precision gene podocyte. Physiol Rev 83: 253–307, 2003 editing technology and applications in nephrology. Nat Rev 22. Mele C, Iatropoulos P,Donadelli R, Calabria A, Maranta R, Cassis Nephrol 14: 663–677, 2018 P, Buelli S, Tomasoni S, Piras R, Krendel M, Bettoni S, Morigi M, 8. Braun DA, Rao J, Mollet G, Schapiro D, Daugeron MC, Tan W, Delledonne M, Pecoraro C, Abbate I, Capobianchi MR, Gribouval O, Boyer O, Revy P, Jobst-Schwan T, Schmidt JM, Hildebrandt F, Otto E, Schaefer F, Macciardi F, Ozaltin F, Emre S, Lawson JA, Schanze D, Ashraf S, Ullmann JFP, Hoogstraten CA, Ibsirlioglu T, Benigni A, Remuzzi G, Noris M; PodoNet Consor- Boddaert N, Collinet B, Martin G, Liger D, Lovric S, Furlano M, tium: MYO1E mutations and childhood familial focal segmental Guerrera IC, Sanchez-Ferras O, Hu JF, Boschat AC, Sanquer S, glomerulosclerosis. N Engl J Med 365: 295–306, 2011 Menten B, Vergult S, De Rocker N, Airik M, Hermle T, Shril S, 23. Kaplan JM, Kim SH, North KN, Rennke H, Correia LA, Tong HQ, Widmeier E, Gee HY, Choi WI, Sadowski CE, Pabst WL, Warejko Mathis BJ, Rodrı´guez-Pe´rez JC, Allen PG, Beggs AH, Pollak MR: JK, Daga A, Basta T,Matejas V,Scharmann K, Kienast SD, Behnam Mutations in ACTN4, encoding alpha-actinin-4, cause familial B, Beeson B, Begtrup A, Bruce M, Ch’ng GS, Lin SP, Chang JH, focal segmental glomerulosclerosis. Nat Genet 24: 251–256, Chen CH, Cho MT, Gaffney PM, Gipson PE, Hsu CH, Kari JA, Ke 2000 YY, Kiraly-Borri C, Lai WM, Lemyre E, Littlejohn RO, Masri A, 24. Akilesh S, Koziell A, Shaw AS: Basic science meets clinical Moghtaderi M, Nakamura K, Ozaltin F, Praet M, Prasad C, Prytula medicine: Identification of a CD2AP-deficient patient. Kidney Int A, Roeder ER, Rump P, Schnur RE, Shiihara T, Sinha MD, Soliman 72: 1181–1183, 2007 NA, Soulami K, Sweetser DA, Tsai WH, Tsai JD, Topaloglu R, 25. Gee HY, Zhang F, Ashraf S, Kohl S, Sadowski CE, Vega-Warner V, Vester U, Viskochil DH, Vatanavicharn N, Waxler JL, Wierenga Zhou W, Lovric S, Fang H, Nettleton M, Zhu JY, Hoefele J, Weber KJ, Wolf MTF, Wong SN, Leidel SA, Truglio G, Dedon PC, Poduri LT,Podracka L, Boor A, Fehrenbach H, Innis JW, Washburn J, Levy A, Mane S, Lifton RP,Bouchard M, Kannu P,Chitayat D, Magen D, S, Lifton RP, Otto EA, Han Z, Hildebrandt F: KANK deficiency Callewaert B, van Tilbeurgh H, Zenker M, Antignac C, leads to podocyte dysfunction and nephrotic syndrome. J Clin Hildebrandt F: Mutations in KEOPS-complex genes cause ne- Invest 125: 2375–2384, 2015 phrotic syndrome with primary microcephaly. Nat Genet 49: 26. Buvall L, Wallentin H, Sieber J, Andreeva S, Choi HY, Mundel P, 1529–1538, 2017 Greka A: Synaptopodin is a coincidence detector of tyrosine 9. Rennke HG, Cotran RS, Venkatachalam MA: Role of molecular versus serine/threonine phosphorylation for the modulation of charge in glomerular permeability. Tracer studies with cationized Rho protein crosstalk in podocytes. J Am Soc Nephrol 28: 837– ferritins. J Cell Biol 67: 638–646, 1975 851, 2017 10. Patrakka J, Tryggvason K: Molecular make-up of the glomerular 27. Bierzynska A, Soderquest K, Dean P,Colby E, Rollason R, Jones C, filtration barrier. Biochem Biophys Res Commun 396: 164–169, Inward CD, McCarthy HJ, Simpson MA, Lord GM, Williams M, 2010 Welsh GI, Koziell AB, Saleem MA; NephroS; UK study of Ne- 11. St John PL, Abrahamson DR: Glomerular endothelial cells and phrotic Syndrome: MAGI2 mutations cause congenital nephrotic podocytes jointly synthesize laminin-1 and -11 chains. Kidney Int syndrome. J Am Soc Nephrol 28: 1614–1621, 2017 60: 1037–1046, 2001 28. Ashraf S, Kudo H, Rao J, KikuchiA, Widmeier E, Lawson JA, Tan W, 12. Lennon R, Byron A, Humphries JD, Randles MJ, Carisey A, Hermle T, Warejko JK, Shril S, Airik M, Jobst-Schwan T, Lovric S, Murphy S, Knight D, Brenchley PE, Zent R, Humphries MJ: Global Braun DA, Gee HY, Schapiro D, Majmundar AJ, Sadowski CE, analysis reveals the complexity of the human glomerular extra- Pabst WL, Daga A, van der Ven AT, Schmidt JM, Low BC, Gupta cellular matrix. J Am Soc Nephrol 25: 939–951, 2014 AB, Tripathi BK, Wong J, Campbell K, Metcalfe K, Schanze D, 13. Kestila¨ M, Lenkkeri U, Ma¨nnikko¨ M, Lamerdin J, McCready P, Niihori T, Kaito H, Nozu K, Tsukaguchi H, Tanaka R, Hamahira K, PutaalaH,RuotsalainenV,Morita T,NissinenM,HervaR,Kashtan Kobayashi Y, Takizawa T, Funayama R, Nakayama K, Aoki Y, CE, Peltonen L, Holmberg C, Olsen A, Tryggvason K: Positionally Kumagai N, Iijima K, FehrenbachH, Kari JA, El DesokyS, JalalahS, cloned gene for a novel glomerular protein--nephrin--is mutated Bogdanovic R, Stajic N, Zappel H, Rakhmetova A, Wassmer SR, in congenital nephrotic syndrome. Mol Cell 1: 575–582, 1998 Jungraithmayr T, Strehlau J, Kumar AS, Bagga A, Soliman NA, 14. Koziell A, Grech V, Hussain S, Lee G, Lenkkeri U, Tryggvason K, Mane SM, Kaufman L, Lowy DR, Jairajpuri MA, Lifton RP, Pei Y, Scambler P: Genotype/phenotype correlations of NPHS1 and Zenker M, Kure S, Hildebrandt F: Mutations in six genes NPHS2 mutations in nephrotic syndrome advocate a functional delineate a pathogenic pathway amenable to treatment. Nat inter-relationship in glomerular filtration. Hum Mol Genet 11: Commun 9: 1960, 2018 379–388, 2002 29. Lipska BS, Ranchin B, Iatropoulos P, Gellermann J, Melk A, 15. Solanki AK, Widmeier E, Arif E, Sharma S, Daga A, Srivastava P, Ozaltin F, Caridi G, Seeman T, Tory K, Jankauskiene A, Zurowska Kwon SH, Hugo H, Nakayama M, Mann N, Majmundar AJ, TanW, A, Szczepanska M, Wasilewska A, Harambat J, Trautmann A, Gee HY, Sadowski CE, Rinat C, Becker-Cohen R, Bergmann C, Peco-Antic A, Borzecka H, Moczulska A, Saeed B, Bogdanovic R, Rosen S, Somers M, Shril S, Huber TB, Mane S, Hildebrandt F, Kalyoncu M, Simkova E, Erdogan O, Vrljicak K, Teixeira A, Azocar Nihalani D: Mutations in KIRREL1, a slit diaphragm component, M, Schaefer F; PodoNet Consortium: Genotype-phenotype as- cause steroid-resistant nephrotic syndrome. Kidney Int 96: 883– sociations in WT1 glomerulopathy. Kidney Int 85: 1169–1178, 889, 2019 2014 16. Li J, Wang L, Wan L, Lin T,Zhao W,Cui H, Li H, Cao L, Wu J, Zhang 30. Vivante A, Chacham OS, Shril S, Schreiber R, Mane SM, Pode- T: Mutational spectrum and novel candidate genes in Chinese Shakked B, Soliman NA, Koneth I, Schiffer M, Anikster Y, children with sporadic steroid-resistant nephrotic syndrome. Hildebrandt F: Dominant PAX2 mutations may cause steroid- Pediatr Res 85: 816–821, 2019 resistant nephrotic syndrome and FSGS in children. Pediatr 17. Winn MP,Conlon PJ, Lynn KL, Farrington MK, Creazzo T,Hawkins Nephrol 34: 1607–1613, 2019 AF, Daskalakis N, Kwan SY, Ebersviller S, Burchette JL, Pericak- 31. Braun DA, Sadowski CE, Kohl S, Lovric S, Astrinidis SA, Pabst WL, Vance MA, Howell DN, Vance JM, Rosenberg PB: A mutation Gee HY, Ashraf S, Lawson JA, Shril S, Airik M, Tan W, Schapiro D, in the TRPC6 cation channel causes familial focal segmental Rao J, Choi WI, Hermle T, Kemper MJ, Pohl M, Ozaltin F, Konrad glomerulosclerosis. Science 308: 1801–1804, 2005 M, Bogdanovic R, Bu¨scher R, Helmchen U, Serdaroglu E, Lifton 18. Ilatovskaya DV, Staruschenko A: TRPC6 channel as an emerging RP, Antonin W, Hildebrandt F: Mutations in nuclear pore genes determinant of the podocyte injury susceptibility in kidney dis- NUP93, NUP205 and XPO5 cause steroid-resistant nephrotic eases. Am J Physiol Renal Physiol 309: F393–F397, 2015 syndrome. Nat Genet 48: 457–465, 2016 19. Barua M, Shieh E, Schlondorff J, Genovese G, Kaplan BS, Pollak 32. LemoineS, PanayeM,RabeyrinM,Errazuriz-CerdaE,Mousson de MR: Exome sequencing and in vitro studies identified podoca- Camaret B, Petiot P, Juillard L, Guebre-Egziabher F: Renal in- lyxin as a candidate gene for focal and segmental glomerulo- volvement in neuropathy, ataxia, retinitis pigmentosa (NARP) sclerosis. Kidney Int 85: 124–133, 2014 syndrome: A case report. Am J Kidney Dis 71: 754–757, 2018 10 CJASN

33. Bezdicka M, Dluholucky M, Cinek O, Zieg J: Successful main- 40. Salem RM, Todd JN, Sandholm N, Cole JB, Chen WM, Andrews D, tenance of partial remission in a child with COQ2 nephropathy by Pezzolesi MG, McKeigue PM, Hiraki LT, Qiu C, Nair V,Di Liao C, coenzyme Q10 treatment. Nephrology (Carlton) 25: 187–188, Cao JJ, Valo E, Onengut-Gumuscu S, Smiles AM, McGurnaghan 2020 SJ, Haukka JK, Harjutsalo V, Brennan EP, van Zuydam N, Ahlqvist 34. Genovese G, Friedman DJ, Ross MD, Lecordier L, Uzureau P, E, Doyle R, Ahluwalia TS, Lajer M, Hughes MF, Park J, Skupien J, Freedman BI, Bowden DW, Langefeld CD, Oleksyk TK, Uscinski Spiliopoulou A, Liu A, Menon R, Boustany-Kari CM, Kang HM, Knob AL, Bernhardy AJ, Hicks PJ, Nelson GW, Vanhollebeke B, Nelson RG, Klein R, Klein BE, Lee KE, Gao X, Mauer M, Maestroni Winkler CA, Kopp JB, Pays E, Pollak MR: Association of trypa- S, Caramori ML, de Boer IH, Miller RG, Guo J, Boright AP, nolytic ApoL1 variants with kidney disease in African Americans. Tregouet D, Gyorgy B, Snell-Bergeon JK, Maahs DM, Bull SB, Science 329: 841–845, 2010 Canty AJ, Palmer CNA, Stechemesser L, Paulweber B, Weitgasser 35. Okamoto K, Tokunaga K, Doi K, Fujita T, Suzuki H, Katoh T, R, Sokolovska J, Rovīte V, Pīrāgs V, Prakapiene E, Radzeviciene L, Watanabe T, Nishida N, Mabuchi A, Takahashi A, Kubo M, Verkauskiene R, Panduru NM, Groop LC, McCarthy MI, Gu HF, Maeda S, Nakamura Y, Noiri E: Common variation in GPC5 is Mo¨llsten A, Falhammar H, Brismar K, Martin F, Rossing P, associated with acquired nephrotic syndrome. Nat Genet 43: Costacou T, Zerbini G, Marre M, Hadjadj S, McKnight AJ, 459–463, 2011 Forsblom C, McKay G, Godson C, Maxwell AP, Kretzler M, 36. Funk SD, Lin MH, Miner JH: Alport syndrome and Pierson syn- Susztak K, Colhoun HM, Krolewski A, Paterson AD, Groop PH, drome: Diseases of the glomerular basement membrane. Matrix Rich SS, Hirschhorn JN, Florez JC; SUMMIT Consortium, DCCT/ Biol 71-72: 250–261, 2018 EDIC Research Group, GENIE Consortium: Genome-wide asso- 37. Braun DA, Warejko JK, Ashraf S, Tan W, Daga A, Schneider R, ciation study of diabetic kidney disease highlights biology in- Hermle T, Jobst-Schwan T, Widmeier E, Majmundar AJ, volved in glomerular basement membrane collagen. JAmSoc Nakayama M, Schapiro D, Rao J, Schmidt JM, Hoogstraten CA, Nephrol 30: 2000–2016, 2019 Hugo H, Bakkaloglu SA, Kari JA, El Desoky S, Daouk G, Mane S, 41. Steffensen LB, Rasmussen LM: A role for collagen type IV in Lifton RP, Shril S, Hildebrandt F: Genetic variants in the LAMA5 cardiovascular disease? Am J Physiol Heart Circ Physiol 315: gene in pediatric nephrotic syndrome. Nephrol Dial Transplant H610–H625, 2018 34: 485–493, 2019 42. Groopman EE, Marasa M, Cameron-Christie S, Petrovski S, 38. Jeanne M, Labelle-Dumais C, Jorgensen J, Kauffman WB, Aggarwal VS, Milo-Rasouly H, Li Y, Zhang J, Nestor J, ManciniGM,FavorJ,ValantV,GreenbergSM,RosandJ,Gould Krithivasan P, Lam WY, Mitrotti A, Piva S, Kil BH, Chatterjee D, DB: COL4A2 mutations impair COL4A1 and COL4A2 secre- Reingold R, Bradbury D, DiVecchia M, Snyder H, Mu X, Mehl K, tion and cause hemorrhagic stroke. Am J Hum Genet 90: 91– Balderes O, Fasel DA, Weng C, Radhakrishnan J, Canetta P, 101, 2012 Appel GB, Bomback AS, Ahn W,Uy NS, Alam S, CohenDJ,Crew 39. Malik R, Chauhan G, Traylor M, Sargurupremraj M, Okada Y, RJ, Dube GK, Rao MK, Kamalakaran S, Copeland B, Ren Z, Mishra A, Rutten-Jacobs L, Giese AK, van der Laan SW, Bridgers J, Malone CD, Mebane CM, Dagaonkar N, Fellstro¨m Gretarsdottir S, Anderson CD, Chong M, Adams HHH, Ago T, BC, Haefliger C, Mohan S, Sanna-Cherchi S, Kiryluk K, Fleckner Almgren P, Amouyel P, Ay H, Bartz TM, Benavente OR, Bevan S, J, March R, Platt A, Goldstein DB, Gharavi AG: Diagnostic utility Boncoraglio GB, Brown RD Jr., Butterworth AS, Carrera C, Carty of exome sequencing for kidney disease. NEnglJMed380: 142– CL, Chasman DI, Chen WM, Cole JW, Correa A, Cotlarciuc I, 151, 2019 Cruchaga C, Danesh J, de Bakker PIW, DeStefano AL, den Hoed 43. Lennon R, Randles MJ, Humphries MJ: The importance of po- M, Duan Q, Engelter ST, Falcone GJ, Gottesman RF, Grewal RP, docyte adhesion for a healthy glomerulus. Front Endocrinol Gudnason V, Gustafsson S, Haessler J, Harris TB, Hassan A, (Lausanne) 5: 160, 2014 Havulinna AS, Heckbert SR, Holliday EG, Howard G, Hsu FC, 44. Has C, Sparta` G, Kiritsi D, Weibel L, Moeller A, Vega-Warner V, Hyacinth HI, Ikram MA, Ingelsson E, Irvin MR, Jian X, Jime´nez- Waters A, He Y, Anikster Y, Esser P, Straub BK, Hausser I, Conde J, Johnson JA, Jukema JW, Kanai M, Keene KL, Kissela BM, Bockenhauer D, Dekel B, Hildebrandt F, Bruckner-Tuderman L, Kleindorfer DO, Kooperberg C, Kubo M, Lange LA, Langefeld CD, Laube GF: Integrin a3 mutations with kidney, lung, and skin Langenberg C, Launer LJ, Lee JM, Lemmens R, Leys D, Lewis CM, disease. N Engl J Med 366: 1508–1514, 2012 Lin WY, Lindgren AG, Lorentzen E, Magnusson PK, Maguire J, 45. KambhamN, Tanji N,SeigleRL, MarkowitzGS,PulkkinenL,Uitto Manichaikul A, McArdle PF,Meschia JF, Mitchell BD, Mosley TH, J, D’Agati VD: Congenital focal segmental glomerulosclerosis Nalls MA, Ninomiya T, O’Donnell MJ, Psaty BM, Pulit SL, associated with beta4 integrin mutation and epidermolysis bul- Rannikma¨e K, Reiner AP,Rexrode KM, Rice K, RichSS, Ridker PM, losa. Am J Kidney Dis 36: 190–196, 2000 Rost NS, Rothwell PM, Rotter JI, Rundek T, Sacco RL, Sakaue S, 46. Okamoto K, Honda K, Doi K, Ishizu T, Katagiri D, Wada T, Tomita Sale MM, Salomaa V, Sapkota BR, Schmidt R, Schmidt CO, K, Ohtake T, Kaneko T, Kobayashi S, Nangaku M, Tokunaga K, Schminke U, Sharma P, Slowik A, Sudlow CLM, Tanislav C, Noiri E: Glypican-5 increases susceptibility to nephrotic damage Tatlisumak T, Taylor KD, Thijs VNS, Thorleifsson G, in diabetic kidney. Am J Pathol 185: 1889–1898, 2015 Thorsteinsdottir U, Tiedt S, Trompet S, Tzourio C, van Duijn CM, 47. Naudin C, Smith B, Bond DR, Dun MD, Scott RJ, Ashman LK, Walters M, Wareham NJ, Wassertheil-Smoller S, Wilson JG, Weidenhofer J, Roselli S: Characterization of the early molecular Wiggins KL, Yang Q, Yusuf S, Bis JC, Pastinen T, Ruusalepp A, changes in the glomeruli of Cd151 -/- mice highlights induction of Schadt EE, Koplev S, Bjo¨rkegren JLM, Codoni V,Civelek M, Smith mindin and MMP-10. Sci Rep 7: 15987, 2017 NL, Tre´goue¨t DA, Christophersen IE, Roselli C, Lubitz SA, Ellinor 48. Karamatic Crew V, Burton N, Kagan A, Green CA, Levene C, PT, Tai ES, Kooner JS, Kato N, He J, van der Harst P, Elliott P, Flinter F,BradyRL, Daniels G, Anstee DJ: CD151, the first member Chambers JC, Takeuchi F,Johnson AD, Sanghera DK, Melander O, of the tetraspanin (TM4) superfamily detected on erythrocytes, is Jern C, Strbian D, Fernandez-Cadenas I, Longstreth WT Jr., Rolfs A, essential for the correct assembly of human basement membranes Hata J, Woo D, Rosand J, Pare G, Hopewell JC, Saleheen D, in kidney and skin. Blood 104: 2217–2223, 2004 Stefansson K, Worrall BB, Kittner SJ, Seshadri S, Fornage M, 49. Bresin E, Rurali E, Caprioli J, Sanchez-Corral P, Fremeaux-Bacchi Markus HS, Howson JMM, Kamatani Y, Debette S, Dichgans M; V, Rodriguez de Cordoba S, Pinto S, Goodship TH, Alberti M, AFGen Consortium; Cohorts for Heart and Aging Research in Ribes D, Valoti E, Remuzzi G, Noris M; European Working Party Genomic Epidemiology (CHARGE) Consortium; International on Complement Genetics in Renal Diseases: Combined com- Genomics of (iGEN-BP) Consortium; INVENT plement gene mutations in atypical hemolytic uremic syndrome Consortium; STARNET; BioBank Japan Cooperative Hospital influence clinical phenotype. J Am Soc Nephrol 24: 475–486, Group; COMPASS Consortium; EPIC-CVD Consortium; EPIC- 2013 InterAct Consortium; International Stroke Genetics Consortium 50. Lemaire M, Fre´meaux-Bacchi V,Schaefer F, Choi M, Tang WH, Le (ISGC); METASTROKE Consortium; Neurology Working Group of Quintrec M, Fakhouri F, Taque S, Nobili F, Martinez F, Ji W, the CHARGE Consortium; NINDS Stroke Genetics Network Overton JD, Mane SM, Nu¨rnberg G, Altmu¨ller J, Thiele H, Morin (SiGN); UK Young Lacunar DNA Study; MEGASTROKE Consor- D, Deschenes G, Baudouin V, Llanas B, Collard L, Majid MA, tium: Multiancestry genome-wide association study of 520,000 Simkova E, Nu¨rnberg P, Rioux-Leclerc N, Moeckel GW, Gubler subjects identifies 32 loci associated with stroke and stroke MC, Hwa J, Loirat C, Lifton RP: Recessive mutations in DGKE subtypes [published correction appears in Nat Genet 51: 1192– cause atypical hemolytic-uremic syndrome. Nat Genet 45: 531– 1193, 2019]. Nat Genet 50: 524–537, 2018 536, 2013 CJASN 15: ccc–ccc, December, 2020 Glomerular Genetics, Li et al. 11

51. Challis RC, Ring T, Xu Y, Wong EK, Flossmann O, Roberts IS, current molecular and genetic advances. Pediatr Nephrol 33: Ahmed S, Wetherall M, Salkus G, Brocklebank V,Fester J, Strain L, 2027–2035, 2018 Wilson V, Wood KM, Marchbank KJ, Santibanez-Koref M, 56. Feltran LS, Varela P, Silva ED, Veronez CL, Franco MC, Filho AP, Goodship TH, Kavanagh D: Thrombotic microangiopathy in in- Camargo MF, Koch Nogueira PC, Pesquero JB: Targeted next- verted formin 2-mediated renal disease. J Am Soc Nephrol 28: generation sequencing in Brazilian children with nephrotic 1084–1091, 2017 syndrome submitted to renal transplant. Transplantation 101: 52. Gast C, Pengelly RJ, Lyon M, Bunyan DJ, Seaby EG, Graham N, 2905–2912, 2017 Venkat-Raman G, Ennis S: Collagen (COL4A) mutations are the 57. Lin X, Suh JH, Go G, Miner JH: Feasibility of repairing glomerular most frequent mutations underlying adult focal segmental glo- basement membrane defects in Alport syndrome. JAmSoc merulosclerosis. Nephrol Dial Transplant 31: 961–970, 2016 Nephrol 25: 687–692, 2014 53. Yao T, Udwan K, John R, Rana A, Haghighi A, Xu L, Hack S, Reich 58. Heidet L, Borza DB, Jouin M, Sich M, Mattei MG, Sado Y,Hudson HN, Hladunewich MA, Cattran DC, Paterson AD, Pei Y, Barua M: BG, Hastie N, Antignac C, Gubler MC: A human-mouse chimera Integration of genetic testing and pathology for the diagnosis of of the alpha3alpha4alpha5(IV) collagen protomer rescues the adults with FSGS. Clin J Am Soc Nephrol 14: 213–223, 2019 renal phenotype in Col4a3-/- Alport mice. Am J Pathol 163: 1633– 54. Gross O, Friede T,Hilgers R, Go¨rlitz A, Gave´nis K, Ahmed R, Du¨rr 1644, 2003 U: Safety and efficacy of the ACE-inhibitor ramipril in alport 59. Yu G, Wang LG, Han Y, He QY: clusterProfiler: An R package for syndrome: The double-blind, randomized, placebo-controlled, comparing biological themes among gene clusters. OMICS 16: multicenter phase III EARLY PRO-TECT Alport trial in pediatric 284–287, 2012 patients. ISRN Pediatr 2012: 436046, 2012 55. Bierzynska A, Saleem MA: Deriving and understanding the risk of Published online ahead of print. Publication date available at post-transplant recurrence of nephrotic syndrome in the light of www.cjasn.org.