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      Familial forms of nephrotic syndrome

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          Abstract

          The recent discovery of genes involved in familial forms of nephrotic syndrome represents a break-through in nephrology. To date, 15 genes have been characterized and several new loci have been identified, with a potential for discovery of new genes. Overall, these genes account for a large fraction of familial forms of nephrotic syndrome, but they can also be recognized in 10–20% of sporadic cases. These advances increase diagnostic and therapeutic potentials, but also add higher complexity to the scenario, requiring clear definitions of clinical, histopathological and molecular signatures. In general, genetic forms of nephrotic syndrome are resistant to common therapeutic approaches (that include steroids and calcineurin inhibitors) but, in a few cases, drug response or spontaneous remission suggest a complex pathogenesis. Finally, syndromic variants can be recognized on the basis of the associated extra-renal manifestations. In this educational review, clinical, histological and molecular aspects of various forms of familial nephrotic syndrome have been reviewed in an attempt to define a rational diagnostic approach. The proposed model focuses on practical and economic issues, taking into consideration the impossibility of using genetic testing as starting diagnostic tool. The final objective of this review is to outline a diagnostic flow-chart for clinicians and geneticists and to generate a rational scheme for molecular testing.

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          NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome.

          Familial idiopathic nephrotic syndromes represent a heterogeneous group of kidney disorders, and include autosomal recessive steroid-resistant nephrotic syndrome, which is characterized by early childhood onset of proteinuria, rapid progression to end-stage renal disease and focal segmental glomerulosclerosis. A causative gene for this disease, NPHS2, was mapped to 1q25-31 and we report here its identification by positional cloning. NPHS2 is almost exclusively expressed in the podocytes of fetal and mature kidney glomeruli, and encodes a new integral membrane protein, podocin, belonging to the stomatin protein family. We found ten different NPHS2 mutations, comprising nonsense, frameshift and missense mutations, to segregate with the disease, demonstrating a crucial role for podocin in the function of the glomerular filtration barrier.
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            Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.

            Focal and segmental glomerulosclerosis (FSGS) is a common, non-specific renal lesion. Although it is often secondary to other disorders, including HIV infection, obesity, hypertension and diabetes, FSGS also appears as an isolated, idiopathic condition. FSGS is characterized by increased urinary protein excretion and decreasing kidney function. Often, renal insufficiency in affected patients progresses to end-stage renal failure, a highly morbid state requiring either dialysis therapy or kidney transplantation. Here we present evidence implicating mutations in the gene encoding alpha-actinin-4 (ACTN4; ref. 2), an actin-filament crosslinking protein, as the cause of disease in three families with an autosomal dominant form of FSGS. In vitro, mutant alpha-actinin-4 binds filamentous actin (F-actin) more strongly than does wild-type alpha-actinin-4. Regulation of the actin cytoskeleton of glomerular podocytes may be altered in this group of patients. Our results have implications for understanding the role of the cytoskeleton in the pathophysiology of kidney disease and may lead to a better understanding of the genetic basis of susceptibility to kidney damage.
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              TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.

              Progressive kidney failure is a genetically and clinically heterogeneous group of disorders. Podocyte foot processes and the interposed glomerular slit diaphragm are essential components of the permeability barrier in the kidney. Mutations in genes encoding structural proteins of the podocyte lead to the development of proteinuria, resulting in progressive kidney failure and focal segmental glomerulosclerosis. Here, we show that the canonical transient receptor potential 6 (TRPC6) ion channel is expressed in podocytes and is a component of the glomerular slit diaphragm. We identified five families with autosomal dominant focal segmental glomerulosclerosis in which disease segregated with mutations in the gene TRPC6 on chromosome 11q. Two of the TRPC6 mutants had increased current amplitudes. These data show that TRPC6 channel activity at the slit diaphragm is essential for proper regulation of podocyte structure and function.
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                Author and article information

                Contributors
                +39-010-380742 , +39-010-395214 , labnefro@ospedale-gaslini.ge.it
                Journal
                Pediatr Nephrol
                Pediatr. Nephrol
                Pediatric Nephrology (Berlin, Germany)
                Springer Berlin Heidelberg (Berlin/Heidelberg )
                0931-041X
                1432-198X
                1 February 2010
                1 February 2010
                2010
                : 25
                : 2
                : 241-252
                Affiliations
                [1 ]GRID grid.419504.d, ISNI 0000000417600109, Laboratory on Physiopathology of Uremia, , G. Gaslini Children Hospital, ; Genoa, Italy
                [2 ]GRID grid.21729.3f, ISNI 0000000419368729, Department of Medicine, Division of Nephrology, , Columbia University College of Physicians and Surgeons, ; New York, NY USA
                [3 ]GRID grid.419504.d, ISNI 0000000417600109, Division of Nephrology, Dialysis and Transplantation, , G. Gaslini Children Hospital, ; Largo G. Gaslini, 5, 16148 Genova, Italy
                Article
                1051
                10.1007/s00467-008-1051-3
                6904408
                19066979
                1f933ebe-d92b-406b-9ca0-c911a6ac4d3a
                © IPNA 2008

                This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 4 June 2008
                : 8 October 2008
                : 8 October 2008
                Categories
                Educational Review
                Custom metadata
                © IPNA 2010

                Nephrology
                molecular genetics,nephrin,nephrotic syndrome,podocin,podocytes
                Nephrology
                molecular genetics, nephrin, nephrotic syndrome, podocin, podocytes

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