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      Mutations in the INF2 gene account for a significant proportion of familial but not sporadic focal and segmental glomerulosclerosis

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          Abstract

          Mutations in the inverted formin 2 gene ( INF2) have recently been identified as the most common cause of autosomal dominant focal and segmental glomerulosclerosis (FSGS). In order to quantify the contribution of various genes contributing to FSGS, we sequenced INF2 where all mutations have previously been described (exons 2 to 5) in a total of 215 probands and 281 sporadic individuals with FSGS, along with other known genes accounting for autosomal dominant FSGS ( ACTN4, TRPC6 and CD2AP) in 213 probands. Variants were classified as disease-causing if they altered the amino acid sequence, were not found in control samples, and in families segregated with disease. Mutations in INF2 were found in a total of 20 of the 215 families (including those previously reported) in our cohort of autosomal dominant familial nephrotic syndrome or FSGS, thereby explaining disease in 9 percent. INF2 mutations were found in 2 of 281 individuals with sporadic FSGS. In contrast, ACTN4 and TRPC6-related disease accounted for 3 and 2 percent of our familial cohort, respectively. INF2-related disease showed variable penetrance, with onset of disease ranging widely from childhood to adulthood and commonly leading to ESRD in the third and fourth decade of life. Thus, mutations in INF2 are more common, although still minor, monogenic cause of familial FSGS when compared to other known autosomal dominant genes associated with FSGS.

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          Most cited references26

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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

                Journal
                0323470
                5428
                Kidney Int
                Kidney Int.
                Kidney international
                0085-2538
                1523-1755
                9 October 2012
                26 September 2012
                February 2013
                01 August 2013
                : 83
                : 2
                : 316-322
                Affiliations
                [1 ]Division of Nephrology, Dept. of Medicine, Beth Israel Deaconess Medical Center, Boston, MA, United States
                [2 ]Division of Nephrology, Dept. of Medicine, Boston Children’s Hospital, Boston, MA, United States
                Author notes
                Correspondence to: Martin Pollak, MD, Chief, Division of Nephrology, Beth Israel Deaconess Medical Center, Professor of Medicine, Harvard Medical School, 99 Brookline Ave, Boston, MA 02215, TEL 617-667-0461, FAX 617-667-0495, mpollak@ 123456bidmc.harvard.edu
                [+]

                These authors contributed equally to this work

                Article
                NIHMS403964
                10.1038/ki.2012.349
                3647680
                23014460
                98e21975-a9df-4d64-a680-920648a11aea
                History
                Funding
                Funded by: National Institute of Diabetes and Digestive and Kidney Diseases : NIDDK
                Award ID: R01 DK054931 || DK
                Categories
                Article

                Nephrology
                familial fsgs,fsgs,inf2,mutations,nephrotic syndrome,sporadic cases
                Nephrology
                familial fsgs, fsgs, inf2, mutations, nephrotic syndrome, sporadic cases

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