A novel mutation, outside of the candidate region for diagnosis, in the inverted formin 2 gene can cause focal segmental glomerulosclerosis
2012; Elsevier BV; Volume: 83; Issue: 1 Linguagem: Inglês
10.1038/ki.2012.325
ISSN1523-1755
AutoresMaría Sánchez‐Ares, Marina Garcia-Vidal, Espinosa-Estevez Antucho, Pardo Julio, Vazquez-Martul Eduardo, Xosé M. Lens, Miguel A. García-González,
Tópico(s)Celiac Disease Research and Management
ResumoFocal and segmental glomerulosclerosis (FSGS) is a histological pattern that has several etiologies, including genetics. The autosomal dominant form of FSGS is a heterogenic disease caused by mutations within three known genes: α-actinin 4 (ACTN4), canonical transient receptor potential 6 (TRPC6), and the inverted formin 2 (INF2) gene. More recently, INF2 mutations have also been attributed to Charcot–Marie–Tooth neuropathy associated with FSGS. Here we performed direct sequencing, histological characterization, and functional studies in a cohort of families with autosomal dominant FSGS. We detected a novel mutation in exon 6 of the INF2 gene outside of the exon 2–4 candidate region used for rapid diagnosis of autosomal dominant FSGS. This new mutation is predicted to alter a highly conserved amino-acid residue within the 17th α-helix of the diaphanous inhibitory domain of the protein. A long-term follow-up of this family indicated that all patients were diagnosed in adulthood, as opposed to early childhood, and progression to end-stage renal disease was at different times without clinical or electrodiagnostic evidence of neuropathy. Thus, this novel mutation in INF2 linked to nonsyndromic FSGS indicates the necessity for full gene sequencing if no mutation is found in the current rapid-screen region of the gene. Focal and segmental glomerulosclerosis (FSGS) is a histological pattern that has several etiologies, including genetics. The autosomal dominant form of FSGS is a heterogenic disease caused by mutations within three known genes: α-actinin 4 (ACTN4), canonical transient receptor potential 6 (TRPC6), and the inverted formin 2 (INF2) gene. More recently, INF2 mutations have also been attributed to Charcot–Marie–Tooth neuropathy associated with FSGS. Here we performed direct sequencing, histological characterization, and functional studies in a cohort of families with autosomal dominant FSGS. We detected a novel mutation in exon 6 of the INF2 gene outside of the exon 2–4 candidate region used for rapid diagnosis of autosomal dominant FSGS. This new mutation is predicted to alter a highly conserved amino-acid residue within the 17th α-helix of the diaphanous inhibitory domain of the protein. A long-term follow-up of this family indicated that all patients were diagnosed in adulthood, as opposed to early childhood, and progression to end-stage renal disease was at different times without clinical or electrodiagnostic evidence of neuropathy. Thus, this novel mutation in INF2 linked to nonsyndromic FSGS indicates the necessity for full gene sequencing if no mutation is found in the current rapid-screen region of the gene. Focal and segmental glomerulosclerosis (FSGS) is a histological pattern with different etiologies: primary (idiopathic) and secondary (i.e., those forms with known etiology).1.D'Agati V.D. The spectrum of focal segmental glomerulosclerosis: new insights.Curr Opin Nephrol Hypertens. 2008; 17: 271-281Crossref PubMed Scopus (117) Google Scholar The clinical pattern is characterized by heavy proteinuria, nephrotic syndrome, and the progressive loss of renal function, probably resulting in end-stage renal disease (ESRD) and renal replacement therapy. There has been a significant effort to classify both the etiology and pathology of FSGS; however, given its variable manifestations, physicians and researchers continue to struggle to understand the molecular mechanisms of the disease.1.D'Agati V.D. The spectrum of focal segmental glomerulosclerosis: new insights.Curr Opin Nephrol Hypertens. 2008; 17: 271-281Crossref PubMed Scopus (117) Google Scholar, 2.Barisoni L. Schnaper H.W. Kopp J.B. A proposed taxonomy for the podocytopathies: a reassessment of the primary nephrotic diseases.Clin J Am Soc Nephrol. 2007; 2: 529-542Crossref PubMed Scopus (201) Google Scholar, 3.Benoit G. Machuca E. Antignac C. Hereditary nephrotic syndrome: a systematic approach for genetic testing and a review of associated podocyte gene mutations.Pediatr Nephrol. 2010; 25: 1621-1632Crossref PubMed Scopus (137) Google Scholar, 4.Pollak M.R. Focal segmental glomerulosclerosis: recent advances.Curr Opin Nephrol Hypertens. 2008; 17: 138-142Crossref PubMed Scopus (34) Google Scholar Familial forms of FSGS account for up to 18% of all cases,5.Weins A. Kenlan P. Herbert S. et al.Mutational and biological analysis of alpha-actinin-4 in focal segmental glomerulosclerosis.J Am Soc Nephrol. 2005; 16: 3694-3701Crossref PubMed Scopus (141) Google Scholar and the vast majority of these cases present with early childhood onset, whereas adult onset is very uncommon. The clinical spectrum is strongly influenced by the type of inheritance pattern. Indeed, autosomal recessive FSGS usually manifests as a severe phenotype with an early onset in neonates and young children, whereas the autosomal dominant FSGS (AD-FSGS) form is generally associated with a juvenile or adult onset. Several genes have been implicated with both autosomal recessive FSGS (NPHS1-encoding nephrin6.Kestila M. Lenkkeri U. Mannikko M. et al.Positionally cloned gene for a novel glomerular protein—nephrin—is mutated in congenital nephrotic syndrome.Mol Cell. 1998; 1: 575-582Abstract Full Text Full Text PDF PubMed Scopus (1563) Google Scholar, NPHS2-encoding podocin,7.Boute N. Gribouval O. Roselli S. et al.NPHS2, encoding the glomerular protein podocin, is mutated in autosomal recessive steroid-resistant nephrotic syndrome.Nat Genet. 2000; 24: 349-354Crossref PubMed Scopus (1198) Google Scholar and PLCE1-encoding phosphoinositide-specific phospholipase C epsilon-18.Hinkes B. Wiggins R.C. Gbadegesin R. et al.Positional cloning uncovers mutations in PLCE1 responsible for a nephrotic syndrome variant that may be reversible.Nat Genet. 2006; 38: 1397-1405Crossref PubMed Scopus (450) Google Scholar) and AD-FSGS (ACTN4-encoding alpha-actinin 49.Kaplan J.M. Kim S.H. North K.N. et al.Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.Nat Genet. 2000; 24: 251-256Crossref PubMed Scopus (1040) Google Scholar and TRPC6-encoding canonical transient receptor potential 610.Reiser J. Polu K.R. Moller C.C. et al.TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.Nat Genet. 2005; 37: 739-744Crossref PubMed Scopus (680) Google Scholar,11.Winn M.P. Conlon P.J. Lynn K.L. et al.A mutation in the TRPC6 cation channel causes familial focal segmental glomerulosclerosis.Science. 2005; 308: 1801-1804Crossref PubMed Scopus (888) Google Scholar). Recently, Brown et al.12.Brown E.J. Schlondorff J.S. Becker D.J. et al.Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis.Nat Genet. 2010; 42: 72-76Crossref PubMed Scopus (340) Google Scholar described a new locus for AD-FSGS on chromosome 14q32 that includes the inverted formin 2 (INF2) gene. To date, approximately 15% of screened AD-FSGS cases (n=194) have been linked to mutations in INF2.12.Brown E.J. Schlondorff J.S. Becker D.J. et al.Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis.Nat Genet. 2010; 42: 72-76Crossref PubMed Scopus (340) Google Scholar, 13.Lee H.K. Han K.H. Jung Y.H. et al.Variable renal phenotype in a family with an INF2 mutation.Pediatr Nephrol. 2010; 26: 73-76Crossref PubMed Scopus (27) Google Scholar, 14.Boyer O. Benoit G. Gribouval O. et al.Mutations in INF2 are a major cause of autosomal dominant focal segmental glomerulosclerosis.J Am Soc Nephrol. 2011; 22: 239-245Crossref PubMed Scopus (129) Google Scholar, 15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar More recently, Boyer et al.16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar discovered that mutations in INF2 are also responsible for Charcot–Marie–Tooth (CMT) neuropathy associated with FSGS. In both cases, mutations associated with the syndromic and nonsyndromic form of the disease are clustered in exons 2 to 4 of INF2, which encode the diaphanous inhibitory domain (DID). However, most syndromic mutations are localized between two putative DID-binding pockets coded by the 3′ end of exon 2 and 3, affecting DID function more severely than mutations related to the nonsyndromic disease. Exons 2–4 has been suggested as a rapid screening method for the diagnosis of both AD-FSGS15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar and CMT with glomerulopathy.16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar The DID domain allows INF2 to accelerate the polymerization and depolymerization of actin filaments and regulate specialized routes of protein targeting to the plasma membrane by forming protein complexes with Rho-GTPases, CDC42, and myelin and lymphocyte (MAL) protein, or MAL2 in podocytes and Schwann cells.16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar, 17.Chhabra E.S. Higgs H.N. INF2 Is a WASP homology 2 motif-containing formin that severs actin filaments and accelerates both polymerization and depolymerization.J Biol Chem. 2006; 281: 26754-26767Crossref PubMed Scopus (151) Google Scholar, 18.Lammers M. Meyer S. Kuhlmann D. et al.Specificity of interactions between mDia isoforms and Rho proteins.J Biol Chem. 2008; 283: 35236-35246Crossref PubMed Scopus (89) Google Scholar The main objective of this study is to conduct correlation studies in our cohort of Spanish AD-FSGS families. Although very little is known about INF2, the information provided by the mutational analysis in patients will help us improve our understanding of its functions and the pathogenesis of FSGS and CMT. We performed mutational analysis for AD-FSGS genes in five families (19 affected and 108 unaffected individuals) with a presumably autosomal dominant mode of inheritance of FSGS with two or more affected individuals in at least two generations.15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar Patients were classified following the inclusion criteria described below (Materials and Methods section). The age of diagnosis, maximum proteinuria levels, the presence of microhematuria and/or arterial hypertension, age at ESRD, and recurrence after transplant of affected individuals are presented in Supplementary Table S1 online. Initial mutational analyses for ACTN4 and TRPC6 were negative (sequence variants are shown in Supplementary Table S2 online). After the discovery by Brown et al.12.Brown E.J. Schlondorff J.S. Becker D.J. et al.Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis.Nat Genet. 2010; 42: 72-76Crossref PubMed Scopus (340) Google Scholar that INF2 mutations cause FSGS, we expanded our mutational analysis to this gene and identified a novel point mutation (L245P) in the CHUS_FSGS-2 family (see Supplementary Table S2 online for INF2 sequence variants). Download .doc (.18 MB) Help with doc files Supplementary Table S1 to S3 The proband of CHUS_FSGS-2 is a 21-year-old man (Figure 1 and Table 1, III:2) who had elevated blood urea, proteinuria in a nephrotic range, and microhematuria in a health maintenance visit; therefore, he was immediately referred to our hospital. Upon admission, he had an elevated blood pressure (170/110mmHg) with normal cardiothoracic and abdominal examinations. Blood tests showed abnormal levels of hemoglobin (10.7g/dl), total plasma protein content (5.7g/dl), albumin (3.3g/dl), urea (125mg/dl), creatinine (4.5mg/dl), cholesterol (438mg/dl), and triglycerides (253mg/dl). Urinalysis confirmed a nephrotic-range proteinuria (7g/l) and microhematuria. Renal ultrasound showed small kidneys (left, 80mm; right, 85mm) with hyperechogenic parenchyma.Table 1Phenotypes of affected patients in the CHUS_FSGS-2 familyII:3III:2III:3Age at diagnosis (years)262128Maximal proteinuria (g/l)N/A77.8MicrohematuriaN/AYesNoArterial hypertensionN/AYesYesSteroid responseUntreatedUntreatedResistantCyclosporine responseUntreatedUntreatedUnresponsiveAge at ESRD (years)262235Renal transplantationNoYesYesRecurrence post transplantation—Not after 13 yearsNot after 6 yearsAbbreviations: ESRD, end-stage renal disease; N/A, not available. Open table in a new tab Abbreviations: ESRD, end-stage renal disease; N/A, not available. On light microscopy, renal biopsy revealed FSGS with advanced glomerular damage. Several glomeruli already showed solidification of the entire tuft or global sclerosis. Severe tubulointerstitial injuries were also observed in areas of advanced tubular atrophy and interstitial fibrosis. Electron microscopy revealed extensive foot process effacement of podocytes without electron-dense deposits (data not shown). We continued to follow-up the patient and observed that his renal function progressively declined. Within 6 months, he progressed to ESRD and underwent hemodialysis. A cadaveric renal transplant was performed at the age of 23. After a follow-up of 13 years post renal transplant (at the age of 36), there were no signs of FSGS recurrence. Given that INF2 mutations can be associated with CMT,16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar a complete clinical neurological evaluation was performed. The patient did not complain of numbness or weakness. Neurological examinations did not show signs of peripheral neuropathy, and pes cavus was not found. In addition to this, results of motor and sensory nerve conduction studies in the upper and lower limbs were normal. Further analysis of the proband's family history revealed that his father and his brother (Figure 1, II:3 and III:3, respectively) also suffered from renal disease. The father was diagnosed at the age of 26 with advanced-stage renal failure, in addition to having symptoms of severe fatigue, polyuria, and high urea levels. Emergency hemodialysis was performed, but he died a few days later from technical complications. Clinical records for the proband's brother (III:3) started at the age of 28 when elevated proteinuria was detected. He was referred to our hospital where a physical examination showed exclusively high blood pressure (155/80mmHg). Blood tests revealed hypercholesterolemia (293mg/dl) and normal renal function (urea and creatinine levels of 31 and 1.2mg/dl, respectively). A urinalysis showed normal urine sediment with elevated levels of proteinuria (7.8g/l); the renal ultrasound was normal, and subsequently a renal biopsy was performed. Light microscopic findings for patient III:3 demonstrated glomerular lesions characteristic of FSGS. Electron microscopy exhibited diffuse foot process effacement in all capillary loops. We also observed nonspecific ultrastructural changes in the mesangium and basal lamina, with irregular thickness of the subendothelial space, incipient widening, and duplication of the basal lamina. In some glomerular areas, a few granular and round particles were found in the mesangium and basal lamina (Figure 2). Immunofluorescent microscopy using glomerular markers detected focal and segmental deposits of C3 and mesangial IgM, with negative results for other immunoglobulins and complement fractions (data not shown). Initially, a prolonged oral steroid treatment (1.5mg/kg/day for 6 months) had no effect on his proteinuria, and his disease was considered steroid resistant. Subsequently, patient III:3 was treated with cyclosporine A (starting dose: 3mg/kg bw/day, maintaining the trough level between 80 and 100ng/ml) for 18 months; however, this treatment was also ineffective in reducing proteinuria levels. In addition, patient III:3 was treated with simvastatin for hypercholesterolemia and lisinopril for arterial hypertension. Lisinopril did not have an antiproteinuric effect. The patient's renal function progressively decreased, reaching ESRD 7 years after renal biopsy, and the patient started hemodialysis at the age of 35. Two years later, patient III:3 received a cadaveric renal transplant, and after 6 years of follow-up, his renal function remains normal with no signs of proteinuria. Neurological examinations and sensory and motor nerve conduction studies in upper and lower limbs were normal, without evidence of peripheral neuropathy. From the AD-FSGS families in our cohort, we only found the disease associated with the novel INF2 variant in one family (CHUS_FSGS-2). This mutation consists of a thymine-to-cytosine nucleotide substitution at exon 6 (c.734T>C), which is predicted to substitute a leucine residue for a proline residue in the INF2 protein (p.L245P, Figure 3a). To ensure segregation with AD-FSGS, we confirmed that the L245P mutation was carried only by the affected family members and was not present in unaffected members (II:2, II:4, II:6, II:8, II:11, and III:10). In addition, this mutation was not identified in our control chromosomes or in public single-nucleotide polymorphism databases and the 1000 Genome Project. Supplementary Table S2 online shows a number of novel and previously described polymorphisms detected in our cohort of AD-FSGS families. The mutation c.846T>C is located within the DID domain of INF2 (Figure 3b) and is an evolutionarily highly conserved residue between humans, chimpanzees, mice, and zebrafish INF2; human diaphanous-related formin 1; and mouse diaphanous-related formin 1 (mDia1) (Figure 3c). In addition, PolyPhen-2 predicts the pathogenicity of L245P to be 'Probably Damaging,' with a score of 0.979 (sensitivity: 0.67; specificity: 0.94),19.Adzhubei I.A. Schmidt S. Peshkin L. et al.A method and server for predicting damaging missense mutations.Nat Methods. 2010; 7: 248-249Crossref PubMed Scopus (9288) Google Scholar and Sorting Tolerant From Intolerant (SIFT) software found this mutation to be harmful, with a score of 0.03.20.Kumar P. Henikoff S. Ng P.C. Predicting the effects of coding non-synonymous variants on protein function using the SIFT algorithm.Nat Protoc. 2009; 4: 1073-1081Crossref PubMed Scopus (5006) Google Scholar Structural analysis predicts that the L245P mutation alters the architecture of the 17th α-helix (amino acids 239–264) of the DID domain by causing a turn point and forcing a bend of approximately 30° in the helix axis of this domain (Figure 4). AD-FSGS is an uncommon form of familial FSGS that usually affects juvenile and adult patients, presenting as late-onset proteinuria and often leading to ESRD. Mutations in ACTN4 and TRPC6 have been associated with 7% of all screened cases of AD-FSGS.5.Weins A. Kenlan P. Herbert S. et al.Mutational and biological analysis of alpha-actinin-4 in focal segmental glomerulosclerosis.J Am Soc Nephrol. 2005; 16: 3694-3701Crossref PubMed Scopus (141) Google Scholar, 9.Kaplan J.M. Kim S.H. North K.N. et al.Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.Nat Genet. 2000; 24: 251-256Crossref PubMed Scopus (1040) Google Scholar, 10.Reiser J. Polu K.R. Moller C.C. et al.TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.Nat Genet. 2005; 37: 739-744Crossref PubMed Scopus (680) Google Scholar, 21.Santin S. Ars E. Rossetti S. et al.TRPC6 mutational analysis in a large cohort of patients with focal segmental glomerulosclerosis.Nephrol Dial Transplant. 2009; 24: 3089-3096Crossref PubMed Scopus (81) Google Scholar, 22.Heeringa S.F. Moller C.C. Du J. et al.A novel TRPC6 mutation that causes childhood FSGS.PLoS One. 2009; 4: e7771Crossref PubMed Scopus (128) Google Scholar, 23.Zhu B. Chen N. Wang Z.H. et al.Identification and functional analysis of a novel TRPC6 mutation associated with late onset familial focal segmental glomerulosclerosis in Chinese patients.Mutat Res. 2009; 664: 84-90Crossref PubMed Scopus (54) Google Scholar Recently, mutations in exons 2 to 4 of the INF2 gene have been linked to AD-FSGS nephropathy and CMT neuropathy associated with FSGS. Interestingly, many of these are recurrent mutations (15 novel and10 recurrent mutations) with variable renal and neurological phenotypes.12.Brown E.J. Schlondorff J.S. Becker D.J. et al.Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis.Nat Genet. 2010; 42: 72-76Crossref PubMed Scopus (340) Google Scholar, 13.Lee H.K. Han K.H. Jung Y.H. et al.Variable renal phenotype in a family with an INF2 mutation.Pediatr Nephrol. 2010; 26: 73-76Crossref PubMed Scopus (27) Google Scholar, 14.Boyer O. Benoit G. Gribouval O. et al.Mutations in INF2 are a major cause of autosomal dominant focal segmental glomerulosclerosis.J Am Soc Nephrol. 2011; 22: 239-245Crossref PubMed Scopus (129) Google Scholar, 15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar, 16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar In this study, we describe the genetic screening and phenotypic analysis of a cohort of five families with AD-FSGS. After negative mutational analysis for ACTN4 and TRPC6, we found that one family carries a novel missense mutation (L245P) in exon 6 of INF2. We report the first novel mutation outside the candidate region for diagnosis of INF2, highlighting the need to sequence the entire gene if no mutations are found in exons 2 to 4. Furthermore, FSGS patients carrying the L245P mutation have no clinical or electrodiagnostic evidence of associated neuropathy, suggesting exon 6 as a region for nonsyndromic FSGS. Mutations in autosomal recessive genes NPHS1, NPHS2, CD2AP, and PLCE1 have been associated with severe FSGS, whereas mutations in ACTN4, TRPC6, and INF2 have been associated with a later-onset form of the disease.24.Pei Y. INF2 is another piece of the jigsaw puzzle for FSGS.J Am Soc Nephrol. 2011; 22: 197-199Crossref PubMed Scopus (5) Google Scholar All of the variants were found in podocyte genes that code for structural elements located in the glomerular slit diaphragm25.Mundel P. Reiser J. Proteinuria: an enzymatic disease of the podocyte?.Kidney Int. 2010; 77: 571-580Abstract Full Text Full Text PDF PubMed Scopus (228) Google Scholar and in proteins involved in the maintenance of the podocyte actin cytoskeleton. With the additional association of INF2 mutations with AD-FSGS, the understanding of this disease has increased. Mutations in the INF2 gene are major causes of familial AD-FSGS, with a prevalence of approximately 15% of all screened families in the world (n=195, including the one described in this article). This prevalence is in clear contrast to the contribution of mutations in TRPC6 (5.5%)9.Kaplan J.M. Kim S.H. North K.N. et al.Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.Nat Genet. 2000; 24: 251-256Crossref PubMed Scopus (1040) Google Scholar, 10.Reiser J. Polu K.R. Moller C.C. et al.TRPC6 is a glomerular slit diaphragm-associated channel required for normal renal function.Nat Genet. 2005; 37: 739-744Crossref PubMed Scopus (680) Google Scholar, 11.Winn M.P. Conlon P.J. Lynn K.L. et al.A mutation in the TRPC6 cation channel causes familial focal segmental glomerulosclerosis.Science. 2005; 308: 1801-1804Crossref PubMed Scopus (888) Google Scholar, 21.Santin S. Ars E. Rossetti S. et al.TRPC6 mutational analysis in a large cohort of patients with focal segmental glomerulosclerosis.Nephrol Dial Transplant. 2009; 24: 3089-3096Crossref PubMed Scopus (81) Google Scholar, 22.Heeringa S.F. Moller C.C. Du J. et al.A novel TRPC6 mutation that causes childhood FSGS.PLoS One. 2009; 4: e7771Crossref PubMed Scopus (128) Google Scholar, 23.Zhu B. Chen N. Wang Z.H. et al.Identification and functional analysis of a novel TRPC6 mutation associated with late onset familial focal segmental glomerulosclerosis in Chinese patients.Mutat Res. 2009; 664: 84-90Crossref PubMed Scopus (54) Google Scholar and ACTN4 (1.5%).5.Weins A. Kenlan P. Herbert S. et al.Mutational and biological analysis of alpha-actinin-4 in focal segmental glomerulosclerosis.J Am Soc Nephrol. 2005; 16: 3694-3701Crossref PubMed Scopus (141) Google Scholar,9.Kaplan J.M. Kim S.H. North K.N. et al.Mutations in ACTN4, encoding alpha-actinin-4, cause familial focal segmental glomerulosclerosis.Nat Genet. 2000; 24: 251-256Crossref PubMed Scopus (1040) Google Scholar A total of 69.3% (n=27) of all INF2 mutations previously identified cause nonsyndromic FSGS (exon 4: 61.5%, n=24; exon 2: 7.7%, n=3), whereas the remaining 30.7% result in syndromic FSGS (exon 2: 17.9%, n=7; exon3: 12.8%, n=5). Another distinctive characteristic of the INF2 gene is its ability to inherit recurrent mutations (23.8%) when compared with the ACTN4 and TRPC6 genes (none), which is a unique characteristic among the AD-FSGS genes (Figure 3b).12.Brown E.J. Schlondorff J.S. Becker D.J. et al.Mutations in the formin gene INF2 cause focal segmental glomerulosclerosis.Nat Genet. 2010; 42: 72-76Crossref PubMed Scopus (340) Google Scholar, 13.Lee H.K. Han K.H. Jung Y.H. et al.Variable renal phenotype in a family with an INF2 mutation.Pediatr Nephrol. 2010; 26: 73-76Crossref PubMed Scopus (27) Google Scholar, 14.Boyer O. Benoit G. Gribouval O. et al.Mutations in INF2 are a major cause of autosomal dominant focal segmental glomerulosclerosis.J Am Soc Nephrol. 2011; 22: 239-245Crossref PubMed Scopus (129) Google Scholar, 15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar, 16.Boyer O. Nevo F. Plaisier E. et al.INF2 mutations in Charcot-Marie-Tooth disease with glomerulopathy.N Engl J Med. 2011; 365: 2377-2388Crossref PubMed Scopus (204) Google Scholar Both aspects have led researchers to suggest that exons 2–4 of INF2 are candidate regions for a rapid, noninvasive, and cost-effective mutational screening for diagnosing AD-FSGS linked to INF2 gene.14.Boyer O. Benoit G. Gribouval O. et al.Mutations in INF2 are a major cause of autosomal dominant focal segmental glomerulosclerosis.J Am Soc Nephrol. 2011; 22: 239-245Crossref PubMed Scopus (129) Google Scholar,15.Gbadegesin R.A. Lavin P.J. Hall G. et al.Inverted formin 2 mutations with variable expression in patients with sporadic and hereditary focal and segmental glomeruloscerosis.Kidney Int. 2011; 81: 94-99Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar The INF2 protein is a member of the formin family of actin-regulatory proteins and has the following domains: a domain structure resembling an N-terminal DID17.Chhabra E.S. Higgs H.N. INF2 Is a WASP homology 2 motif-containing formin that severs actin filaments and accelerates both polymerization and depolymerization.J Biol Chem. 2006; 281: 26754-26767Crossref PubMed Scopus (151) Google Scholar; formin homology 1 and 2 domains26.Higgs H.N. Peterson K.J. Phylogenetic analysis of the formin homology 2 domain.Mol Biol Cell. 2005; 16: 1-13Crossref PubMed Scopus (201) Google Scholar,27.Pollard T.D. Regulation of actin filament assembly by Arp2/3 complex and formins.Annu Rev Biophys Biomol Struct. 2007; 36: 451-477Crossref PubMed Scopus (727) Google Scholar; and a C-terminal WASP Homology 2 domain, which has the hallmarks of the diaphanous autoregulatory domain (DAD) present in other formins (Figure 3b).17.Chhabra E.S. Higgs H.N. INF2 Is a WASP homology 2 motif-containing formin that severs actin filaments and accelerates both polymerization and depolymerization.J Biol Chem. 2006; 281: 26754-26767Crossref PubMed Scopus (151) Google Scholar The DID binds to the DAD, which autoinhibits the depolymerization but not the polymerization activity of INF2; this action is in contrast to other formins, where the DID/DAD binding inhibits both activities. Recently, Chhabra et al.28.Chhabra E.S. Ramabhadran V. Gerber S.A. et al.INF2 is an endoplasmic reticulum-associated formin protein.J Cell Sci. 2009; 122: 1430-1440Crossref PubMed Scopus (106) Google Scholar discovered that INF2 is predominantly localized in the endoplasmic reticulum and that mutations disrupting the DID/DAD interaction cause the endoplasmic reticulum to collapse because of the accumulation of actin filaments. When the DID/DAD interaction does not occur, actin polymerization is deregulated, which blocks the interaction of the INF2 protein with the formins of the DIA (diaphanous) group and alters the transport processes (transcytosis) mediated by the MAL protein and
Referência(s)