Novel INF2 mutations in an Italian cohort of patients with focal segmental glomerulosclerosis, renal failure and Charcot-Marie-Tooth neuropathy

Co-occurrence of Charcot-Marie-Tooth disease type 1 and glomerulosclerosis in a patient with a de novo INF2 variant

BACKGROUND

Renal disease is associated with Charcot-Marie-Tooth disease (CMT), a common inherited neurological disorder. Three forms of CMT have been identified: CMT1 of the demyelinating type, CMT2 of the axonal defect type, and intermediate type (Int-CMT). INF2 is an important target for variants that cause the complex symptoms of focal segmental glomerulosclerosis (FSGS) and CMT.

CASE PRESENTATION

We report the case of a 13-year-old female Chinese patient (born in 2011) with a rare co-occurrence of CMT1 and glomerulosclerosis (GS) (CMT1-GS). The patient presented with slowly progressive gait disorder with unsteadiness during walking, pes cavus, and kyphoscoliosis since the age of 1 year. Electrophysiological studies and brain magnetic resonance imaging revealed demyelinating features consistent with CMT1. At 12 years of age, she was hospitalised for hypertension and dizziness; her serum albumin was 27.9 g/L, serum creatinine was 87 μmol/L, estimated glomerular filtration rate was 88.6 mL/min, and 24-h urine protein was 4.95 g. A renal biopsy showed glomerulosclerosis. Renal function deteriorated further during the follow-up period, and she received a kidney transplant at the age of 13. Whole-exome sequencing identified a de novo heterozygous c.326T > G (p.Met109Arg) variant in exon 2 of INF2. The variant was classified as "pathogenic" according to the American College of Medical Genetics and Genomics criteria.

CONCLUSIONS

We describe a rare clinical phenotype of CMT1-GS associated with a de novo variant of INF2. Our findings expand the phenotypic and genotypic spectrums of INF2-associated disorders.

Hidden genetics behind glomerular scars: an opportunity to understand the heterogeneity of focal segmental glomerulosclerosis?

Focal segmental glomerulosclerosis (FSGS) is a complex disease which describes different kinds of kidney defects, not exclusively linked with podocyte defects. Since nephrin mutation was first described in association with early-onset nephrotic syndrome (NS), many advancements have been made in understanding genetic patterns associated with FSGS. New genetic causes of FSGS have been discovered, displaying unexpected genotypes, and recognizing possible site of damage. Many recent large-scale sequencing analyses on patients affected by idiopathic chronic kidney disease (CKD), kidney failure (KF) of unknown origin, or classified as FSGS, have revealed collagen alpha IV genes, as one of the most frequent sites of pathogenic mutations. Also, recent interest in complex and systemic lysosomal storage diseases, such as Fabry disease, has highlighted GLA mutations as possible causes of FSGS. Tubulointerstitial disease, recently classified by KDIGO based on genetic subtypes, when associated with UMOD variants, may phenotypically gain FSGS features, as well as ciliopathy genes or others, otherwise leading to completely different phenotypes, but found carrying pathogenic variants with associated FSGS phenotype. Thus, glomerulosclerosis may conceal different heterogeneous conditions. When a kidney biopsy is performed, the principal objective is to provide an accurate diagnosis. The broad spectrum of phenotypic expression and genetic complexity is demonstrating that a combined path of management needs to be applied. Genetic investigation should not be reserved only to selected cases, but rather part of medical management, integrating with clinical and renal pathology records. FSGS heterogeneity should be interpreted as an interesting opportunity to discover new pathways of CKD, requiring prompt genotype-phenotype correlation. In this review, we aim to highlight how FSGS represents a peculiar kidney condition, demanding multidisciplinary management, and in which genetic analysis may solve some otherwise unrevealed idiopathic cases. Unfortunately there is not a uniform correlation between specific mutations and FSGS morphological classes, as the same variants may be identified in familial cases or sporadic FSGS/NS or manifest a variable spectrum of the same disease. These non-specific features make diagnosis challenging. The complexity of FSGS genotypes requires new directions. Old morphological classification does not provide much information about the responsible cause of disease and misdiagnoses may expose patients to immunosuppressive therapy side effects, mistaken genetic counseling, and misguided kidney transplant programs.

INF2 and ROBO2 gene mutation in an Indian family with end stage renal failure and follow-up of renal transplantation

BACKGROUND

Accurate genetic diagnosis of end-stage renal disease patients with a family history of renal dysfunction is very essential. It not only helps in proper prognosis, but becomes crucial in designating donor for live related renal transplant. We here present a case of family with deleterious mutations in INF2 and ROBO2 and its importance of genetic testing before preparing for kidney transplantation.

CASE PRESENTATION

We report the case of a 29-year-female with end-stage renal disease and rapidly progressive renal failure. Mutational analysis revealed an Autosomal Dominant inheritance pattern and mutation in exon 4 of the INF2 gene (p. Thr215Ser) and exon 26 of the ROBO2 gene (p. Arg1371Cys). Her mother was diagnosed for CKD stage 4 with creatinine level of 4.3 mg/dL. Genetic variants (INF2 and ROBO2) identified in proband were tested in her sisters and mother. Her elder sister was positive for both heterozygous variants (INF2 and ROBO2). Her mother was positive for mutation in INF2 gene, and her donor elder sister did not showed mutation in INF2 gene and had mutation in ROBO2 gene without any clinical symptoms.

CONCLUSION

This case report emphasize that familial genetic screening has allowed us in allocating the donor selection in family where family member had history of genetic defect of Chronic Kidney Disease. Information of the causative renal disorder is extremely valuable for risk-assessment and planning of kidney transplantation.

INF2 mutations in patients with a broad phenotypic spectrum of Charcot-Marie-Tooth disease and focal segmental glomerulosclerosis

Mutations in INF2 are associated with the complex symptoms of Charcot-Marie-Tooth disease (CMT) and focal segmental glomerulosclerosis (FSGS). To date, more than 100 and 30 genes have been reported to cause these disorders, respectively. This study aimed to identify INF2 mutations in Korean patients with CMT. This study was conducted with 743 Korean families with CMT who were negative for PMP22 duplication. In addition, a family with FSGS was included in this study. INF2 mutations were screened using whole exome sequencing (WES) and filtering processes. As the results, four pathogenic INF2 mutations were identified in families with different clinical phenotypes: p.L78P and p.L132P in families with symptoms of both CMT and FSGS; p.C104Y in a family with CMT; and p.R218Q in a family with FSGS. Moreover, different CMT types were observed in families with CMT symptoms: CMT1 in two families and Int-CMT in another family. Hearing loss was observed in two families with CMT1. Pathogenicity was predicted by in silico analyses, and considerable conformational changes were predicted in the mutant proteins. Two mutations (p.L78P and p.C104Y) were unreported, and three families showed de novo mutations that were putatively occurred from fathers. This study suggests that patients with INF2 mutations show a broad phenotypic spectrum: CMT1, CMT1 + FSGS, CMTDIE + FSGS, and FSGS. Therefore, the genotype-phenotype correlation may be more complex than previously recognized. We believe that this study expands the clinical spectrum of patients with INF2 mutations and will be helpful in the molecular diagnosis of CMT and FSGS.

Formins in Human Disease

Almost 25 years have passed since a mutation of a formin gene, DIAPH1, was identified as being responsible for a human inherited disorder: a form of sensorineural hearing loss. Since then, our knowledge of the links between formins and disease has deepened considerably. Mutations of DIAPH1 and six other formin genes (DAAM2, DIAPH2, DIAPH3, FMN2, INF2 and FHOD3) have been identified as the genetic cause of a variety of inherited human disorders, including intellectual disability, renal disease, peripheral neuropathy, thrombocytopenia, primary ovarian insufficiency, hearing loss and cardiomyopathy. In addition, alterations in formin genes have been associated with a variety of pathological conditions, including developmental defects affecting the heart, nervous system and kidney, aging-related diseases, and cancer. This review summarizes the most recent discoveries about the involvement of formin alterations in monogenic disorders and other human pathological conditions, especially cancer, with which they have been associated. In vitro results and experiments in modified animal models are discussed. Finally, we outline the directions for future research in this field.

INF2 p.Arg214Cys mutation in a Chinese family with rapidly progressive renal failure and follow-up of renal transplantation: case report and literature review

Background

Heterozygous mutations in the inverted formin 2 (INF2) gene are related to secondary focal segmental glomerulosclerosis (FSGS), a rare secondary disease associated with rapidly progressive renal failure.

Case presentation

We report a patient with familial autosomal INF2 mutation manifesting nephritic syndromes and elevated serum creatinine levels. Mutational analysis revealed an autosomal dominant (AD) inheritance pattern and a mutation in exon 4 (p.Arg214Cys) of INF2 as the likely cause, which has not been previously described in an Asian family. The patient progressed to end-stage renal disease (ESRD) and received hemodialysis. His mother had undergone renal transplant 3 years earlier, and his grandmother had carried the p.Arg214Cys mutation for more than 80 years without any sign of renal dysfunction.

Conclusions

This is the first report to identify an association between a familial autosomal dominant INF2 p.Arg214Cys mutation and rapidly progressive renal disease in an Asian family. INF2 mutation analysis should not be restricted to individuals without family history of FSGS, rather it should also be performed on individuals for whom drug-based therapies are not effective. In this case, kidney transplant is an effective alternative.

Impaired Mitochondrial Mobility in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth (CMT) disease is a progressive, peripheral neuropathy and the most commonly inherited neurological disorder. Clinical manifestations of CMT mutations are typically limited to peripheral neurons, the longest cells in the body. Currently, mutations in at least 80 different genes are associated with CMT and new mutations are regularly being discovered. A large portion of the proteins mutated in axonal CMT have documented roles in mitochondrial mobility, suggesting that organelle trafficking defects may be a common underlying disease mechanism. This review will focus on the potential role of altered mitochondrial mobility in the pathogenesis of axonal CMT, highlighting the conceptional challenges and potential experimental and therapeutic opportunities presented by this "impaired mobility" model of the disease.

A Deregulated Stress Response Underlies Distinct INF2-Associated Disease Profiles

BACKGROUND

Monogenic diseases provide favorable opportunities to elucidate the molecular mechanisms of disease progression and improve medical diagnostics. However, the complex interplay between genetic and environmental factors in disease etiologies makes it difficult to discern the mechanistic links between different alleles of a single locus and their associated pathophysiologies. Inverted formin 2 (INF2), an actin regulator, mediates a stress response-calcium mediated actin reset, or CaAR-that reorganizes the actin cytoskeleton of mammalian cells in response to calcium influx. It has been linked to the podocytic kidney disease focal segemental glomerulosclerosis (FSGS), as well as to cases of the neurologic disorder Charcot-Marie-Tooth disease that are accompanied by nephropathy, mostly FSGS.

METHODS

We used a combination of quantitative live cell imaging and validation in primary patient cells and Drosophila nephrocytes to systematically characterize a large panel of >50 autosomal dominant INF2 mutants that have been reported to cause either FSGS alone or with Charcot-Marie-Tooth disease.

RESULTS

We found that INF2 mutations lead to deregulated activation of formin and a constitutive stress response in cultured cells, primary patient cells, and Drosophila nephrocytes. We were able to clearly distinguish between INF2 mutations that were linked exclusively to FSGS from those that caused a combination of FSGS and Charcot-Marie-Tooth disease. Furthermore, we were able to identify distinct subsets of INF2 variants that exhibit varying degrees of activation.

CONCLUSIONS

Our results suggest that CaAR can be used as a sensitive assay for INF2 function and for robust evaluation of diseased-linked variants of formin. More broadly, these findings indicate that cellular profiling of disease-associated mutations has potential to contribute substantially to sequence-based phenotype predictions.

The formin INF2 in disease: progress from 10 years of research

Formins are a conserved family of proteins that primarily act to form linear polymers of actin. Despite their importance to the normal functioning of the cytoskeleton, for a long time, the only two formin genes known to be a genetic cause of human disorders were DIAPH1 and DIAPH3, whose mutation causes two distinct forms of hereditary deafness. In the last 10 years, however, the formin INF2 has emerged as an important target of mutations responsible for the appearance of focal segmental glomerulosclerosis, which are histological lesions associated with glomerulus degeneration that often leads to end-stage renal disease. In some rare cases, focal segmental glomerulosclerosis concurs with Charcot-Marie-Tooth disease, which is a degenerative neurological disorder affecting peripheral nerves. All known INF2 gene mutations causing disease map to the exons encoding the amino-terminal domain. In this review, we summarize the structure, biochemical features and functions of INF2, conduct a systematic and comprehensive analysis of the pathogenic INF2 mutations, including a detailed study exon-by-exon of patient cases and mutations, address the impact of the pathogenic mutations on the structure, regulation and known functions of INF2, draw a series of conclusions that could be useful for INF2-related disease diagnosis, and suggest lines of research for future work on the molecular mechanisms by which INF2 causes disease.

The Maintenance of Mitochondrial DNA Integrity and Dynamics by Mitochondrial Membranes

Mitochondria are complex organelles that harbour their own genome. Mitochondrial DNA (mtDNA) exists in the form of a circular double-stranded DNA molecule that must be replicated, segregated and distributed around the mitochondrial network. Human cells typically possess between a few hundred and several thousand copies of the mitochondrial genome, located within the mitochondrial matrix in close association with the cristae ultrastructure. The organisation of mtDNA around the mitochondrial network requires mitochondria to be dynamic and undergo both fission and fusion events in coordination with the modulation of cristae architecture. The dysregulation of these processes has profound effects upon mtDNA replication, manifesting as a loss of mtDNA integrity and copy number, and upon the subsequent distribution of mtDNA around the mitochondrial network. Mutations within genes involved in mitochondrial dynamics or cristae modulation cause a wide range of neurological disorders frequently associated with defects in mtDNA maintenance. This review aims to provide an understanding of the biological mechanisms that link mitochondrial dynamics and mtDNA integrity, as well as examine the interplay that occurs between mtDNA, mitochondrial dynamics and cristae structure.

Mutation of microphthalmia-associated transcription factor (mitf) in zebrafish sensitizes for glomerulopathy

Different glomerular diseases that affect podocyte homeostasis can clinically present as nephrotic syndrome with massive proteinuria, hypoalbuminemia, hyperlipidemia and edema. Up to now, no drugs that specifically target the actin cytoskeleton of podocytes are on the market and model systems for library screenings to develop anti-proteinuric drugs are of high interest. We developed a standardized proteinuria model in zebrafish using puromycin aminonucleoside (PAN) via treatment in the fish water to allow for further drug testing to develop anti-proteinuric drugs for the treatment of glomerular diseases. We noticed that fish that carry the nacre-mutation show a significantly higher susceptibility for the disruption of the glomerular filtration barrier following PAN treatment, which results in a more pronounced proteinuria phenotype. Nacre zebrafish inherit a mutation yielding a truncated version of microphthalmia-associated transcription factor/melanogenesis associated transcription factor (mitf). We hypothesized that the nacre mutation may lead to reduced formin expression and defects in cytoskeletal rearrangement. Based on the observations in zebrafish, we carried out a PAN treatment on cultured human podocytes after knockdown with MITF siRNA causing a rearrangement of the actin cytoskeleton.

Proteinuric Kidney Diseases: A Podocyte's Slit Diaphragm and Cytoskeleton Approach

Proteinuric kidney diseases are a group of disorders with diverse pathological mechanisms associated with significant losses of protein in the urine. The glomerular filtration barrier (GFB), comprised of the three important layers, the fenestrated glomerular endothelium, the glomerular basement membrane (GBM), and the podocyte, dictates that disruption of any one of these structures should lead to proteinuric disease. Podocytes, in particular, have long been considered as the final gatekeeper of the GFB. This specialized visceral epithelial cell contains a complex framework of cytoskeletons forming foot processes and mediate important cell signaling to maintain podocyte health. In this review, we will focus on slit diaphragm proteins such as nephrin, podocin, TRPC6/5, as well as cytoskeletal proteins Rho/small GTPases and synaptopodin and their respective roles in participating in the pathogenesis of proteinuric kidney diseases. Furthermore, we will summarize the potential therapeutic options targeting the podocyte to treat this group of kidney diseases.

Mutational screening of inverted formin 2 in adult-onset focal segmental glomerulosclerosis or minimal change patients from the Czech Republic

Background

Mutations in INF2 are frequently responsible for focal segmental glomerulosclerosis (FSGS), which is a common cause of end stage renal disease (ESRD); additionally, they are also connected with Charcot-Marie-Tooth neuropathy. INF2 encodes for inverted formin 2. This protein participates in regulation of the dynamics of the actin cytoskeleton, involving not only the polymerisation, but also the depolymerisation of filaments. The present study is the first mutational analysis of INF2 done in the Czech Republic.

Methods

Mutational analysis of INF2 was performed on 109 patients (mean age at onset 41.44 ± 18.91 years) with FSGS or minimal change disease (MCD); and also in 6 patients without renal biopsy who had already developed chronic kidney disease (CKD)/ESRD at the time of diagnosis. We used high resolution melting method (HRM), with subsequent Sanger sequencing, in suspect samples from HRM analysis. The HRM method is an effective method for the screening of large cohorts of patients.

Results

Two pathogenic mutations (p.Arg214His and p.Arg218Gln) were detected in INF2. The first (p.Arg214His) was identified in the FSGS patient with a positive family history. The second mutation (p.Arg218Gln) was found in two brothers with ESRD of unknown etiology. The most frequent sequence change was the substitution p.P35P, the incidence of which corresponded with the frequencies available in the ExAC Browser and gnomAD Browser databases. This analysis also detected different exonic and intronic changes that probably did not influence the phenotype of the included patients.

Conclusions

The INF2 mutational screening is useful in familial FSGS cases as well as in patients with an unknown cause for their ESRD, but with a positive family history. INF2 seems to be not only the cause of FSGS, but also of ESRD of unknown etiology. Our study has confirmed that the HRM analysis is a very useful method for the identification of single nucleotide substitutions.

Clinical genetic testing using a custom-designed steroid-resistant nephrotic syndrome gene panel: analysis and recommendations

BACKGROUND

There are many single-gene causes of steroid-resistant nephrotic syndrome (SRNS) and the list continues to grow rapidly. Prompt comprehensive diagnostic testing is key to realising the clinical benefits of a genetic diagnosis. This report describes a bespoke-designed, targeted next-generation sequencing (NGS) diagnostic gene panel assay to detect variants in 37 genes including the ability to identify copy number variants (CNVs).

METHODS

This study reports results of 302 patients referred for SRNS diagnostic gene panel analysis. Phenotype and clinical impact data were collected using a standard proforma. Candidate variants detected by NGS were confirmed by Sanger sequencing/Multiplex Ligation-dependent Probe Amplification with subsequent family segregation analysis where possible.

RESULTS

Clinical presentation was nephrotic syndrome in 267 patients and suspected Alport syndrome (AS) in 35. NGS panel testing determined a likely genetic cause of disease in 44/220 (20.0%) paediatric and 10/47 (21.3%) adult nephrotic cases, and 17/35 (48.6%) of haematuria/AS patients. Of 71 patients with genetic disease, 32 had novel pathogenic variants without a previous disease association including two with deletions of one or more exons of NPHS1 or NPHS2.

CONCLUSION

Gene panel testing provides a genetic diagnosis in a significant number of patients presenting with SRNS or suspected AS. It should be undertaken at an early stage of the care pathway and include the ability to detect CNVs as an emerging mechanism for genes associated with this condition. Use of clinical genetic testing after diagnosis of SRNS has the potential to stratify patients and assist decision-making regarding management.

Inverted formins: A subfamily of atypical formins

Formins are a family of regulators of actin and microtubule dynamics that are present in almost all eukaryotes. These proteins are involved in many cellular processes, including cytokinesis, stress fiber formation, and cell polarization. Here we review one subfamily of formins, the inverted formins. Inverted formins as a group break several formin stereotypes, having atypical biochemical properties and domain organization, and they have been linked to kidney disease and neuropathy in humans. In this review, we will explore recent research on members of the inverted formin sub-family in mammals, zebrafish, fruit flies, and worms.

Thrombotic Microangiopathy in Inverted Formin 2-Mediated Renal Disease

The demonstration of impaired C regulation in the thrombotic microangiopathy (TMA) atypical hemolytic uremic syndrome (aHUS) resulted in the successful introduction of the C inhibitor eculizumab into clinical practice. C abnormalities account for approximately 50% of aHUS cases; however, mutations in the non-C gene diacylglycerol kinase-ε have been described recently in individuals not responsive to eculizumab. We report here a family in which the proposita presented with aHUS but did not respond to eculizumab. Her mother had previously presented with a post-renal transplant TMA. Both the proposita and her mother also had Charcot-Marie-Tooth disease. Using whole-exome sequencing, we identified a mutation in the inverted formin 2 gene (INF2) in the mutational hotspot for FSGS. Subsequent analysis of the Newcastle aHUS cohort identified another family with a functionally-significant mutation in INF2 In this family, renal transplantation was associated with post-transplant TMA. All individuals with INF2 mutations presenting with a TMA also had aHUS risk haplotypes, potentially accounting for the genetic pleiotropy. Identifying individuals with TMAs who may not respond to eculizumab will avoid prolonged exposure of such individuals to the infectious complications of terminal pathway C blockade.

Reduced INF2 expression in nephrotic syndrome is possibly related to clinical severity of steroid resistance in children

AIM

Mutations of the inverted formin 2 gene (INF2), which encodes a member of the formin family, cause autosomal dominant focal segmental glomerulosclerosis (FSGS) and Charcot-Marie-Tooth (CMT) disease-associated FSGS. However, their role in idiopathic FSGS remains unclear. This study investigated INF2 localization in the normal adult kidney and its expression in children with idiopathic nephrotic syndrome.

METHODS

We generated a rabbit polyclonal antibody against the conjugated peptide from human INF2 and studied the glomerular expression of INF2 and synaptopodin using normal human adult kidney tissues and tissues from children with glomerular diseases such as minimal change disease (MCD), FSGS, IgA nephropathy (IgAN), non-IgA mesangial proliferative glomerulonephritis (non-IgAN), and Henoch-Schönlein purpura nephritis (HSPN).

RESULTS

The anti-INF2 antibody detected an approximately 140-kD fragment isolated from adult mature glomeruli by western blotting. Immunohistochemically, INF2 was detected in podocytes and renal arteries. Among 56 patients, INF2 in glomeruli was expressed at a similar level in patients with MCD, IgAN, non-IgAN, or HSPN and controls. In FSGS patients, INF2 expression in glomeruli was either decreased or absent. There was a relationship between decreased INF2 expression and the clinical severity of steroid resistant nephrotic syndrome (SRNS).

CONCLUSION

We propose that examination of INF2 expression may help to differentiate MCD from FSGS and evaluate the clinical severity of SRNS in children.

Diagnosing FSGS without kidney biopsy - a novel INF2-mutation in a family with ESRD of unknown origin

Background

Patients on renal replacement therapy are often unaware of their underlying condition and hence suffer from so-called end-stage renal disease (ESRD) of unknown origin. However, an exact diagnosis is not only important for better estimating the prognosis, but also when preparing for kidney transplantation. Whilst patients with FSGS without a confirmed genetic cause have a high recurrence rate in the transplanted organ, patients with a mutation generally exhibit no recurrence and have a good prognosis. Furthermore, renal biopsy, which may be helpful for differential diagnosis, is usually contraindicated in end-stage kidneys. We here present the case of familial ESRD of unknown origin, which could be resolved by targeted genetic testing prior to planning of kidney transplantation.

Case presentation

A 32-year-old female with ESRD and nephrotic range proteinuria was admitted to our clinic. Family-history revealed that both mother and maternal grandmother had ESRD of unknown origin. As renal biopsy was impossible due to atrophic kidneys, we performed mutation analysis of genes known for dominant forms of FSGS and found a novel heterozygous mutation of INF2 (c.485 T > C, p.Leu162Pro). The same mutation could be detected in the index patient’s mother (ESRD at age 50) and three brothers with normal serum-creatinine but mid or low range proteinuria.

Conclusions

Genetic testing is warranted in families with ESRD of unknown origin and may provide a robust diagnosis even without kidney biopsy. It will help detecting relatives at risk who have to be excluded from potential kidney donation and who may benefit from timely initiation of protective measures in order to slow down disease progression.

Charcot-Marie-Tooth diseases: an update and some new proposals for the classification

BACKGROUND

Charcot-Marie-Tooth (CMT) disease, the most frequent form of inherited neuropathy, is a genetically heterogeneous group of disorders of the peripheral nervous system, but with a quite homogeneous clinical phenotype (progressive distal muscle weakness and atrophy, foot deformities, distal sensory loss and usually decreased tendon reflexes). Our aim was to review the various CMT subtypes identified at the present time.

METHODS

We have analysed the medical literature and performed a historical retrospective of the main steps from the individualisation of the disease (at the end of the nineteenth century) to the recent knowledge about CMT.

RESULTS

To date, >60 genes (expressed in Schwann cells and neurons) have been implicated in CMT and related syndromes. The recent advances in molecular genetic techniques (such as next-generation sequencing) are promising in CMT, but it is still useful to recognise some specific clinical or pathological signs that enable us to validate genetic results. In this review, we discuss the diagnostic approaches and the underlying molecular pathogenesis.

CONCLUSIONS

We suggest a modification of the current classification and explain why such a change is needed.

Novel mutations in the inverted formin 2 gene of Chinese families contribute to focal segmental glomerulosclerosis

Here, we report a genetic study of an extended family of Chinese ancestry with focal segmental glomerulosclerosis (FSGS), with one of the affected members also concurrently diagnosed with IgA nephropathy (IgAN). By genome-wide linkage analysis and subsequent sequencing, we identified an S85W mutation in the inverted formin 2 (INF2) gene that perfectly cosegregated with the kidney disease phenotype. The entire INF2 coding region was sequenced in 200 healthy controls, 55 families with FSGS, and 34 families with IgAN. This analysis identified a novel insertion, S129_Q130insVRQLS, in another FSGS pedigree. In vitro studies found that α-actinin 4 expression was decreased and INF2 showed perinuclear localization in S85W-transfected podocytes. Phosphorylation of serum response factor, and that its nuclear translation was decreased in S85W podocytes, indicated decreased activation in mutants. Abnormal actin organization was also found in S85W podocytes, while no change of microtubule structure was observed. Co-immunoprecipitation and immunofluorescence found decreased interaction between INF2 and Cdc42 in S85W podocytes. However, all these changes were not found in S129_Q130insVRQLS podocytes. The overall frequency of INF2 mutations was ~3.6% among Chinese familial FSGS, which was considerably lower than that from studies of European FSGS families. Thus, S85W but not the S129_Q130insVRQLS variant leads to podocyte cytoskeletal abnormalities, probably by impaired serum response factor phosphorylation.

LPS nephropathy in mice is ameliorated by IL-2 independently of regulatory T cells activity

Immunosuppressive regulatory T cells (Tregs) have been hypothesized to exert a protective role in animal models of spontaneous (Buffalo/Mna) and/or drug induced (Adriamycin) nephrotic syndrome. In this study, we thought to define whether Tregs can modify the outcome of LPS nephropathy utilizing IL-2 as inducer of tissue and circulating Tregs. LPS (12 mg/Kg) was given as single shot in C57BL/6, p2rx7⁻/⁻ and Foxp3EGFP; free IL-2 (18.000 U) or, in alternative, IL-2 coupled with JES6-1 mAb (IL-2/anti-IL-2) were injected before LPS. Peripheral and tissue Tregs/total CD4+ cell ratio, urinary parameters and renal histology were evaluated for 15 days. IL-2 administration to wild type mice had no effect on peripheral Tregs number, whereas a significant increase was induced by the IL-2/anti-IL-2 immunocomplex after 5 days. Spleen and lymph nodes Tregs were comparably increased. In p2rx7⁻/⁻ mice, IL-2/anti-IL-2 treatment resulted in increase of peripheral Tregs but did not modify the spleen and lymph nodes quota. LPS induced comparable and transient proteinuria in both wild type and p2rx7⁻/⁻ mice. Proteinuria was inhibited by co-infusion of human IL-2, with reduction at each phase of the disease (24 -48 and 72 hours) whereas IL-2/anti-IL-2 produced weaker effects. In all mice (wild type and p2rx7⁻/⁻) and irrespective of treatment (IL-2, IL-2/anti-IL-2), LPS was associated with progressive signs of renal pathologic involvement resulting in glomerulosclerosis. In conclusion, IL-2 plays a transient protective effect on proteinuria induced by LPS independent of circulating or tissue Tregs but does not modify the outcome of renal degenerative renal lesions.

Intermediate Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (CMT) disease is a common neurogenetic disorder and its heterogeneity is a challenge for genetic diagnostics. The genetic diagnostic procedures for a CMT patient can be explored according to the electrophysiological criteria: very slow motor nerve conduction velocity (MNCV) (<15 m/s), slow MNCV (15-25 m/s), intermediate MNCV (25-45 m/s), and normal MNCV (>45 m/s). Based on the inheritance pattern, intermediate CMT can be divided into dominant (DI-CMT) and recessive types (RI-CMT). GJB1 is currently considered to be associated with X-linked DI-CMT, and MPZ, INF2, DNM2, YARS, GNB4, NEFL, and MFN2 are associated with autosomal DI-CMT. Moreover, GDAP1, KARS, and PLEKHG5 are associated with RI-CMT. Identification of these genes is not only important for patients and families but also provides new information about pathogenesis. It is hoped that this review will lead to a better understanding of intermediate CMT and provide a detailed diagnostic procedure for intermediate CMT.