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Mutations in the Immunoglobulin mu DNA binding protein 2 (IGHMBP2) gene result in two distinct diseases, SMA with Respiratory Distress Type I (SMARD1) and Charcot Marie Tooth Type 2S (CMT2S). To understand the phenotypic and molecular differences between SMARD1 and CMT2S, and the role of IGHMBP2 in disease development, we generated mouse models based on six IGHMBP2 patient mutations. Previously, we reported the development and characterization of Ighmbp2D564N/D564N mice and in this manuscript, we examine two mutations: D565N (D564N in mice) and H924Y (H922Y in mice) in the Ighmbp2H922Y/H922Y and Ighmbp2D564N/H922Y contexts. We found significant differences between these mouse models, providing critical insight into the role of IGHMBP2 in the pathogenesis of SMARD1 and CMT2S. Importantly, these studies also demonstrate how disease pathogenesis is significantly altered in the context of Ighmbp2 D564N and H922Y homozygous recessive and compound heterozygous mutations. Notably, there were short-lived and long-lived lifespan cohorts within Ighmbp2D564N/H922Y mice with early (P12/P16) respiratory pathology serving as a key predictor of lifespan. Despite differences in lifespan, motor function deficits initiated early and progressively worsened in all Ighmbp2D564N/H922Y mice. There was decreased limb skeletal muscle fiber area and increased neuromuscular junction (NMJ) denervation in Ighmbp2D564N/H922Y mice. Consistent with CMT2S, Ighmbp2H922Y/H922Y mice did not have altered lifespans nor respiratory pathology. Interestingly, Ighmbp2H922Y/H922Y limb muscle fibers demonstrated an increase in muscle fiber area followed by a reduction while changes in NMJ innervation were minimal even at P180. This is the first study that demonstrates differences associated with IGHMBP2 function within respiration with those within limb motor function. Significant to our understanding of IGHMBP2 function, we demonstrate that there is a direct correlation between disease pathogenesis associated with these IGHMBP2 patient mutations and IGHMBP2 biochemical activity. Importantly, these studies reveal the dynamic differences that are presented when either a single mutant protein is present (IGHMBP2-D564N or IGHMBP2-H922Y) or two mutant proteins are present (IGHMBP2-D564N and IGHMBP2-H922Y) within cells.
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Distal hereditary motor neuropathies (dHMN) are a group of heterogeneous diseases and previous studies have reported that the compound heterozygous recessive MME variants cause dHMN. Our study found a novel homozygous MME variant and a reported compound heterozygous MME variant in two Chinese families, respectively. Next-generation sequencing and nerve conduction studies were performed for two probands. The probands in two families presented with the muscle weakness and wasting of both lower limbs and carried a c.2122 A > T (p.K708*) and c.1342 C > T&c.2071_2072delinsTT (p.R448*&p.A691L) variant, respectively. Prominently axonal impairment of motor nerves and slight involvement of sensory nerves were observed in nerve conduction study. Our study reported a "novel" nonsense mutation and a missense variant of autosomal recessive late-onset dHMN and reviewed reported MME variants associated with dHMN phenotype.
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Neuropatia Hereditária Motora e Sensorial , Neprilisina , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Idade de Início , Alelos , China , Códon sem Sentido , População do Leste Asiático/genética , Genes Recessivos , Neuropatia Hereditária Motora e Sensorial/genética , Linhagem , Neprilisina/genéticaRESUMO
BACKGROUND AND AIMS: Charcot-Marie-Tooth (CMT) is a heterogeneous group of genetic neuropathies and is typically characterized by distal muscle weakness, sensory loss, pes cavus and areflexia. Herein we describe a case of CMT2CC presenting with proximal muscle weakness and equivocal electrophysiological features, that was misdiagnosed as chronic inflammatory demyelinating polyneuropathy (CIDP). CASE REPORT: A 30-year-old woman complained of proximal muscle weakness with difficulty climbing stairs. Neurological examination showed weakness in lower limb (LL) muscles, that was marked proximally and mild distally, and absence of deep tendon reflexes in the ankles. Nerve conduction studies (NCS) showed sensory-motor neuropathy with non-uniform NC velocity and a partial conduction block (CBs) in peroneal nerve and tibial nerves. Thus, a diagnosis of CIDP was entertained and the patient underwent ineffective treatment with intravenous immunoglobulins. At electrophysiological revaluation CB in peroneal nerve was undetectable as also distal CMAP had decreased whereas the CBs persisted in tibial nerves. Hypothesizing a hereditary neuropathy, we examined the proband's son, who presented mild weakness of distal and proximal muscles at lower limbs. Neurophysiological investigation showed findings consistent with an intermediate-axonal electrophysiological pattern. A targeted-NGS including 136 CMT genes showed the heterozygous frameshift mutation (c.3057dupG; p.K1020fs*43) in the NEFH gene, coding for the neurofilament heavy chain and causing CMT2CC. INTERPRETATION: Diagnosis of a genetic neuropathy may be challenging when clinical features are atypical and/or electrophysiological features are misleading. The most common misdiagnosis is CIDP. Our report suggests that also CMT2CC patients with proximal muscle weakness and equivocal electrophysiological features might be misdiagnosed as CIDP.
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Charcot-Marie-Tooth type 2A (CMT2A) is a single-gene motor sensory neuropathy caused by Mfn2 mutation. It is generally believed that CMT2A involves mitochondrial fusion disruption. However, how Mfn2 mutation mediates the mitochondrial membrane fusion loss and its further pathogenic mechanisms remain unclear. Here, in vivo and in vitro mouse models harboring the Mfn2R364W, Mfn2G176S and Mfn2H165R mutations were constructed. Mitochondrial membrane fusion and fission proteins analysis showed that Mfn2R364W, Mfn2G176S, and Mfn2H165R/+ mutations maintain the expression of Mfn2, but promote Drp1 upregulation and Opa1 hydrolytic cleavage. In Mfn2H165R/H165R mutation, Mfn2, Drp1, and Opa1 all play a role in inducing mitochondrial fragmentation, and the mitochondrial aggregation is affected by Mfn2 loss. Further research into the pathogenesis of CMT2A showed these three mutations all induce mitochondria-mediated apoptosis, and mitochondrial oxidative phosphorylation damage. Overall, loss of overall fusion activity affects mitochondrial DNA (mtDNA) stability and causes mitochondrial loss and dysfunction, ultimately leading to CMT2A disease. Interestingly, the differences in the pathogenesis of CMT2A between Mfn2R364W, Mfn2G176S, Mfn2H165R/+ and Mfn2H165R/H165R mutations, including the distribution of Mfn2 and mitochondria, the expression of mitochondrial outer membrane-associated proteins (Bax, VDAC1 and AIF), and the enzyme activity of mitochondrial complex I, are related to the expression of Mfn2.
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Apoptose , Doença de Charcot-Marie-Tooth , GTP Fosfo-Hidrolases , Mitocôndrias , Mutação , Fosforilação Oxidativa , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/metabolismo , Doença de Charcot-Marie-Tooth/patologia , GTP Fosfo-Hidrolases/genética , GTP Fosfo-Hidrolases/metabolismo , Animais , Mitocôndrias/metabolismo , Mitocôndrias/genética , Camundongos , Apoptose/genética , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Dinâmica Mitocondrial/genética , Humanos , Modelos Animais de DoençasRESUMO
Immunoglobulin Mu-binding protein 2 (IGHMBP2) pathogenic variants result in the fatal, neurodegenerative disease spinal muscular atrophy with respiratory distress type 1 (SMARD1) and the milder, Charcot-Marie-Tooth (CMT) type 2S (CMT2S) neuropathy. More than 20 years after the link between IGHMBP2 and SMARD1 was revealed, and 10 years after the discovery of the association between IGHMBP2 and CMT2S, the pathogenic mechanism of these diseases is still not well defined. The discovery that IGHMBP2 functions as an RNA/DNA helicase was an important step, but it did not reveal the pathogenic mechanism. Helicases are enzymes that use ATP hydrolysis to catalyse the separation of nucleic acid strands. They are involved in numerous cellular processes, including DNA repair and transcription; RNA splicing, transport, editing and degradation; ribosome biogenesis; translation; telomere maintenance; and homologous recombination. IGHMBP2 appears to be a multifunctional factor involved in several cellular processes that regulate gene expression. It is difficult to determine which processes, when dysregulated, lead to pathology. Here, we summarise our current knowledge of the clinical presentation of IGHMBP2-related diseases. We also overview the available models, including yeast, mice and cells, which are used to study the function of IGHMBP2 and the pathogenesis of the related diseases. Further, we discuss the structure of the IGHMBP2 protein and its postulated roles in cellular functioning. Finally, we present potential anomalies that may result in the neurodegeneration observed in IGHMBP2-related disease and highlight the most prominent ones.
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Proteínas de Ligação a DNA , Atrofia Muscular Espinal , Fatores de Transcrição , Humanos , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Animais , Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/patologia , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/patologia , Síndrome do Desconforto Respiratório do Recém-Nascido/genéticaRESUMO
Dominant missense mutations of the calcium-permeable cation channel TRPV4 cause Charcot-Marie-Tooth disease (CMT) type 2C and two forms of distal spinal muscular atrophy. These conditions are collectively referred to as TRPV4-related neuromuscular disease and share features of motor greater than sensory dysfunction and frequent vocal fold weakness. Pathogenic variants lead to gain of ion channel function that can be rescued by TRPV4 antagonists in cellular and animal models. As small molecule TRPV4 antagonists have proven safe in trials for other disease indications, channel inhibition is a promising therapeutic strategy for TRPV4 patients. However, the current knowledge of the clinical features and natural history of TRPV4-related neuromuscular disease is insufficient to enable rational clinical trial design. To address these issues, we developed a TRPV4 patient database and administered a TRPV4-specific patient questionnaire. Here, we report demographic and clinical information, including CMT examination scores (CMTES), from 68 patients with known pathogenic TRPV4 variants, 40 of whom also completed the TRPV4 patient questionnaire. TRPV4 patients showed a bimodal age of onset, with the largest peak occurring in the first 2 years of life. Compared to CMT1A patients, TRPV4 patients showed distinct symptoms and signs, manifesting more ambulatory difficulties and more frequent involvement of proximal arm and leg muscles. Although patients reported fewer sensory symptoms, sensory dysfunction was often detected clinically. Many patients were affected by vocal fold weakness (55%) and shortness of breath (55%), and 11% required ventilatory support. Skeletal abnormalities were common, including scoliosis (64%), arthrogryposis (33%), and foot deformities. Strikingly, patients with infantile onset of disease showed less sensory involvement and less progression of symptoms. These results highlight distinctive clinical features in TRPV4 patients, including motor-predominant disease, proximal arm and leg weakness, severe ambulatory difficulties, vocal fold weakness, respiratory dysfunction, and skeletal involvement. In addition, patients with infantile onset of disease appeared to have a distinct phenotype with less apparent disease progression based on CMTES. These collective observations indicate that clinical trial design for TRPV4-related neuromuscular disease should include outcome measures that reliably capture non-length dependent motor dysfunction, vocal fold weakness, and respiratory disease.
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Distal hereditary motor neuropathies (dHMN) are a group of heterogeneous hereditary disorders characterized by a slowly progressive distal pure motor neuropathy. Electrophysiology, with normal motor and sensory conduction velocities, can suggest the diagnosis of dHMN and guide the genetic study. More than thirty genes are currently associated with HMNs, but around 60 to 70% of cases of dHMN remain uncharacterized genetically. Recent cohort studies showed that HSPB1, GARS, BICB2 and DNAJB2 are among the most frequent dHMN genes and that the prevalence of the disease was calculated as 2.14 and 2.3 per 100,000. The determination of the different genes involved in dHMNs made it possible to observe a genotypic overlap with some other neurogenetic disorders and other hereditary neuropathies such as CMT2, mainly with the HSPB1, HSPB8, BICD2 and TRPV4 genes of AD-inherited transmission and recently observed with SORD gene of AR transmission which seems relatively frequent and potentially curable. Distal hereditary motor neuropathy that predominates in the upper limbs is linked mainly to three genes: GARS, BSCL2 and REEP1, whereas dHMN with vocal cord palsy is associated with SLC5A7, DCTN1 and TRPV4 genes. Among the rare AR forms of dHMN like IGHMBP2 and DNAJB2, the SIGMAR1 gene mutations as well as VRK1 variants are associated with a motor neuropathy phenotype often associated with upper motoneuron involvement. The differential diagnosis of these latter arises with juvenile forms of amyotrophic lateral sclerosis, that could be caused also by variations of these genes, as well as hereditary spastic paraplegia. A differential diagnosis of dHMN related to Brown Vialetto Van Laere syndrome due to riboflavin transporter deficiency is important to consider because of the therapeutic possibility.
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BACKGROUND AND AIMS: This study aimed to report nine Charcot-Marie-Tooth disease (CMT) families with six novel IGHMBP2 mutations in our CMT2 cohort and to summarize the genetic and clinical features of all AR-CMT2S patients reported worldwide. METHODS: General information, clinical and neurophysiological data of 275 axonal CMT families were collected. Genetic screening was performed by inherited peripheral neuropathy related genes panel or whole exome sequencing. The published papers reporting AR-CMT2S from 2014 to 2023 were searched in Pubmed and Wanfang databases. RESULTS: In our CMT2 cohort, we detected 17 AR-CMT2S families carrying IGHMBP2 mutations and eight were published previously. Among these, c.743 T > A (p.Val248Glu), c.884A > G (p.Asp295Gly), c.1256C > A (p.Ser419*), c.2598_2599delGA (p.Lys868Sfs*16), c.1694_1696delATG (p.Asp565del) and c.2509A > T (p.Arg837*) were firstly reported. These patients prominently presented with early-onset typical axonal neuropathy and without respiratory dysfunction. So far, 56 AR-CMT2S patients and 57 different mutations coming from 43 families have been reported in the world. Twenty-nine of 32 missense mutations were clustered in helicase domain and ATPase region. The age at onset ranged from 0.11to 20 years (Mean ± SD: 3.43 ± 3.88 years) and the majority was infantile-onset (<2 years). The initial symptoms included weakness of limbs (19, 29.7%), delayed milestones (12, 18.8%), gait disturbance (11, 17.2%), feet deformity (8, 12.5%), feet drop (8, 12.5%), etc. INTERPRETATION: AR-CMT2S accounted for 6.2% in our CMT2 cohort. We firstly reported six novel IGHMBP2 mutations which expanded the genotypic spectrum of AR-CMT2S. Furthermore, 17 AR-CMT2S families could provide more resources for natural history study, drug research and development.
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Doença de Charcot-Marie-Tooth , Estudos de Associação Genética , Humanos , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/fisiopatologia , Feminino , Masculino , Adulto , China/epidemiologia , Estudos de Coortes , Adolescente , Criança , Mutação , Fatores de Transcrição/genética , Adulto Jovem , Proteínas de Ligação a DNA/genética , Pessoa de Meia-Idade , Linhagem , Pré-EscolarRESUMO
Mutations in the gene encoding MFN2 have been identified as associated with Charcot-Marie-Tooth disease type 2A (CMT2A), a neurological disorder characterized by a broad clinical phenotype involving the entire nervous system. MFN2, a dynamin-like GTPase protein located on the outer mitochondrial membrane, is well-known for its involvement in mitochondrial fusion. Numerous studies have demonstrated its participation in a network crucial for various other mitochondrial functions, including mitophagy, axonal transport, and its controversial role in endoplasmic reticulum (ER)-mitochondria contacts. Considerable progress has been made in the last three decades in elucidating the disease pathogenesis, aided by the generation of animal and cellular models that have been instrumental in studying disease physiology. A review of the literature reveals that, up to now, no definitive pharmacological treatment for any CMT2A variant has been established; nonetheless, recent years have witnessed substantial progress. Many treatment approaches, especially concerning molecular therapy, such as histone deacetylase inhibitors, peptide therapy to increase mitochondrial fusion, the new therapeutic strategies based on MF1/MF2 balance, and SARM1 inhibitors, are currently in preclinical testing. The literature on gene silencing and gene replacement therapies is still limited, except for a recent study by Rizzo et al.(Rizzo et al., 2023), which recently first achieved encouraging results in in vitro and in vivo models of the disease. The near-future goal for these promising therapies is to progress to the stage of clinical translation.
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Doença de Charcot-Marie-Tooth , Animais , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/terapia , Doença de Charcot-Marie-Tooth/metabolismo , Mitocôndrias/metabolismo , GTP Fosfo-Hidrolases/genética , GTP Fosfo-Hidrolases/metabolismo , Fenótipo , Proteínas Mitocondriais/metabolismo , MutaçãoRESUMO
Mutations within immunoglobulin mu DNA binding protein (IGHMBP2), an RNA-DNA helicase, result in SMA with respiratory distress type I (SMARD1) and Charcot Marie Tooth type 2S (CMT2S). The underlying biochemical mechanism of IGHMBP2 is unknown as well as the functional significance of IGHMBP2 mutations in disease severity. Here we report the biochemical mechanisms of IGHMBP2 disease-causing mutations D565N and H924Y, and their potential impact on therapeutic strategies. The IGHMBP2-D565N mutation has been identified in SMARD1 patients, while the IGHMBP2-H924Y mutation has been identified in CMT2S patients. For the first time, we demonstrate a correlation between the altered IGHMBP2 biochemical activity associated with the D565N and H924Y mutations and disease severity and pathology in patients and our Ighmbp2 mouse models. We show that IGHMBP2 mutations that alter the association with activator of basal transcription (ABT1) impact the ATPase and helicase activities of IGHMBP2 and the association with the 47S pre-rRNA 5' external transcribed spacer. We demonstrate that the D565N mutation impairs IGHMBP2 ATPase and helicase activities consistent with disease pathology. The H924Y mutation alters IGHMBP2 activity to a lesser extent while maintaining association with ABT1. In the context of the compound heterozygous patient, we demonstrate that the total biochemical activity associated with IGHMBP2-D565N and IGHMBP2-H924Y proteins is improved over IGHMBP2-D565N alone. Importantly, we demonstrate that the efficacy of therapeutic applications may vary based on the underlying IGHMBP2 mutations and the relative biochemical activity of the mutant IGHMBP2 protein.
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Doença de Charcot-Marie-Tooth , Atrofia Muscular Espinal , Síndrome do Desconforto Respiratório do Recém-Nascido , Fatores de Transcrição , Camundongos , Animais , Humanos , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Mutação , Doença de Charcot-Marie-Tooth/genética , Adenosina Trifosfatases/genéticaRESUMO
Background: Pathogenic variants in the IGHMBP2 gene are associated with two distinct autosomal recessive neuromuscular disorders: spinal muscular atrophy with respiratory distress type 1 (SMARD1; OMIM #604320) and Charcot-Marie-Tooth type 2S (CMT2S; OMIM #616155). SMARD1 is a severe and fatal condition characterized by infantile-onset respiratory distress, diaphragmatic palsy, and distal muscular weakness, while CMT2S follows a milder clinical course, with slowly progressive distal muscle weakness and sensory loss, without manifestations of respiratory disorder. Methods: Whole-exome sequencing of the IGHMBP2 gene was performed for eight Vietnamese patients with IGHMBP2-related neuromuscular disorders including five patients with SMARD1 and the others with CMT2S. Results: We identified one novel IGHMBP2 variant c.1574T > C (p.Leu525Pro) in a SMARD1 patient. Besides that, two patients shared the same pathogenic variants (c.1235 + 3A > G/c.1334A > C) but presented completely different clinical courses: one with SMARD1 who deceased at 8 months of age, the other with CMT2S was alive at 3 years old without any respiratory distress. Conclusion: This study is the first to report IGHMBP-2-related neuromuscular disorders in Vietnam. A novel IGHMBP2 variant c.1574T > C (p.Leu525Pro) expressing SMARD1 phenotype was detected. The presence of three patients with the same genotype but distinct clinical outcomes suggested the interaction of variants and other factors including relating modified genes in the mechanism of various phenotypes.
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DHTKD1 is a nuclear gene that encodes "dehydrogenase E1 and transketolase domain-containing 1", essential in mitochondrial metabolism. First identified in the patients of 2-amino-apidic and 2 oxoapidic aciduria, mutation in this gene has recently been implicated in CMT2Q and ALS. Here we report the case of a septuagenarian who presented with a 2 years progressive history of respiratory and neck muscle weakness without significant bulbar and limb involvement. Clinical and electrophysiological examination revealed lower motor neuron involvement with widespread chronic denervation and reinnervation. Clinical exome sequencing revealed a heterozygous nonsense variant in exon 8 of the DHTKD1 gene, which was previously described in CMT2Q. This report highlights the pleotropic phenotypic presentation of DHTKD1 mutation and the need for genetic testing even in sporadic cases of ALS presenting at a later age.
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Esclerose Lateral Amiotrófica , Cetona Oxirredutases , Humanos , Cetona Oxirredutases/genética , Cetona Oxirredutases/metabolismo , Complexo Cetoglutarato Desidrogenase/genética , Complexo Cetoglutarato Desidrogenase/metabolismo , Esclerose Lateral Amiotrófica/diagnóstico , Esclerose Lateral Amiotrófica/genética , Esclerose Lateral Amiotrófica/metabolismo , Mutação/genética , MitocôndriasRESUMO
INTRODUCTION: Mutations in GDAP1 (Ganglioside-induced differentiation-associated protein 1) gene are linked to Charcot-Marie-Tooth disease (CMT), a Heterogenous group of disorders with multiple phenotypes, characterized by peripheral nerve dysfunction that can lead to vocal cord paralysis and diaphragmatic dysfunction. MAIN BODY: All three affected children of this chosen family have manifested the same clinical symptoms with progressive weakness, mild sensory impairment, and absent tendon reflexes in their early years. Electrodiagnostic analysis displayed an axonal type of neuropathy in affected patients. Sequencing of the GDAP1 gene was requested for all members of the family. Diagnostic assessments included pulmonary and vocal cord function tests, as well as phrenic and peripheral nerve conduction studies. Pathogenicity of GDAP1 variant p.Pro419Leu with axonal CMT2 and autosomal recessive inheritance was confirmed via in silico analysis. Patients with GDAP1 mutations showed dysphonia, speech difficulties, and the characteristic symptoms of CMT. The severity of symptoms correlated with the presence of a type of GDAP1 mutation. Patients with normal vocal cords and pulmonary function exhibited milder symptoms compared to those with GDAP1 mutations. Our study provides clinical insights into the phenotypic effects of GDAP1 mutations in CMT patients. The findings highlight the adverse clinical course and severe disability associated with GDAP1 mutations, including weak limb and laryngeal muscles. CONCLUSION: Patients with GDAP1 mutations and autosomal recessive neuropathy present with dysphonia and require interventions such as surgery, braces, physical therapy, and exercise. Early diagnosis and comprehensive clinical evaluations are crucial for managing CMT patients with GDAP1 mutations.
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Mitofusin-2 (MFN2) is an outer mitochondrial membrane protein essential for mitochondrial networking in most cells. Autosomal dominant mutations in the MFN2 gene cause Charcot-Marie-Tooth type 2A disease (CMT2A), a severe and disabling sensory-motor neuropathy that impacts the entire nervous system. Here, we propose a novel therapeutic strategy tailored to correcting the root genetic defect of CMT2A. Though mutant and wild-type MFN2 mRNA are inhibited by RNA interference (RNAi), the wild-type protein is restored by overexpressing cDNA encoding functional MFN2 modified to be resistant to RNAi. We tested this strategy in CMT2A patient-specific human induced pluripotent stem cell (iPSC)-differentiated motor neurons (MNs), demonstrating the correct silencing of endogenous MFN2 and replacement with an exogenous copy of the functional wild-type gene. This approach significantly rescues the CMT2A MN phenotype in vitro, stabilizing the altered axonal mitochondrial distribution and correcting abnormal mitophagic processes. The MFN2 molecular correction was also properly confirmed in vivo in the MitoCharc1 CMT2A transgenic mouse model after cerebrospinal fluid (CSF) delivery of the constructs into newborn mice using adeno-associated virus 9 (AAV9). Altogether, our data support the feasibility of a combined RNAi and gene therapy strategy for treating the broad spectrum of human diseases associated with MFN2 mutations.
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Doença de Charcot-Marie-Tooth , Células-Tronco Pluripotentes Induzidas , Humanos , Camundongos , Animais , Interferência de RNA , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , GTP Fosfo-Hidrolases/genética , GTP Fosfo-Hidrolases/metabolismo , Células-Tronco Pluripotentes Induzidas/metabolismo , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/terapia , Doença de Charcot-Marie-Tooth/metabolismo , Mutação , Hidrolases/genética , Camundongos TransgênicosRESUMO
BACKGROUND AND AIMS: Axonal forms of Charcot-Marie-Tooth disease (CMT) are classified as CMT2, distal hereditary motor neuropathy (dHMN) or hereditary sensory neuropathy (HSN) and can be caused by mutations in over 100 genes. We presently aimed to investigate for the first time the genetic landscape of axonal CMT in the Greek population. METHODS: Sixty index patients with CMT2, dHMN or HSN were screened by a combination of Sanger sequencing (GJB1) and next-generation sequencing custom-made gene panel covering 24 commonly mutated genes in axonal CMT. RESULTS: Overall, 20 variants classified as pathogenic or likely pathogenic were identified in heterozygous state in 20 index cases, representing 33.3% of the cohort. Of these, 14 were known pathogenic/likely pathogenic and six were designated as such according to ACMG classification, after in silico evaluation, testing for familial segregation and further literature review. The most frequently involved genes were GJB1 (11.7%), MPZ (5%) and MFN2 (5%), followed by DNM2 (3.3%) and LRSAM1 (3.3%). Single cases were identified with mutations in BSCL2, HSPB1 and GDAP1. INTERPRETATION: A wide phenotypic variability in terms of severity and age of onset was noted. Given the limited number of genes tested, the diagnostic yield of the present panel compares favourably with studies in other European populations. Our study delineates the genetic and phenotypic variability of inherited axonal neuropathies in the Greek population and contributes to the pathogenicity characterization of further variants linked to axonal neuropathies.
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Doença de Charcot-Marie-Tooth , Humanos , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/epidemiologia , Grécia , Mutação , Sequenciamento de Nucleotídeos em Larga Escala , Ubiquitina-Proteína Ligases/genéticaRESUMO
Mutations in ERLIN2 and MFN2 lead to the development of spastic paraplegia-18 (SPG18) and Charcot-Marie-Tooth type-2A (CMT2A), respectively. These disorders are unified by the fact that both can be termed inherited axonopathies. With whole-exome sequencing (WES), more patients of neurological disorders with clinical overlaps receive a genetic result than ever before. This study describes an Iranian family who harbor mutations in ERLIN2 and MFN2, simultaneously. The proband was a 73-year old man who has experienced weakness and spasticity of lower limbs since late childhood. He was diagnosed with hereditary spastic paraplegia (HSP). His WES identified a novel homozygous variant in ERLIN2 as well as a known heterozygous variant in MFN2. These variants were cosegregated with the phenotypes among the family members. His sister with a similar phenotype just carried the homozygous ERLIN2 variant, whereas, his asymptomatic brother and daughter carried the heterozygous variant of MFN2. Re-evaluation of the MFN2 variant carriers by nerve conduction study revealed that only the proband's daughter has peripheral neuropathy. Herein, using WES two distinct disease-causing variants with different modes of inheritance in ERLIN2 and MFN2 were detected in the proband. As expected, individuals with a defined MFN2 variant, p.Arg468His, were asymptomatic or had a mild phenotype. The co-occurrence of such diseases, SPG18 and CMT2A, may result in the milder phenotype to be overlooked or its features considered as a part of the symptoms of other disease. Certainly, providing genetic counseling in such cases can be challenging. These cases reveal the importance of WES.
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Dominant genetic variants in the mitofusin 2 (MFN2) gene lead to Charcot-Marie-Tooth type 2A (CMT2A), a neurodegenerative disease caused by genetic defects that directly damage axons. In this study, we reported a proband with a pathogenic variant in the GTPase domain of MFN2, c.494A > G (p.His165Arg). To date, at least 184 distinct MFN2 variants identified in 944 independent probands have been reported in 131 references. However, the field of medical genetics has long been challenged by how genetic variation in the MFN2 gene is associated with disease phenotypes. Here, by collating the MFN2 variant data and patient clinical information from Leiden Open Variant Database 3.0, NCBI clinvar database, and available related references in PubMed, we determined the mutation frequency, age of onset, sex ratio, and geographical distribution. Furthermore, the results of an analysis examining the relationship between variants and phenotypes from multiple genetic perspectives indicated that insertion and deletions (indels), copy number variants (CNVs), duplication variants, and nonsense mutations in single nucleotide variants (SNVs) tend to be pathogenic, and the results emphasized the importance of the GTPase domain to the structure and function of MFN2. Overall, three reliable classification methods of MFN2 genotype-phenotype associations provide insights into the prediction of CMT2A disease severity. Of course, there are still many MFN2 variants that have not been given clear clinical significance, which requires clinicians to make more accurate clinical diagnoses.
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Doença de Charcot-Marie-Tooth , Doenças Neurodegenerativas , Humanos , Mutação , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/patologia , GTP Fosfo-Hidrolases/genética , Estudos de Associação Genética , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/químicaRESUMO
Ubiquitin-dependent control of mitochondrial dynamics is important for protein quality and neuronal integrity. Mitofusins, mitochondrial fusion factors, can integrate cellular stress through their ubiquitylation, which is carried out by multiple E3 enzymes in response to many different stimuli. However, the molecular mechanisms that enable coordinated responses are largely unknown. Here we show that yeast Ufd2, a conserved ubiquitin chain-elongating E4 enzyme, is required for mitochondrial shape adjustments. Under various stresses, Ufd2 translocates to mitochondria and triggers mitofusin ubiquitylation. This elongates ubiquitin chains on mitofusin and promotes its proteasomal degradation, leading to mitochondrial fragmentation. Ufd2 and its human homologue UBE4B also target mitofusin mutants associated with Charcot-Marie-Tooth disease, a hereditary sensory and motor neuropathy characterized by progressive loss of the peripheral nerves. This underscores the pathophysiological importance of E4-mediated ubiquitylation in neurodegeneration. In summary, we identify E4-dependent mitochondrial stress adaptation by linking various metabolic processes to mitochondrial fusion and fission dynamics.
Assuntos
Mitocôndrias , Proteínas Mitocondriais , Ubiquitina-Proteína Ligases , Humanos , Aclimatação , Mitocôndrias/metabolismo , Saccharomyces cerevisiae/metabolismo , Ubiquitina , Ubiquitina-Proteína Ligases/metabolismo , Ubiquitinação , Proteínas Mitocondriais/metabolismoRESUMO
The hereditary neuropathies, collectively referred as Charcot-Marie-Tooth disease (CMT) and related disorders, are heterogeneous genetic peripheral nerve disorders that collectively comprise the commonest inherited neurological disease with an estimated prevalence of 1:2500 individuals. The field of hereditary neuropathies has made significant progress in recent years with respect to both gene discovery and treatment as a result of next-generation sequencing (NGS) approach. These investigations which have identified over 100 causative genes and new mutations have made the classification of CMT even more challenging. Despite so many different mutated genes, the majority of CMT forms share a similar clinical phenotype, and due to this phenotypic homogeneity, genetic testing in CMT is increasingly being performed through the use of NGS panels. The majority of patients still have a mutation in one the four most common genes (PMP22 duplication-CMT1A, MPZ-CMT1B, GJB1-CMTX1, and MFN2-CMT2A). This chapter focuses primarily on these four forms and their potential therapeutic approaches.
Assuntos
Doença de Charcot-Marie-Tooth , Humanos , Doença de Charcot-Marie-Tooth/diagnóstico , Doença de Charcot-Marie-Tooth/genética , Testes Genéticos , Mutação/genética , FenótipoRESUMO
Charcot-Marie-Tooth Disease (CMT) is a commonly inherited peripheral polyneuropathy. Clinical manifestations for this disease include symmetrical distal polyneuropathy, altered deep tendon reflexes, distal sensory loss, foot deformities, and gait abnormalities. Genetic mutations in heat shock proteins have been linked to CMT2. Specifically, mutations in the heat shock protein B1 (HSPB1) gene encoding for heat shock protein 27 (Hsp27) have been linked to CMT2F and distal hereditary motor and sensory neuropathy type 2B (dHMSN2B) subtype. The goal of the study was to examine the role of an endogenous mutation in HSPB1 in vivo and to define the effects of this mutation on motor function and pathology in a novel animal model. As sphingolipids have been implicated in hereditary and sensory neuropathies, we examined sphingolipid metabolism in central and peripheral nervous tissues in 3-month-old HspS139F mice. Though sphingolipid levels were not altered in sciatic nerves from HspS139F mice, ceramides and deoxyceramides, as well as sphingomyelins (SMs) were elevated in brain tissues from HspS139F mice. Histology was utilized to further characterize HspS139F mice. HspS139F mice exhibited no alterations to the expression and phosphorylation of neurofilaments, or in the expression of acetylated α-tubulin in the brain or sciatic nerve. Interestingly, HspS139F mice demonstrated cerebellar demyelination. Locomotor function, grip strength and gait were examined to define the role of HspS139F in the clinical phenotypes associated with CMT2F. Gait analysis revealed no differences between HspWT and HspS139F mice. However, both coordination and grip strength were decreased in 3-month-old HspS139F mice. Together these data suggest that the endogenous S139F mutation in HSPB1 may serve as a mouse model for hereditary and sensory neuropathies such as CMT2F.