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Mutations in the small GTP-ase late endosomal protein RAB7 cause Charcot-Marie-Tooth type 2B neuropathy.

ABSTRACT: Charcot-Marie-Tooth type 2B (CMT2B) is clinically characterized by marked distal muscle weakness and wasting and a high frequency of foot ulcers, infections, and amputations of the toes because of recurrent infections. CMT2B maps to chromosome 3q13-q22. We refined the CMT2B locus to a 2.5-cM region and report two missense mutations (Leu129Phe and Val162Met) in the small GTP-ase late endosomal protein RAB7 which causes the CMT2B phenotype in three extended families and in three patients with a positive family history. The alignment of RAB7 orthologs shows that both missense mutations target highly conserved amino acid residues. RAB7 is ubiquitously expressed, and we found expression in sensory and motor neurons.

SUBMITTER: Verhoeven K

PROVIDER: S-EPMC1180247 | biostudies-literature | 2003 Mar

REPOSITORIES: biostudies-literature

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Mutations in the small GTP-ase late endosomal protein RAB7 cause Charcot-Marie-Tooth type 2B neuropathy.

Verhoeven Kristien K De Jonghe Peter P Coen Katrien K Verpoorten Nathalie N Auer-Grumbach Michaela M Kwon Jennifer M JM FitzPatrick David D Schmedding Eric E De Vriendt Els E Jacobs An A Van Gerwen Veerle V Wagner Klaus K Hartung Hans-Peter HP Timmerman Vincent V

American journal of human genetics 20030121 3

Charcot-Marie-Tooth type 2B (CMT2B) is clinically characterized by marked distal muscle weakness and wasting and a high frequency of foot ulcers, infections, and amputations of the toes because of recurrent infections. CMT2B maps to chromosome 3q13-q22. We refined the CMT2B locus to a 2.5-cM region and report two missense mutations (Leu129Phe and Val162Met) in the small GTP-ase late endosomal protein RAB7 which causes the CMT2B phenotype in three extended families and in three patients with a po ...[more]

PMID: 12545426

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Charcot Marie Tooth 2B Peripheral Sensory Neuropathy: How Rab7 Mutations Impact NGF Signaling?

Project description:Charcot-Marie-Tooth 2B peripheral sensory neuropathy (CMT2B) is a debilitating autosomal dominant hereditary sensory neuropathy. Patients with this disease lose pain sensation and frequently need amputation. Axonal dysfunction and degeneration of peripheral sensory neurons is a major clinical manifestation of CMT2B. However, the cellular and molecular pathogenic mechanisms remain undefined. CMT2B is caused by missense point mutations (L129F, K157N, N161T/I, V162M) in Rab7 GTPase. Strong evidence suggests that the Rab7 mutation(s) enhances the cellular levels of activated Rab7 proteins, thus resulting in increased lysosomal activity and autophagy. As a consequence, trafficking and signaling of neurotrophic factors such as nerve growth factor (NGF) in the long axons of peripheral sensory neurons are particularly vulnerable to premature degradation. A "gain of toxicity" model has, thus, been proposed based on these observations. However, studies of fly photo-sensory neurons indicate that the Rab7 mutation(s) causes a "loss of function", resulting in haploinsufficiency. In the review, we summarize experimental evidence for both hypotheses. We argue that better models (rodent animals and human neurons) of CMT2B are needed to precisely define the disease mechanisms.

| S-EPMC5343860 | biostudies-literature

Mitochondria dysfunction in Charcot Marie Tooth 2B Peripheral Sensory Neuropathy.

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Alteration of the late endocytic pathway in Charcot-Marie-Tooth type 2B disease.

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Project description:We have generated mouse models of real CMT1B mutations in the gene encoding for myelin protein zero (P0). One of these mutants, P0S63del is retained in the ER where it elicits an unfolded protein response (UPR). Genetic ablation of the UPR factor CHOP restores the motor capacity in S63del mice. We used microarray to decipher the molecular mechanism undelying the P0S63del neuropathy and the rescue in S63del/Chop null nerves. Sciatic nerves were dissected from WT, S63del, Chop null and S63del/Chop null mice at three different time points: (i) postnatal day 5 (P5) when myelination has just started and only the primary effects of the presence of the mutant protein should be detected; (ii) P28, around the peak of myelination, when all the downstream targets of CHOP should be activated; and (iii) 4 months, to check for secondary effects of the disease and because this was the time-point when the motor and morphological rescue due to the ablation of CHOP were clearly detectable.

2013-05-01 | E-GEOD-40610 | biostudies-arrayexpress

Clinical and genetic features of Charcot-Marie-Tooth disease 2F and hereditary motor neuropathy 2B in Japan.

Project description:Mutations in small heat shock protein beta-1 (HspB1) have been linked to Charcot-Marie-Tooth (CMT) disease type 2F and distal hereditary motor neuropathy type 2B. Only four cases with HSPB1 mutations have been reported to date in Japan. In this study between April 2007 and October 2014, we conducted gene panel sequencing in a case series of 1,030 patients with inherited peripheral neuropathies (IPNs) using DNA microarray, targeted resequencing, and whole-exome sequencing. We identified HSPB1 variants in 1.3% (13 of 1,030) of the patients with IPNs, who exhibited a male predominance. Based on neurological and electrophysiological findings, seven patients were diagnosed with CMT disease type 2F, whereas the remaining six patients were diagnosed with distal hereditary motor neuropathy type 2B. P39L, R127W, S135C, R140G, K141Q, T151I, and P182A mutations identified in 12 patients were described previously, whereas a novel K123* variant with unknown significance was found in 1 patient. Diabetes and impaired glucose tolerance were detected in 6 of the 13 patients. Our findings suggest that HSPB1 mutations result in two phenotypes of inherited neuropathies and extend the phenotypic spectrum of HSPB1-related disorders.

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SIRT2-knockdown rescues GARS-induced Charcot-Marie-Tooth neuropathy.

Project description:Charcot-Marie-Tooth disease is the most common inherited peripheral neuropathy. Dominant mutations in the glycyl-tRNA synthetase (GARS) gene cause peripheral nerve degeneration and lead to CMT disease type 2D. The underlying mechanisms of mutations in GARS (GARSCMT2D ) in disease pathogenesis are not fully understood. In this study, we report that wild-type GARS binds the NAD+ -dependent deacetylase SIRT2 and inhibits its deacetylation activity, resulting in the acetylated α-tubulin, the major substrate of SIRT2. The catalytic domain of GARS tightly interacts with SIRT2, which is the most CMT2D mutation localization. However, CMT2D mutations in GARS cannot inhibit SIRT2 deacetylation, which leads to a decrease of acetylated α-tubulin. Genetic reduction of SIRT2 in the Drosophila model rescues the GARS-induced axonal CMT neuropathy and extends the life span. Our findings demonstrate the pathogenic role of SIRT2-dependent α-tubulin deacetylation in mutant GARS-induced neuropathies and provide new perspectives for targeting SIRT2 as a potential therapy against hereditary axonopathies.

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Expression data from a Charcot-Marie-Tooth 1B neuropathy mouse model

2013-05-01 | GSE40610 | GEO

Rab7 mutants associated with Charcot-Marie-Tooth disease cause delayed growth factor receptor transport and altered endosomal and nuclear signaling.

Project description:Rab7 belongs to the Ras superfamily of small GTPases and is a master regulator of early to late endocytic membrane transport. Four missense mutations in the late endosomal Rab7 GTPase (L129F, K157N, N161T, and V162M) cause the autosomal dominant peripheral neuropathy Charcot-Marie-Tooth type 2B (CMT2B) disease. As yet, the pathological mechanisms connecting mutant Rab7 protein expression to altered neuronal function are undefined. Here, we analyze the effects of Rab7 CMT2B mutants on epidermal growth factor (EGF)-dependent intracellular signaling and trafficking. Three different cell lines expressing Rab7 CMT2B mutants and stimulated with EGF exhibited delayed trafficking of EGF to LAMP1-positive late endosomes and lysosomes and slowed EGF receptor (EGFR) degradation. Expression of all Rab7 CMT2B mutants altered the Rab7 activation cycle, leading to enhanced and prolonged EGFR signaling as well as variable increases in p38 and ERK1/2 activation. However, due to reduced nuclear translocation of p38 and ERK1/2, the downstream nuclear activation of Elk-1 was decreased along with the expression of immediate early genes like c-fos and Egr-1 by the disease mutants. In conclusion, our results demonstrate that Rab7 CMT2B mutants impair growth factor receptor trafficking and, in turn, alter p38 and ERK1/2 signaling from perinuclear, clustered signaling endosomes. The resulting down-regulation of EGFR-dependent nuclear transcription that is crucial for normal axon outgrowth and peripheral innervation offers a crucial new mechanistic insight into disease pathogenesis that is relevant to other neurodegenerative diseases.

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Sphingosine 1-phosphate lyase deficiency causes Charcot-Marie-Tooth neuropathy.

Project description:ObjectiveTo identify the unknown genetic cause in a nuclear family with an axonal form of peripheral neuropathy and atypical disease course.MethodsDetailed neurologic, electrophysiologic, and neuropathologic examinations of the patients were performed. Whole exome sequencing of both affected individuals was done. The effect of the identified sequence variations was investigated at cDNA and protein level in patient-derived lymphoblasts. The plasma sphingoid base profile was analyzed. Functional consequences of neuron-specific downregulation of the gene were studied in Drosophila.ResultsBoth patients present an atypical form of axonal peripheral neuropathy, characterized by acute or subacute onset and episodes of recurrent mononeuropathy. We identified compound heterozygous mutations cosegregating with disease and absent in controls in the SGPL1 gene, encoding sphingosine 1-phosphate lyase (SPL). The p.Ser361* mutation triggers nonsense-mediated mRNA decay. The missense p.Ile184Thr mutation causes partial protein degradation. The plasma levels of sphingosine 1-phosphate and sphingosine/sphinganine ratio were increased in the patients. Neuron-specific downregulation of the Drosophila orthologue impaired the morphology of the neuromuscular junction and caused progressive degeneration of the chemosensory neurons innervating the wing margin bristles.ConclusionsWe suggest SPL deficiency as a cause of a distinct form of Charcot-Marie-Tooth disease in humans, thus extending the currently recognized clinical and genetic spectrum of inherited peripheral neuropathies. Our data emphasize the importance of sphingolipid metabolism for neuronal function.

| S-EPMC5304460 | biostudies-literature

AAV1.NT-3 gene therapy for charcot-marie-tooth neuropathy.

Project description:Charcot-Marie-Tooth (CMT) neuropathies represent a heterogeneous group of peripheral nerve disorders affecting 1 in 2,500 persons. One variant, CMT1A, is a primary Schwann cell (SC) disorder, and represents the single most common variant. In previous studies, we showed that neurotrophin-3 (NT-3) improved the trembler(J) (Tr(J)) mouse and also showed efficacy in CMT1A patients. Long-term treatment with NT-3 was not possible related to its short half-life and lack of availability. This led to considerations of NT-3 gene therapy via adenoassociated virus (AAV) delivery to muscle, acting as secretory organ for widespread distribution of this neurotrophic agent. In the Tr(J) model of demyelinating CMT, rAAV1.NT-3 therapy resulted in measurable NT-3 secretion levels in blood sufficient to provide improvement in motor function, histopathology, and electrophysiology of peripheral nerves. Furthermore, we showed that the compound muscle action potential amplitude can be used as surrogate for functional improvement and established the therapeutic dose and a preferential muscle-specific promoter to achieve sustained NT-3 levels. These studies of intramuscular (i.m.) delivery of rAAV1.NT-3 serve as a template for future CMT1A clinical trials with a potential to extend treatment to other nerve diseases with impaired nerve regeneration.

| S-EPMC3944324 | biostudies-literature

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