Charcot-Marie-Tooth Type Research Articles

Charcot–Marie–Tooth disease-associated mutant tRNA synthetases linked to altered dimer interface and neurite distribution defect

Charcot-Marie-Tooth (CMT) diseases are the most common heritable peripheral neuropathy. At least 10 different mutant alleles of GARS (the gene for glycyl-tRNA synthetase) have been reported to cause a dominant axonal form of CMT (type 2D). A unifying connection between these mutations and CMT has been unclear. Here, mapping mutations onto the recently determined crystal structure of human GlyRS showed them within a band encompassing both sides of the dimer interface, with two CMT-causing mutations being at sites that are complementary partners of a "kissing" contact across the dimer interface. The CMT phenotype is shown here to not correlate with aminoacylation activity. However, most mutations affect dimer formation (to enhance or weaken). Seven CMT-causing variants and the wild-type protein were expressed in transfected neuroblastoma cells that sprout primitive neurites. Wild-type GlyRS distributed into the nascent neurites and was associated with normal neurite sprouting. In contrast, all mutant proteins were distribution-defective. Thus, CMT-causing mutations of GlyRS share a common defect in localization. This defect may be connected in some way to a change in the surfaces at the dimer interface.

Mitochondrial coupling defect in Charcot–Marie–Tooth type 2A disease

Mutations of the mitofusin 2 gene (MFN2) may account for at least a third of the cases of Charcot-Marie-Tooth disease type 2 (CMT2). This study investigates mitochondrial cellular bioenergetics in MFN2-related CMT2A. Mitochondrial network morphology and metabolism were studied in cultures of skin fibroblasts obtained from four CMT2A patients harboring novel missense mutations of the MFN2 gene. Although the mitochondrial network appeared morphologically unaltered, there was a significant defect of mitochondrial coupling associated with a reduction of the mitochondrial membrane potential. Our results suggest that the sharply reduced efficacy of oxidative phosphorylation in MFN2-related CMT2A may contribute to the pathophysiology of the axonal neuropathy.

Altered Axonal Mitochondrial Transport in the Pathogenesis of Charcot-Marie-Tooth Disease from Mitofusin 2 Mutations

Mutations in the mitochondrial fusion protein mitofusin 2 (MFN2) are the most commonly identified cause of Charcot-Marie-Tooth type 2 (CMT2), a dominantly inherited disease characterized by degeneration of peripheral sensory and motor axons. However, the mechanism by which mutations in this ubiquitously expressed mitochondrial fusion protein lead to neuropathy has not yet been elucidated. To explore how MFN2 mutations lead to degeneration of peripheral axons, we expressed neuropathy-associated forms of MFN2 in cultured dorsal root ganglion neurons, cells preferentially affected in CMT2. Disease-associated MFN2 mutant proteins induced abnormal clustering of small fragmented mitochondria in both neuronal cell bodies and proximal axons. Interestingly, transport of mitochondria in axons was significantly impaired in neurons expressing disease-mutated forms of MFN2. The diminished axonal mitochondrial transport was not attributable to diminished ATP levels in the neurons, and oxidative respiration was normal in mutant MFN2-expressing cells. Additionally, mitochondrial oxidative enzyme activity was normal in muscle mitochondria from a CMT2 patient with an MFN2 mutation, further supporting that abnormal mitochondrial transport in neurons is independent from an energy production defect. This abnormal mitochondrial trafficking provides a likely explanation for the selective susceptibility of the longest peripheral axons to MFN2 mutations, in which proper localization of mitochondria is critical for axonal and synaptic function.

Variables influencing quality of life and disability in Charcot Marie Tooth (CMT) patients: Italian multicentre study

The purpose of this study was to assess the variables that influence quality of life (QoL) and disability in patients with Charcot-Marie-Tooth disease (CMT). We performed a prospective multicentre study using validated clinical disability and QoL measurements. Multivariate analysis was performed using QoL as a dependent variable and duration of symptoms, age, gender and CMT type, depression and disability measurements as independent variables. We enrolled 211 patients. QoL was highly significantly deteriorated with respect to the Italian normative sample. The physical aspect of QoL was mainly related to disability but it does not increase with the age, probably because of an adaptation between expectation and reality. The mental QoL is influenced by depression (hence we have to consider this aspect approaching CMT patients). Moreover, we observed that women complained of more severe symptoms than men. Finally, some CMT subtypes are related to more severe bodily pain symptoms than others. Multiperspective assessment of CMT showed new aspects of this disease, mainly regarding (1) differences between men and women and (2) the crucial role of pain and depression.

Charcot-Marie-Tooth disease type 2E, a disorder of the cytoskeleton

The neurofilament light chain (NF-L) is a major constituent of intermediate filaments and plays a pivotal function in the assembly and maintenance of axonal cytoskeleton. Mutations in the NF-L gene (NEFL) cause autosomal dominant neuropathies that are classified either as axonal Charcot-Marie-Tooth (CMT) type 2E (CMT2E) or demyelinating CMT type 1F (CMT1F). The pathophysiological bases of the disorder(s) are elusive. We performed a mutational analysis of NEFL in a series of 177 index cases with CMT and without mutations in the genes for peripheral myelin protein zero (MPZ), peripheral myelin protein 22 (PMP22) and connexin 32 (GJB1); the motor nerve conduction velocity (MNCV) at the median nerve was below 38 m/s in 76 cases and above 38 m/s in 101. We identified five new pedigrees with four mutations in the head and rod domains of NF-L, including a novel Leu268Pro substitution and a novel del322Cys_326Asn deletion. Several examined affected members exhibited marked variability in the severity of disease and age at onset. Nerve conduction alterations were consistent with an axonal neuropathy often associated with demyelinating features, such as prolonged distal latencies (DL). Pathological examination of sural nerve biopsies in the probands detected in four cases a chronic axonal neuropathy dominated by focal accumulations of NF with axonal swellings (giant axons) and significant secondary demyelination; in the fifth case no NFs accumulations were evident but many myelinated fibres consisted exclusively of microtubules with few or absent NF. The pathological phenotype correlated with the pattern of nerve conduction alterations and indicated that NEFL mutations cause a profound alteration of the cytoskeleton possibly related to defective targeting of NF.

N.P.3 04 A novel Pro105Thr mutation in the MPZ gene causes late onset CMT2 disease with hearing impairment

Only 10% of mutations in the Myelin Protein Zero (MPZ) gene are associated with Charcot-Marie-Tooth type 2 (CMT2) disease. The phenotype of CMT2 disease caused by mutations in the MPZ gene is usually characterized by late onset (over 4th decade), marked sensory disturbances, pupillary abnormalities and hearing loss (observed in some patients). MPZ gene analysis in AD CMT2 family basing upon clinical features. Neurological examination, electrophysiological study, audiometry and molecular genetic analysis of the MPZ gene.

P13.1 Conduction block in Charcot–Marie–Tooth type 1B (CMT1B) neuropathy

Background: On neurophysiological studies the hereditary demyelinating motor and sensory neuropathies (CMT1) usually show uniform reduction in motor conduction velocities. On the other hand, conduction block (CB) far from compression sites is typical of acquired demyelinating neuropathies. Aims: To describe a patient with CMT1 in whom neurophysiological studies disclosed marked CB outside entrapment sites. Case report:A34-year-oldwomanwith afive-year history ofmuscle cramps, right hand and distal lower limbweakness after longstanding efforts. She only startedwalking at the age of 30months but had no other motor development problem. Her father had a history of disabling demyelinating motor– sensory neuropathy. On neurological examination, she had bilateral pes cavus, slight weakness on right thumb abduction, bilateral foot dorsiflexion and hallux extension weakness (4/5); there was a generalized areflexia and distal lower limb light touch and pinprick hypostesia and few errors on postural sense testing; walking on heels was impaired. Motor conduction studies showed low velocities with prolonged latencies, with absent motor responses in feet. Partial conduction blocks were present in the median and ulnar nerves at the forearm (below elbow), more severe aftermuscular fatigue. Sensory potentialswere absent (lower limbs) or small. Laboratorial evaluation includingCSFanalysis was unremarkable. The genetic study was positive for the 233C > T mutation at the MPZ gene. Conclusion: This case illustrates the electrophysiological heterogeneity of CMT1B and adds this entity to conduction block differential diagnosis.

TP2.4 A 5-year natural history study in Charcot–Marie–Tooth type 1A patients

TP2.4 A 5-year natural history study in Charcot–Marie–Tooth type 1A patients

TP2.2 Charcot–Marie–Tooth type 1a: Correlation between neurophysiological pattern and quality of life

TP2.2 Charcot–Marie–Tooth type 1a: Correlation between neurophysiological pattern and quality of life

MFN2 mutation distribution and genotype/phenotype correlation in Charcot-Marie-Tooth type 2

Mutations in mitofusin 2 (MFN2) have been reported in Charcot-Marie-Tooth type 2 (CMT2) families. To study the distribution of mutations in MFN2 we screened 323 families and isolated patients with distinct CMT phenotypes. In 29 probands, we identified 22 distinct MFN2 mutations, and 14 of these mutations have not been reported before. All mutations were located in the cytoplasmic domains of the MFN2 protein. Patients presented with a classical but rather severe CMT phenotype, since 28% of them were wheelchair-dependent. Some had additional features as optic atrophy. Most patients had an early onset and severe disease status, whereas a smaller group experienced a later onset and milder disease course. Electrophysiological data showed in the majority of patients normal to slightly reduced nerve conduction velocities with often severely reduced amplitudes of the compound motor and sensory nerve action potentials. Examination of sural nerve specimens showed loss of large myelinated fibres and degenerative mitochondrial changes. In patients with a documented family history of CMT2 the frequency of MFN2 mutations was 33% indicating that MFN2 mutations are a major cause in this population.

Charcot–Marie–Tooth type 4F disease caused by S399fsx410 mutation in the PRX gene

Charcot-Marie-Tooth type 4F disease (CMT4F) is an autosomal recessive neuropathy caused by mutations in the PRX gene. To date, only seven mutations have been identified in the PRX gene. In this study, the authors report a novel S399fsX410 mutation in the PRX gene and its effects at the protein level, which was identified in an 8-year-old patient with early-onset CMT disease.

Intermediate forms of Charcot-Marie-Tooth neuropathy

The Charcot-Marie-Tooth (CMT) neuropathies divide into two main electrophysiological groups with slow and near normal conduction velocities corresponding to Schwann cell and axonal pathology. An intermediate group also exists with nerve conduction velocities, which overlaps the two main groups. Families with intermediate CMT can be recognized in which different affected individuals in the same family have motor conduction velocities in both the CMT type 1 and 2 ranges (i.e., above and below 38 m/s). The intermediate group is caused by a limited number of distinct gene mutations in dynamin2 (DNM2), gap-junction protein 1 (GJB1), neurofilament light polypeptide (NF-L) genes, and a rare mutation and as yet unknown genes on chromosome 1 and 10 loci. Intermediate forms of CMT may be associated with unique disease mechanisms affecting both Schwann cells and axons. It is useful to recognize this unique group of neuropathies for diagnostic and management purposes.

Role of immune cells in animal models for inherited peripheral neuropathies

Mice expressing half of the normal dose of protein zero (P0+/- mice) or completely deficient gap-junction protein connexin 32 -/- mice mimic demyelinating forms of inherited neuropathies, such as Charcot-Marie-Tooth (CMT) neuropathies type 1B and CMT type 1X, respectively. In both models, an almost normal myelin formation is observed during the first months of life, followed by a slowly progressing demyelinating neuropathy. In both models, there is a substantial increase of CD8+ T-lymphocytes and macrophages within the demyelinating nerves. Recently, this has also been observed in mice mildly overexpressing human peripheral myelin protein 22 kD mimicking the most common form of CMT, CMT type 1A. In all demyelinating models, the macrophages show close contacts with intact myelin sheaths or demyelinated axons, suggesting an active role of these cells in myelin degeneration. Additionally, fibroblast-like cells contact macrophages, suggesting a functional role of fibroblast-like cells in macrophage activation. By cross-breeding P0+/- and gap-junction protein connexin 32-/- mice with immunodeficient recombination activating gene-1-deficient mutants, a substantial alleviation of the demyelinating phenotype was observed. Similarly, cross-breeding of P0+/- mice with mutants with a defect in macrophage activation led to an alleviated phenotype as well. These findings demonstrate that the immune system is involved in the pathogenesis of demyelinating neuropathies. In contrast, in P0-/- mice, which display a compromised myelin compaction and axonal loss from onset, immune cells appear to have a neuroprotective effect because cross-breeding with recombination activating gene-1 mutants leads to an aggravation of axonopathic changes. In the present review, we discuss the influence of the immune system on inherited de- and dysmyelination regarding disease mechanisms and possible clinical implications.

Axonal damage and demyelination in long‐term dorsal root ganglia cultures from a rat model of Charcot–Marie–Tooth type 1A disease

Clinical progression in hereditary and acquired demyelinating disorders of both the central and peripheral nervous system is mainly due to a time-dependent axonal impairment. We established 90-day dorsal root ganglia (DRG) cultures from a rat model of Charcot-Marie-Tooth type 1A (CMT1A) neuropathy to evaluate the structure of myelin and axons, and the expression of myelin-related proteins and cytoskeletal components, by morphological and molecular techniques. Both wild-type and CMT1A cultures were rich in myelinated fibres. Affected cultures showed dysmyelinated internodes and focal myelin swellings. Furthermore, uncompacted myelin and smaller axons with increased neurofilament (NF) density were found by electron microscopy, and Western blots showed higher levels of nonphosphorylated NF. Confocal microscopy demonstrated an abnormal distribution of the myelin-associated glycoprotein which, instead of being expressed at the noncompact myelin level, showed focal accumulation along the internodes while other myelin proteins were normally distributed. These findings suggest that CMT1A DRG cultures, similarly to the animal model and human disease, undergo axonal atrophy over a period of time. This model may be utilized to study the molecular changes underlying demyelination and secondary axonal impairment. As axonal damage may occur after just 3 months and tissue cultures represent a strictly controlled environment, this model may be ideal for testing neuroprotective therapies.

Axonal neuropathy with optic atrophy is caused by mutations in mitofusin 2

Charcot-Marie-Tooth (CMT) neuropathy with visual impairment due to optic atrophy has been designated as hereditary motor and sensory neuropathy type VI (HMSN VI). Reports of affected families have indicated autosomal dominant and recessive forms, but the genetic cause of this disease has remained elusive. Here, we describe six HMSN VI families with a subacute onset of optic atrophy and subsequent slow recovery of visual acuity in 60% of the patients. Detailed clinical and genetic studies were performed. In each pedigree, we identified a unique mutation in the gene mitofusin 2 (MFN2). In three families, the MFN2 mutation occurred de novo; in two families the mutation was subsequently transmitted from father to son indicating autosomal dominant inheritance. MFN2 is a mitochondrial membrane protein that was recently reported to cause axonal CMT type 2A. It is intriguing that MFN2 shows functional overlap with optic atrophy 1 (OPA1), the protein underlying the most common form of autosomal dominant optic atrophy, and mitochondrial encoded oxidative phosphorylation components as seen in Leber's hereditary optic atrophy. We conclude that autosomal dominant HMSN VI is caused by mutations in MFN2, emphasizing the important role of mitochondrial function for both optic atrophies and peripheral neuropathies.

Ｃｈａｒｃｏｔ‐Ｍａｒｉｅ‐Ｔｏｏｔｈ病の眼球運動について

Charcot-Marie Tooth (CMT) diseases is a clinically and genetically heterogeneous group of peripheral nerve disorders characterized by distal muscle weakness and atrophy. There have been some reports of CMT diseases with CNS involvement, especially cerebellar atrophy. Recently, families with CMT type muscular atrophy with cerebellar ataxia have been increasingly reported, and it has been proposed as a new disease entity. However, the pathogenesis of CMT diseases with CNS involvement is unknown.We reported eye moments recorded electro-oculographically in seven patients with Charcot-Marie Tooth diseases. Brain MRI demonstrated slight cerebellar atrophy in only one case and no apparent abnormality in the other six cases.No abnormal eye movement was found in two patients with CMT type 1, but some abnormal eye movements were surprisingly observed in five patients including one with CMT type 1, three with CMT type 2, and one with HNPP. The observed eye movement abnormalities were lateral-gazed nystagmus in 2 patients, impaired smooth pursuit in 5 patients, saccadic hypometria in 3 patients, and a decrease of saccadic velocity in 2 patients. In all 5 patients, decreases in the slow phase of OKN and of visual suppression on the caloric test were observed. From eye movements, three cases were diagnosed as cerebellar involvement, one as cerebellar and brain stem involvements, and one as suspicious cerebellar deficit. One patient with CMT type 1 showing cerebellar and brain stem involvements and abnormal eye movement was genetically diagnosed as CMT 1A, which is the most common form of CMT disease.The findings suggest that CMT disease with cerebellar or brain stem involvement is more frequent than has been previously reported. Further investigation is necessary on eye movement abnormalities in patients with CMT disease. Examination of eye movement was a very useful and sensitive indicator in the screening of CMT patients to evaluate any central nervous deficit, especially concerning cerebellar and brainstem involvements.

Charcot-Marie-Tooth disease: Correction of the CMT-1A phenotype

Charcot-Marie-Tooth (CMT) disease constitutes a group of prevalent hereditary, chronic and debilitating peripheral neuropathies. CMT type 1A (CMT-1A), the most common form of CMT, is autosomal dominant and is characterized by peripheral demyelination. No pharmacotherapies currently exist for CMT-1A, although identification of an underlying duplication in the gene for PMP22 (peripheral myelin protein 22), a glycoprotein expressed in myelin, has ignited the search for candidates to correct the CMT-1A phenotype. To date, these include the progesterone antagonist onapristone, the antioxidant ascorbic acid and the natural neurotrophic factor neurotrophin-3.

A LARGE FAMILY WITH CHARCOT-MARIE-TOOTH TYPE 1A AND TYPE 2 DIABETES MELLITUS

Charcot-Marie-Tooth (CMT) disease is a hereditary demyelinating peripheral neuropathy, and CMT Type 1A is the most common form. In most cases, CMT1A is usually caused by duplication at chromosome 17p11.2–12. Type 2 diabetes mellitus (Type 2 DM) is a common metabolic disorder, characterized by chronic hyperglycemia that can be associated with micro- and/or macrovascular complications. Only a few studies reported CMT1A duplication in association with Type 2 DM. This article explores the characteristics of a large family of 69 members with respect to CMT1A and Type 2 DM. CMT1A was detected in 28 of them. Molecular genetic study was performed in 22, and duplication was detected in all of them. Six of the 22 members with CMT1A also had Type 2 DM based on the American Diabetes Association diagnostic criteria. Association of these two conditions may be coincidental; however, the occurence of these two diseases in this large family may also suggest a genetic basis. More extensive reports and further investigations of such families having this combination will certainly provide a better understanding of this link.

A novel Met116Thr mutation in the GDAP1 gene in a Polish family with the axonal recessive Charcot–Marie–Tooth type 4 disease

Mutations in the gene coding for ganglioside-induced differentiation-associated protein-1 (GDAP1), which maps to chromosome 8q21, have been described in families with autosomal recessive Charcot–Marie–Tooth disease (CMT4A). Interestingly, some mutations in the GDAP1 gene have been reported in the demyelinating form of CMT1 disease, whereas others were found in patients with the axonal type of CMT disease. So far, 23 mutations in the GDAP1 gene have been reported in patients of different ethnic origins. In this study we report a novel mutation Met116Thr in the GDAP1 gene identified in a three generation Polish family with axonal CMT4.

Onset and duration of mivacurium‐induced neuromuscular blockade in children with Charcot–Marie–Tooth disease. A case series with five children

The Charcot-Marie-Tooth (CMT) disorders are a group of hereditary motor and sensory neuropathies characterized clinically by peripheral muscle wasting and weakness. We hypothesized that unknown involvement of the muscle used for monitoring neuromuscular block may account for the conflicting reports about the effect of nondepolarizing neuromuscular agents in these patients. The aim of this study was to compare onset and recovery from mivacurium-induced neuromuscular block on the adductor pollicis and orbicularis oculi muscles. We used mivacurium 0.2 mg.kg(-1) in five children (aged 7-12 years) with CMT type I undergoing propofol-fentanyl-oxygen-air anesthesia for orthopedic surgery. Using acceleromyography, neuromuscular transmission was monitored in parallel in the eye and thumb muscles, and onset and duration times were recorded. Following bolus administration of 0.2 mg.kg(-1) of mivacurium the onset time ranged between 135 and 240 s and 75 and 165 s in the eye and in the thumb, respectively. The recovery time varied between 5.3 and 16 min and 6 and 31.3 min in the eye and in the thumb, respectively. In our small series of patients with CMT the clinical duration of mivacurium-induced neuromuscular block was similar to data known from children without neuromuscular disease.