Clinical and neurophysiological investigation of a large family with dominant Charcot-Marie-Tooth type 2 disease with pyramidal signs

Charcot-Marie-Tooth type 2A in vivo models: Current updates

Charcot-Marie-Tooth type 2A (CMT2A) is an inherited sensorimotor neuropathy associated with mutations within the Mitofusin 2 (MFN2) gene. These mutations impair normal mitochondrial functioning via different mechanisms, disturbing the equilibrium between mitochondrial fusion and fission, of mitophagy and mitochondrial axonal transport. Although CMT2A disease causes a significant disability, no resolutive treatment for CMT2A patients to date. In this context, reliable experimental models are essential to precisely dissect the molecular mechanisms of disease and to devise effective therapeutic strategies. The most commonly used models are either in vitro or in vivo, and among the latter murine models are by far the most versatile and popular. Here, we critically revised the most relevant literature focused on the experimental models, providing an update on the mammalian models of CMT2A developed to date. We highlighted the different phenotypic, histopathological and molecular characteristics, and their use in translational studies for bringing potential therapies from the bench to the bedside. In addition, we discussed limitations of these models and perspectives for future improvement.

The impact of pain and nocturnal cramps on sleep quality in Charcot Marie Tooth disease: a case-control study

Introduction

Charcot-Marie-Tooth disease is an inherited neuropathy that presents two main forms - type 1 and type 2 -, differentiated by the speed of the nervous conduction. Our goal was to assess sleep in Charcot-Marie-Tooth disease and its relationship with pain perception and nocturnal cramps.

Material and Methods

This was a case-control study. The case group was composed of 10 volunteers diagnosed with the type 1 and 23 with the type 2. The control group was composed of 22 individuals from the same family matched by age and gender. Volunteers underwent clinical screening to assess the presence of nocturnal cramps and filled the brief pain inventory, the Chalder fatigue scale, the Epworth sleepiness scale, and the Pittsburgh sleep quality index. Sleep was evaluated by actigraphy.

Results

Type 2 patients presented a more severe perception of pain and fatigue, more time spend awake after sleep onset, and had lower sleep efficiency. The individuals who reported nocturnal cramps also had worse perception of pain, reduced sleep latency, and increased sleep fragmentation.

Conclusion

The Charcot-Marie-Tooth type 2 was related with worse sleep quality, perception of pain, and fatigue and these parameters were negatively related.

Funktion und Struktur peripherer Nerven aus neuropädiatrischer Sicht: Wie klinische, neurophysiologische und Ultraschalluntersuchungen ergänzende diagnostische Informationen liefern

In der vorliegenden Übersicht wird dargestellt, wie sich klinisch neurophysiologische Methoden (Nervenleitgeschwindigkeit und Elektromyografie) und Ultraschalluntersuchungen (US) von peripheren Nerven bei der Abklärung von hereditären senso-motorischen Neuropathien (HMSN), der Friedreichschen Ataxie, erworbenen Neuropathien (am Beispiel von Diabetes mellitus) und traumatischen Nervenläsionen bei Kindern ergänzen können. Bei allen Formen der HMSN 1 kommt es zu einer Verlangsamung der Nervenleitgeschwindigkeit. Die Ultraschalluntersuchung zeigt nur bei HMSN1A eine deutlich vergrösserte Nervenquerschnittsfläche. Beim M. Friedreich können meist keine sensiblen Potentiale ausgelöst werden und die US-Resultate sind variabel. Bei traumatischen Nervenläsionen kann vor allem mithilfe der US-Untersuchung entschieden werden, ob eine operative Nervenrevision indiziert ist. Die erworbenen Neuropathien werden am Beispiel der diabetischen Neuropathie dargestellt. Die US- und die ENG Resultate sind oft abnorm, auch wenn klinisch keine Neuropathie-Symptome nachweisbar sind.

Metabolic and Functional Improvements in a Patient with Charcot-Marie-Tooth Disease Type 2 after EGCG Administration: A Case Report

Background and objectives: The aim of this study was to report a case of a patient with Charcot-Marie-Tooth disease type 2 (CMT2) treated with epigallocatechin gallate (EGCG) for 4 months in order to assess its therapeutic potential in CMT2. Materials and Methods: The study included a brother and a sister who have CMT2. The sister received 800 mg of EGCG for 4 months, while her brother received placebo for the same period of time. Both participants were assessed before and after daily administration by means of anthropometry; analysis of inflammatory and oxidation markers of interleukin-6 (IL-6) and paraoxonase 1 (PON1) in the blood sample; and motor tests: 2-min walk test (2MWT), 10-m walk test (10MWT), nine-hole peg test (9HPT) and handgrip strength measurement using a handheld Jamar dynamometer. Results: Regarding muscular and motor functions associated with higher inflammation and oxidation, improvements only observed in the woman in all analysed parameters (both biochemical and clinical associated with the metabolism and functionality) after 4 months of treatment with EGCG are noteworthy. Thus, this treatment is proposed as a good candidate to treat the disease.

Genetic mechanisms of peripheral nerve disease

Peripheral neuropathies of genetic etiology are a very diverse group of disorders manifesting either as non-syndromic inherited neuropathies without significant manifestations outside the peripheral nervous system, or as part of a systemic or syndromic genetic disorder. The former and most frequent group is collectively known as Charcot-Marie-Tooth disease (CMT), with prevalence as high as 1:2,500 world-wide, and has proven to be genetically highly heterogeneous. More than 100 different genes have been identified so far to cause various CMT forms, following all possible inheritance patterns. CMT causative genes belong to several common functional pathways that are essential for the integrity of the peripheral nerve. Their discovery has provided insights into the normal biology of axons and myelinating cells, and has highlighted the molecular mechanisms including both loss of function and gain of function effects, leading to peripheral nerve degeneration. Demyelinating neuropathies result from dysfunction of genes primarily affecting myelinating Schwann cells, while axonal neuropathies are caused by genes affecting mostly neurons and their long axons. Furthermore, mutation in genes expressed outside the nervous system, as in the case of inherited amyloid neuropathies, may cause peripheral neuropathy resulting from accumulation of β-structured amyloid fibrils in peripheral nerves in addition to various organs. Increasing insights into the molecular-genetic mechanisms have revealed potential therapeutic targets. These will enable the development of novel therapeutics for genetic neuropathies that remain, in their majority, without effective treatment.

Burst mitofusin activation reverses neuromuscular dysfunction in murine CMT2A

Charcot–Marie-Tooth disease type 2A (CMT2A) is an untreatable childhood peripheral neuropathy caused by mutations of the mitochondrial fusion protein, mitofusin (MFN) 2. Here, pharmacological activation of endogenous normal mitofusins overcame dominant inhibitory effects of CMT2A mutants in reprogrammed human patient motor neurons, reversing hallmark mitochondrial stasis and fragmentation independent of causal MFN2 mutation. In mice expressing human MFN2 T105M, intermittent mitofusin activation with a small molecule, MiM111, normalized CMT2A neuromuscular dysfunction, reversed pre-treatment axon and skeletal myocyte atrophy, and enhanced axon regrowth by increasing mitochondrial transport within peripheral axons and promoting in vivo mitochondrial localization to neuromuscular junctional synapses. MiM111-treated MFN2 T105M mouse neurons exhibited accelerated primary outgrowth and greater post-axotomy regrowth, linked to enhanced mitochondrial motility. MiM111 is the first pre-clinical candidate for CMT2A.

Charcot-Marie-Tooth disease type 2A is a rare genetic childhood disease where dying back of nerve cells leads to muscle loss in the arms and legs, causing permanent disability. There is no known treatment.

In this form of CMT, mutations in a protein called mitofusin 2 damage structures inside cells known as mitochondria. Mitochondria generate most of the chemical energy to power a cell, but when mitofusin 2 is mutated, the mitochondria are less healthy and are unable to move within the cell, depriving the cells of energy. This particularly causes problems in the long nerve cells that stretch from the spinal cord to the arm and leg muscles.

Now, Franco, Dang et al. wanted to see whether re-activating mitofusin 2 could correct the damage to the mitochondria and restore the nerve connections to the muscles. The researchers tested a new class of drug called a mitofusin activator on nerve cells grown in the laboratory after being taken from people suffering from CMT2A, and also from a mouse model of the disease. Mitofusin activators improved the structure, fitness and movement of mitochondria in both human and mice nerve cells. Franco, Dang et al. then tested the drug in the mice with a CMT2A mutation and found that it could also stimulate nerves to regrow and so reverse muscle loss and weakness.

This is the first time scientists have succeeded to reverse the effects of CMT2A in nerve cells of mice and humans. However, these drugs will still need to go through extensive testing in clinical trials before being made widely available to patients. If approved, mitofusin activators may also be beneficial for patients suffering from other genetic conditions that damage mitochondria.

Animal Models of CMT2A: State-of-art and Therapeutic Implications

Charcot-Marie-Tooth disease type 2A (CMT2A), arising from mitofusin 2 (MFN2) gene mutations, is the most common inherited axonal neuropathy affecting motor and sensory neurons. The cellular and molecular mechanisms by which MFN2 mutations determine neuronal degeneration are largely unclear. No effective treatment exists for CMT2A, which has a high degree of genetic/phenotypic heterogeneity. The identification of mutations in MFN2 has allowed the generation of diverse transgenic animal models, but to date, their ability to recapitulate the CMT2A phenotype is limited, precluding elucidation of its pathogenesis and discovery of therapeutic strategies. This review will critically present recent progress in in vivo CMT2A disease modeling, discoveries, drawbacks and limitations, current challenges, and key reflections to advance the field towards developing effective therapies for these patients.

Mitofusin 2 Dysfunction and Disease in Mice and Men

A causal relationship between Mitofusin (MFN) 2 gene mutations and the hereditary axonal neuropathy Charcot-Marie-Tooth disease type 2A (CMT2A) was described over 15 years ago. During the intervening period much has been learned about MFN2 functioning in mitochondrial fusion, calcium signaling, and quality control, and the consequences of these MFN2 activities on cell metabolism, fitness, and development. Nevertheless, the challenge of defining the central underlying mechanism(s) linking mitochondrial abnormalities to progressive dying-back of peripheral arm and leg nerves in CMT2A is largely unmet. Here, a different perspective of why, in humans, MFN2 dysfunction preferentially impacts peripheral nerves is provided based on recent insights into its role in determining whether individual mitochondria will be fusion-competent and retained within the cell, or are fusion-impaired, sequestered, and eliminated by mitophagy. Evidence for and against a regulatory role of mitofusins in mitochondrial transport is reviewed, nagging questions defined, and implications on mitochondrial fusion, quality control, and neuronal degeneration discussed. Finally, in the context of recently described mitofusin activating peptides and small molecules, an overview is provided of potential therapeutic applications for pharmacological enhancement of mitochondrial fusion and motility in CMT2A and other neurodegenerative conditions.

Evaluation of muscle strength, balance and functionality of individuals with type 2 Charcot-Marie-Tooth Disease

BACKGROUND

Charcot-Marie-Tooth (CMT) disease is part of a group of genetically determined neuropathies. The intrinsic muscles of the feet and legs are affected early in the disease, impacting balance and mobility.

RESEARCH QUESTION

The purpose of this study was to evaluate individuals with type 2 Charcot-Marie-Tooth disease to understand how motor changes interfere in balance and function.

METHODS

The sample comprised 15 individuals with CMT2 from the same family (CMT2G) and a control group (CG) of healthy individuals matched for age and gender. The CMT individuals were classified using the Charcot-Marie-Tooth Neuropathy Score (CMTNS). Muscle strength of the ankle was assessed using a manual dynamometer. Balance was measured using a stabilometer and Berg's Balance Scale (BBS). Functional performance was measured by the Timed Up and Go Test (TUG).

RESULTS

There was a statistically significant difference between the CMT2G and the CG for right side (RS) and left side (LS) muscle strength (dorsiflexors-RS and LS: p < 0,0001; invertors-RS and LS: p < 0.0001; plantarflexors-RS: p < 0.0001; plantarflexors-LS: p = 0.0019; evertors-RS: p = 0.0016; evertors-LS: p<0.0001) in the parameters for the velocity and displacement of center of pressure (CoP) anterior-posterior (AP) in the stabilometry tests with eyes open (EO) and closed (EC) (VCoPAP-EO and VCoPAP-EC: p = 0.0123; DCoPAP-OE: p = 0.0183 and DCoPAP-EC: p = 0.0129), the Berg Balance Scale (p = 0.0066) and the TUG test (p = 0.0003).

SIGNIFICANCE

Thus when the severity of the disease is mild the instability is caused by the weakness of the dorsiflexors and plantarflexors. In patients considered moderate/severe, in addition to weakness of the leg muscles, loss of proprioception will contribute to impaired balance.

Evaluation of Respiratory Muscle Strength and Pulmonary Function in Patients with Charcot-Marie-Tooth Disease Type 2

The aim of this study was to evaluate the pulmonary condition in a large family with Charcot-Marie-Tooth disease type 2 (CMT2). Eighteen participants diagnosed with CMT2 and 20 healthy individuals were evaluated by spirometry and maximal expiratory and maximal inspiratory pressures (MEP and MIP, respectively). Clinical disability was measured with CMT neuropathy score (CMTNS; range 0-36). One control group (CG) comprising 20 individuals, matched for age, sex and body mass index, were used for comparison. Eight patients were female (44.5%) and 10 patients were male (55.5%); mean age was 31.8 years (range 11-79) and CMTNS range was 6-26. Differences between CMT2 and CG in the spirometry and respiratory muscle strength were statistically significant for all dimensions. There were significant correlations between CMTNS and MIP (Pearson = -0.581) and MEP (Pearson = -0.5090). The results of this study show that patients with CMT, in spite of not showing clinical signs of advanced respiratory impairment, may present subclinical respiratory changes. The respiratory comprise in the CMT disease can be silent and insidious without presenting characteristic clinical signals.

MFN2-related neuropathies: Clinical features, molecular pathogenesis and therapeutic perspectives

Mitofusin 2 (MFN2) is a GTPase dynamin-like protein of the outer mitochondrial membrane, encoded in the nuclear genome by the MFN2 gene located on the short (p) arm of chromosome 1. MFN2 protein is involved in several intracellular pathways, but is mainly involved in a network that has an essential role in several mitochondrial functions, including fusion, axonal transport, interorganellar communication and mitophagy. Mutations in the gene encoding MFN2 are associated with Charcot-Marie-Tooth disease type 2A (CMT2A), a neurological disorder characterized by a wide clinical phenotype that involves the central and peripheral nervous system. Here, we present the clinical, genetic and neuropathological features of human diseases associated with MFN2 mutations. We also report proposed pathogenic mechanisms through which MFN2 mutations likely contribute to the development of neurodegeneration. MFN2-related disorders may occur more frequently than previously considered, and they may represent a paradigm for the study of the defective mitochondrial dynamics that seem to play a significant role in the molecular and cellular pathogenesis of common neurodegenerative diseases; thus they may also lead to the identification of related therapeutic targets.

Sleep pattern in Charcot-Marie-Tooth disease type 2: report of family case series

OBJECTIVES

Charcot-Marie-Tooth (CMT) disease is the most prevalent hereditary motor and sensory polyneuropathy, and a condition in which sleep has rarely been studied, particularly in relation to the type 2 (CMT2). Thus, we aimed to characterize the sleep patterns of a family affected by CMT2 disease.

METHODS

Sixteen volunteers with CMT2 from the same multigenerational family agreed to participate in the study (refusal rate = 31%). All participants answered sleep questionnaires and came to the sleep laboratory to perform a diagnostic polysomnography (PSG). Clinical manifestation and severity of the disease were also evaluated.

RESULTS

56% of the sample were male and 44% female, with a mean age of 32 ± 17 years, of normal weight (body mass index 21 ± 3 kg/m(2)); 64% presented moderate to severe CMT2. Regarding subjective sleep, 31% had excessive daytime sleepiness and 75% reported poor sleep quality. The PSG results revealed that CMT2 patients had an increase in stage N3 and a reduction in REM sleep, in addition to a high arousal index. Although 81% of the sample were snorers, only 13% had an apnea-hypopnea index (AHI) > 5. However, a positive correlation was found between the severity of disease and the AHI.

CONCLUSIONS

Taken together, these data show that CMT2 disease is characterized by important changes in sleep architecture, probably due to sleep fragmentation. Although these alterations may worsen with disease severity, it seems that they are not related to sleep breathing or movement disorders.

Immediate effects of using ankle-foot orthoses in the kinematics of gait and in the balance reactions in Charcot-Marie-Tooth disease

The Charcot-Marie-Tooth (CMT) disease is a peripheral hereditary neuropathy with progressive distal muscle atrophy and weakness, mainly in lower limbs, that evolves limiting the gait and balance. The objective of the study was to analyse the immediate effects of using Ankle-Foot Orthosis (AFO) in the gait's kinematics and balance in patients with CMT. Nine individuals were evaluated by Tinetti scales and Dynamic Gait Index (DGI) and gait's kinematics parameters through the motion capturing system. These evaluations were done before and during the use of AFO. Two-Way repeated analysis of variance was done to try the main or interaction effects related to "orthoses" and "repetition". A significant interaction effect was observed between the gait cycle and use the AFO to the average velocity (Wilks' Lambda=0.156, p=0.030, η2=0.844) like significant main effects in the ankle joint to the gait cycle (Wilks' Lambda=0.091, p=0.008, η2=0.909) and the use of AFO (Wilks' Lambda=0.444, p=0.013, η2=0.556). It was observed a significant change in the DGI scale during the use of AFO (p<0.05). The use of AFO promoted immediate effects on gait kinematics and in balance reactions. The results suggest that the use of AFO is an efficient strategy to stabilize the ankle joint, besides avoiding foot drop in patients with CMT.

Oral health, temporomandibular disorder, and masticatory performance in patients with Charcot-Marie-Tooth type 2

Background. The aim of this study was to evaluate the oral health status of temporomandibular disorders (TMD) and bruxism, as well as to measure masticatory performance of subjects with Charcot-Marie-Tooth type 2 (CMT2). Methods and Results. The average number of decayed, missing, and filled teeth (DMFT) for both groups, control (CG) and CMT2, was considered low (CG = 2.46; CMT2 = 1.85, P = 0.227). The OHIP-14 score was considered low (CG = 2.86, CMT2 = 5.83, P = 0.899). The prevalence of self-reported TMD was 33.3% and 38.9% (P = 0.718) in CG and CMT2 respectively and for self-reported bruxism was 4.8% (CG) and 22.2% (CMT2), without significant difference between groups (P = 0.162). The most common clinical sign of TMD was masseter (CG = 38.1%; CMT2 = 66.7%) and temporalis (CG = 19.0%; GCMT2 = 33.3%) muscle pain. The geometric mean diameter (GMD) was not significantly different between groups (CG = 4369; CMT2 = 4627, P = 0.157). Conclusion. We conclude that the CMT2 disease did not negatively have influence either on oral health status in the presence and severity of TMD and bruxism or on masticatory performance.