Diagnosis, natural history, and management of Charcot–Marie–Tooth disease

Quantifying gait impairment in individuals affected by Charcot-Marie-Tooth disease: the usefulness of gait profile score and gait variable score

Background: Gait analysis is a reliable tool to characterise ambulation in Charcot-Marie-Tooth, the obtained are complex data makes its use scarce in clinical practice. The use of synthetic measures may enable the clinician to easily interpret gait kinematics in Charcot-Marie-Tooth.Aims: To test the usefulness of Gait Profile Score as a method to quantify and monitor kinematic gait alterations in Charcot-Marie-Tooth.Methods: A group of patients with Charcot-Marie-Tooth and a control group underwent Gait Analysis. Neurological impairment was evaluated by means of the Charcot Marie Tooth neuropathy score in his original form and in the Rasch Analysis revised form. Differences in Kinematics scores induced by the pathology were assessed using the Mann-Whitney U test. The relationship between gait parameters and Charcot Marie Tooth neuropathy score was assessed by means of the Spearman correlation.Results: Twenty patients were enrolled. Mann-Whitney U test revealed a significant effect of the pathology on Gait Profile Score (p < 0.001). Charcot Marie Tooth neuropathy score was positively correlated with Gait Profile Score (Rho = 0.708, p = 0.001).Conclusion: Gait profile score can differentiate Charcot Marie Tooth from unaffected people and to quantify ambulation impairment, also identifying the joints more affected by the disease.Implications for rehabilitationPhysiotherapy and orthotics constitute the sole possible clinical approach for Charcot Marie Tooth, but the clinical scales are scarcely effective for assessing the rehabilitative outcome.Synthetic measures are able to summarize Charcot Marie tooth kinematics in a single score, and Gait Profile Score is able to differentiate patients with Charcot Marie tooth from healthy controls.Gait Profile Score is related to clinical disability as measured by the Charcot Marie tooth neuropathy score.

Juvenile-onset polyneuropathy in American Staffordshire Terriers

BACKGROUND

The only hereditary neurologic disorder described so far in American Staffordshire Terriers is adult-onset cerebellar degeneration secondary to ceroid lipofuscinosis. We have seen several dogs with a newly recognized neurological disease characterized by locomotor weakness with or without respiratory signs and juvenile onset consistent with degenerative polyneuropathy of genetic origin.

OBJECTIVES

To characterize a novel polyneuropathy in juvenile American Staffordshire Terriers.

ANIMALS

Fourteen American Staffordshire Terriers presented with clinical signs consistent with juvenile-onset polyneuropathy at 5 veterinary hospitals between May 2005 and July 2017.

METHODS

Case series. Dogs were included retrospectively after a diagnosis of degenerative polyneuropathy had been confirmed by nerve biopsy. Clinical, pathological, electrophysiological, histological data, and outcome were reviewed and a pedigree analysis performed.

RESULTS

All dogs displayed clinical signs of neuromuscular disease with generalized motor and sensory involvement, associated with focal signs of laryngeal paralysis (10/14 dogs) and megaesophagus (1/14 dogs). Histopathological findings were consistent with degenerative polyneuropathy. Follow-up was available for 11 dogs, and 3 dogs were euthanized shortly after diagnosis. In these 11 dogs, the disease was slowly progressive and the animals maintained good quality of life with ability to walk. Pedigree analysis was mostly consistent with an autosomal recessive mode of inheritance.

CONCLUSIONS AND CLINICAL IMPORTANCE

Juvenile polyneuropathy, associated with laryngeal paralysis, is a newly described entity in American Staffordshire Terriers, and results from degenerative neuropathy. When surgery for laryngeal paralysis is performed, lifespan may be similar to that of normal dogs even though affected dogs have locomotor disturbance.

Clinical and genetic investigation in Chinese patients with demyelinating Charcot-Marie-Tooth disease

Demyelinating Charcot-Marie-Tooth disease (CMT) is the most common subtype of CMT. It is caused mainly by 17p11.2 heterozygous duplication, but also by mutations in more than 20 genes which affect development and function of Schwann cells. To investigate the profile of genes mutated and clinical features in demyelinating CMT of Chinese descent, we collected a cohort of 44 demyelinating CMT patients and screened them using multiplex ligation-dependent probe amplification (MLPA) and targeted next-generation sequencing (NGS) technology. The MLPA technology revealed that 77.3% demyelinating CMT patients harbored 17p11.2 heterozygous duplication and 6.8% patients harbored heterozygous deletion of exon 6 of MPZ gene, that was further confirmed a novel c.674_675insA mutation in MPZ gene. In the patients with 17p12 heterozygous duplication, 3 sets of independent families were discordant for the CMT phenotype within the same family. The targeted NGS technology revealed that 6 candidate mutations including 1 previously reported mutation (GDAP1: c.571C>T) and 5 novel mutations (SBF2: c.415T>C, c.619G>T, c.1258A>G; GDAP1: c.589delC; PMP22: c.318delT) were found. In conclusion, combined MLPA technique with targeted NGS, the demyelinating CMT genetic diagnostic success rate was increased.

Novel SBF1 splice-site null mutation broadens the clinical spectrum of Charcot-Marie-Tooth type 4B3 disease

Four siblings of consanguineous Bedouin kindred presented at infancy with an autosomal recessive syndrome of congenital microcephaly, facial dysmorphism, strabismus, developmental delay and ataxia with positive pyramidal signs. Toward the end of their first decade, they developed areflexia, multiple cranial neuropathies and severe polyneuropathy with progressive muscle weakness, affecting proximal and distal extremities. Physical assessment exhibited kyphoscoliosis, bilateral syndactyly and distal muscle wasting with drop-foot and pes cavus. Magnetic resonance imaging (MRI) showed profound cerebellar atrophy with highly unique findings at the pontine and mesencephalic levels, previously described as "fork and bracket" signs. Genome-wide linkage analysis identified a single ~1.5 Mbp disease-associated locus on chromosome 22q13.33. Whole exome sequencing identified a single novel homozygous deleterious splice-site mutation within this locus in SET binding factor 1 (SBF1). SBF1 missense mutations were shown to underlie Charcot-Marie-Tooth (CMT) type 4B3 disease, a rare autosomal recessive subtype of CMT4. The novel SBF1 null mutation highlights distinct severe phenotypic manifestations, broadening the clinical spectrum of SBF1-related neuropathies: cerebellar and pyramidal signs evident in the first months of life with peripheral polyneuropathy emerging only toward the end of the first decade, together with unique MRI findings.

PFN2 and GAMT as common molecular determinants of axonal Charcot-Marie-Tooth disease

BACKGROUND

Charcot-Marie-Tooth type 2 (CMT2) neuropathy is characterised by a vast clinical and genetic heterogeneity complicating its diagnosis and therapeutic intervention. Identification of molecular signatures that are common to multiple CMT2 subtypes can aid in developing therapeutic strategies and measuring disease outcomes.

METHODS

A proteomics-based approach was performed on lymphoblasts from CMT2 patients genetically diagnosed with different gene mutations to identify differentially regulated proteins. The candidate proteins were validated through real-time quantitative PCR and western blotting on lymphoblast samples of patients and controls, motor neurons differentiated from patient-derived induced pluripotent stem cells (iPSCs) and sciatic nerves of CMT2 mouse models.

RESULTS

Proteomic profiling of patient lymphoblasts resulted in the identification of profilin 2 (PFN2) and guanidinoacetate methyltransferase (GAMT) as commonly downregulated proteins in different genotypes compared with healthy controls. This decrease was also observed at the transcriptional level on screening 43 CMT2 patients and 22 controls, respectively. A progressive decrease in PFN2 expression with age was observed in patients, while in healthy controls its expression increased with age. Reduced PFN2 expression was also observed in motor neurons differentiated from CMT2 patient-derived iPSCs and sciatic nerves of CMT2 mice when compared with controls. However, no change in GAMT levels was observed in motor neurons and CMT2 mouse-derived sciatic nerves.

CONCLUSIONS

We unveil PFN2 and GAMT as molecular determinants of CMT2 with possible indications of the role of PFN2 in the pathogenesis and disease progression. This is the first study describing biomarkers that can boost the development of therapeutic strategies targeting a wider spectrum of CMT2 patients.

Tracking Pain in Resting State Networks in Patients with Hereditary and Diabetic Neuropathy

Introduction

Chronic pain is associated with maladaptive plastic changes in the brain. It is usually more prominent in acquired pathologies of nerve fibers as in diabetic neuropathy despite less severe degeneration than hereditary neuropathies. Based on clinical differences concerning pain perception, we hypothesized that functional connectivity analysis would reveal distinct patterns in resting-state networks in these groups.

Methods

Ten diabetic patients with painful neuropathy (5F/5M; mean age=50.10±6.05 years), 10 patients with hereditary neuropathy (5F/5M; mean age=37.80±14.01 years), 18 age-and gender-matched healthy controls (eight for painful diabetic neuropathy and 10 for hereditary neuropathy) and seven diabetic controls without painful neuropathy were enrolled in the study. All subjects (n=45) underwent a 5-min resting-state scan in a 3T magnetic resonance scanner. The images were analyzed with seed-based functional connectivity method. The group-level maps of the default mode network and insula-cingulate network were identified for each group.

Results

Patients with hereditary neuropathy displayed increased connectivity between left insula and left anterior cingulate cortex and inversely correlated activity between left insula and left inferior parietal lobule compared to their controls. In patients with painful diabetic neuropathy, the major findings were the increased connectivity between left anterior cingulate cortex and posterior cingulate cortex/precuneus, and the increased connectivity between medial prefrontal cortex and left medial temporal region compared to their controls.

Conclusion

This study revealed that hereditary and diabetic painful neuropathy patients exhibit different patterns of functional connectivity. The clinical differences in these groups regarding the presence of neuropathic pain may relate to this difference in cortical organization.

Pathological classification of equine recurrent laryngeal neuropathy

Recurrent Laryngeal Neuropathy (RLN) is a highly prevalent and predominantly left-sided, degenerative disorder of the recurrent laryngeal nerves (RLn) of tall horses, that causes inspiratory stridor at exercise because of intrinsic laryngeal muscle paresis. The associated laryngeal dysfunction and exercise intolerance in athletic horses commonly leads to surgical intervention, retirement or euthanasia with associated financial and welfare implications. Despite speculation, there is a lack of consensus and conflicting evidence supporting the primary classification of RLN, as either a distal ("dying back") axonopathy or as a primary myelinopathy and as either a (bilateral) mononeuropathy or a polyneuropathy; this uncertainty hinders etiological and pathophysiological research. In this review, we discuss the neuropathological changes and electrophysiological deficits reported in the RLn of affected horses, and the evidence for correct classification of the disorder. In so doing, we summarize and reveal the limitations of much historical research on RLN and propose future directions that might best help identify the etiology and pathophysiology of this enigmatic disorder.

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.

Gait and footwear in children and adolescents with Charcot-Marie-Tooth disease: A cross-sectional, case-controlled study

OBJECTIVE

Children with Charcot-Marie-Tooth disease (CMT) report problems with gait and footwear. We evaluated differences in spatio-temporal gait variables and gait variability between children with CMT and typically developing (TD) children, and investigated the effect of footwear upon gait.

METHOD

A cross-sectional study of 30 children with CMT and 30 age- and gender-matched TD children aged 4-18 years. Gait was assessed at self-selected speed on an electronic walkway while barefoot and in two types of the child's own footwear; optimal (e.g., athletic-type runners) and suboptimal (e.g., flip-flops).

RESULTS

Children with CMT walked more slowly (mean (SD) -13.81 (3.61) cm/s), with shorter steps (-6.28 (1.37) cm), wider base of support (+2.47 (0.66) cm; all p < 0.001) and greater base of support variability (0.48 (0.15) cm, p = 0.002) compared to TD children. Gait was faster in optimal footwear than suboptimal (-7.55 (1.31) cm/s) and barefoot (-7.42 (1.07) cm/sec; both p < 0.001) in the combined group of children. Gait in suboptimal footwear was more variable compared to barefoot and optimal footwear. Greater base of support variability and reduced balance was moderately correlated for both groups (CMT and TD).

CONCLUSION

Gait is slower with shorter, wider steps and greater base of support variability in children with CMT. Poor balance is associated with greater base of support gait variability. Suboptimal footwear negatively affects gait in all children (CMT and TD), which has clinical implications for children and adolescents with CMT who have weaker feet and ankles, and poor balance.

Electromyographic and biomechanical analysis of step negotiation in Charcot Marie Tooth subjects whose level walk is not impaired

BACKGROUND

Charcot-Marie-Tooth (CMT) is a slowly progressive disease characterized by muscular weakness and wasting with a length-dependent pattern. Mildly affected CMT subjects showed slight alteration of walking compared to healthy subjects (HS).

RESEARCH QUESTION

To investigate the biomechanics of step negotiation, a task that requires greater muscle strength and balance control compared to level walking, in CMT subjects without primary locomotor deficits (foot drop and push off deficit) during walking.

METHODS

We collected data (kinematic, kinetic, and surface electromyographic) during walking on level ground and step negotiation, from 98 CMT subjects with mild-to-moderate impairment. Twenty-one CMT subjects (CMT-NLW, normal-like-walkers) were selected for analysis, as they showed values of normalized ROM during swing and produced work at push-off at ankle joint comparable to those of 31 HS. Step negotiation tasks consisted in climbing and descending a two-step stair. Only the first step provided the ground reaction force data. To assess muscle activity, each EMG profile was integrated over 100% of task duration and the activation percentage was computed in four phases that constitute the step negotiation tasks.

RESULTS

In both tasks, CMT-NLW showed distal muscle hypoactivation. In addition, during step-ascending CMT-NLW subjects had relevant lower activities of vastus medialis and rectus femoris than HS in weight-acceptance, and, on the opposite, a greater activation as compared to HS in forward-continuance. During step-descending, CMT-NLW showed a reduced activity of tibialis anterior during controlled-lowering phase.

SIGNIFICANCE

Step negotiation revealed adaptive motor strategies related to muscle weakness due to disease in CMT subjects without any clinically apparent locomotor deficit during level walking. In addition, this study provided results useful for tailored rehabilitation of CMT patients.

A Novel Missense Mutation in Peripheral Myelin Protein-22 Causes Charcot-Marie-Tooth Disease

Background:

Charcot-Marie-Tooth disease (CMT) is the most common inherited peripheral neuropathy. A great number of causative genes have been described in CMT, and among them, the heterozygous duplication of peripheral myelin protein-22 (PMP22) is the major cause. Although the missense mutation in PMP22 is rarely reported, it has been demonstrated to be associated with CMT. This study described a novel missense mutation of PMP22 in a Chinese family with CMT phenotype.

Methods:

Targeted next-generation sequencing (NGS) was used to screen the causative genes in a family featured with an autosomal dominant demyelinating form of CMT. The potential variants identified by targeted NGS were verified by Sanger sequencing and classified according to the American College of Medical Genetics and Genomics standards and guidelines. Further cell transfection studies were performed to characterize the function of the novel variant.

Results:

Using targeted NGS, a novel heterozygous missense variant in PMP22 (c.320G>A, p.G107D) was identified. In vitro cell functional studies revealed that mutant PMP22 protein carrying p.G107D mutation lost the ability to reach the plasma membrane, was mainly retained in the endoplasmic reticulum, and induced cell apoptosis.

Conclusions:

This study supported the notion that missense mutations in PMP22 give rise to a CMT phenotype, possibly through a toxic gain-of-function mechanism.

Motor unit number index correlates with disability in Charcot-Marie-Tooth disease

OBJECTIVE

The aim of this study was to assess the usefulness of motor unit number index (MUNIX) technique in Charcot-Marie-Tooth disease and test the correlation between MUNIX and clinical impairment.

METHODS

MUNIX technique was performed in the abductor pollicis brevis (APB), the abductor digiti minimi (ADM) and the tibialis anterior (TA) muscles in the nondominant side. A MUNIX sum score was calculated by adding the MUNIX of these 3 muscles. Muscle strength was measured using the MRC (medical research council) scale. Disability was evaluated using several functional scales, including CMT neuropathy score version 2 (CMTNSv2) and overall neuropathy limitation scale (ONLS).

RESULTS

A total of 56 CMT patients were enrolled. The MUNIX scores of the ADM, APB and TA muscles correlated with the MRC score of the corresponding muscle (p < 0.01). The MUNIX sum score correlated with the clinical scales CMTNSv2 (r  =  -0.65, p < 0.01) and ONLS (r  =  -0.57, p < 0.01).

CONCLUSION

MUNIX correlates with muscle strength and clinical measurements of disability in patients with CMT disease.

SIGNIFICANCE

The MUNIX technique evaluates motor axonal loss and correlates with disability. The MUNIX sum score may be a useful outcome measure of disease progression in CMT.

Antineoplastic agents exacerbating Charcot Marie Tooth disease: red flags to avoid permanent disability

BACKGROUND

Charcot Marie Tooth (CMT) disease is the most common form of hereditary neuropathy. Due to the high prevalence of mild and undiagnosed forms, patients with CMT disease may be exposed to severe neurotoxicity following the administration of neurotoxic chemotherapies. The aim of this report is to alert oncologists to the potential to precipitate severe irreversible peripheral neuropathies when administering neurotoxic compounds to undiagnosed CMT patients.

MATERIAL AND METHODS

A retrospective research in the OncoNeuroTox database was performed (2010-2016), searching for patients with the diagnosis of chemotherapy-induced peripheral neuropathy (CIPN) and CMT disease. A comprehensive literature review for previously published cases was performed using the Pubmed and Cochrane databases (1972-2017).

RESULTS

Among 428 patients with CIPN, we identified eight patients with concomitant CMT disease. Seven patients out of the eight had no previous diagnosis of CMT disease, although accurate familial history disclosed mild signs of peripheral neuropathy in five cases. Patients themselves had minor stigmata of long-standing peripheral damage. Patients received chemotherapy regimens based on vinca alkaloids, taxanes or a combination of vinca alkaloids and platinum compounds. In two cases, cumulative doses were below or equal to the expected neurotoxic threshold. Following chemotherapy administration, patients developed severe length-dependent sensory-motor deficits. Despite early drug discontinuation, most patients remained severely disabled.

CONCLUSION

A brief checklist to disclose long-standing signs of peripheral neuropathy could be helpful to detect patients with undiagnosed hereditary neuropathies who could be at risk of developing severe irreversible neurotoxicity following the administration of neurotoxic agents.

Substrate interaction defects in histidyl-tRNA synthetase linked to dominant axonal peripheral neuropathy

Histidyl-tRNA synthetase (HARS) ligates histidine to cognate tRNA molecules, which is required for protein translation. Mutations in HARS cause the dominant axonal peripheral neuropathy Charcot-Marie-Tooth disease type 2W (CMT2W); however, the precise molecular mechanism remains undefined. Here, we investigated three HARS missense mutations associated with CMT2W (p.Tyr330Cys, p.Ser356Asn, and p.Val155Gly). The three mutations localize to the HARS catalytic domain and failed to complement deletion of the yeast ortholog (HTS1). Enzyme kinetics, differential scanning fluorimetry (DSF), and analytical ultracentrifugation (AUC) were employed to assess the effect of these substitutions on primary aminoacylation function and overall dimeric structure. Notably, the p.Tyr330Cys, p.Ser356Asn, and p.Val155Gly HARS substitutions all led to reduced aminoacylation, providing a direct connection between CMT2W-linked HARS mutations and loss of canonical ARS function. While DSF assays revealed that only one of the variants (p.Val155Gly) was less thermally stable relative to wild-type, all three HARS mutants formed stable dimers, as measured by AUC. Our work represents the first biochemical analysis of CMT-associated HARS mutations and underscores how loss of the primary aminoacylation function can contribute to disease pathology.

Phenotypical features of two patients diagnosed with PHARC syndrome and carriers of a new homozygous mutation in the ABHD12 gene

PHARC (Polyneuropathy, Hearing loss, Ataxia, Retinitis pigmentosa and Cataracts) (MIM# 612674) is an autosomal recessive neurodegenerative disease caused by mutations in the ABHD12 gene. We evaluated two Spanish siblings affected with pes cavus, sensorimotor neuropathy, hearing loss, retinitis pigmentosa and juvenile cataracts in whom the genetic test of ABHD12 revealed a novel homozygous frameshift mutation, c.211_223del (p.Arg71Tyrfs*26). The earliest clinical manifestation in these patients was a demyelinating neuropathy manifested with a Charcot-Marie-Tooth phenotype over three decades. Progressive hearing loss, cataracts and retinitis pigmentosa appeared after the age of 30. We herein describe the complete clinical picture of these two patients, and focus particularly on neuropathy characteristics. This study supports the fact that although PHARC is rare, its phenotype is very characteristic and we should include its study in patients affected with demyelinating polyneuropathy, hearing loss and retinopathy.

Improving molecular diagnosis of Chinese patients with Charcot-Marie-Tooth by targeted next-generation sequencing and functional analysis

Charcot-Marie-Tooth (CMT) disease is the most common hereditary peripheral neuropathy. More than 50 causative genes have been identified. The lack of genotype-phenotype correlations in many CMT patients make it difficult to decide which genes are affected. Recently, targeted next-generation sequencing (NGS) has been introduced as an alternative approach for diagnosis of genetic disorders. Here, we applied targeted NGS in combination with PMP22 duplication/deletion analysis to screen causative genes in 22 Chinese CMT families. The novel variants detected by targeted NGS were then further studied in cultured cells. Of the 22 unrelated patients, 8 had PMP22 duplication. The targeted NGS revealed 10 possible pathogenic variants in 11 patients, including 7 previously reported variants and 3 novel heterozygous variants (GJB1: p.Y157H; MFN2: p.G127S; YARS: p.V293M). Further classification of the novel variants according to American College of Medical Genetics and Genomics (ACMG) standards and guidelines and functional analysis in cultured cells indicated that p.Y157H in GJB1 was pathogenic, p.G127S in MFN2 was likely pathogenic, while p.V293M in YARS was likely benign. Our results suggest the potential for targeted NGS to make a more rapid and precise diagnosis in CMT patients. Moreover, the functional analysis is required when the novel variants are indistinct.

Balance and falls in people with Charcot-Marie-Tooth disease: A cohort survey

Aim:

To explore the relationship between balance deficit, falls, and activities of daily living in a cohort with Charcot-Marie-Tooth disease.

Method:

A cohort survey of individuals with Charcot-Marie-Tooth disease attending a neurogenetic clinic was carried out. Surveys were sent to individuals on a database of a state-wide neurogenetic service located in Perth, Australia.

Results:

Out of 71 surveys, 40 were returned (56%). The cohort were predominantly male (68%), the average age was 55.5 years (range 18–84) and average age at symptom onset was 23 years (range 5–65). Excluding skeletal foot changes, balance deficits (87.5%) and loss of balance confidence (90%) were the most frequently rated symptoms and those most severely affecting physical functioning (71% and 64% respectively). Ankle splinting was frequently reported in this population (65%). The majority of participants (69%) had fallen at least once in the past year and 40% of fallers reported having never seen a physiotherapist.

Conclusions:

Despite balance deficits and loss of balance confidence being frequently reported to impact daily activities, and falls and near-falls being common in this cohort with Charcot-Marie-Tooth disease, more than a third had not seen a physiotherapist. Future management to reduce the disease burden should investigate the effects of a timely multidisciplinary approach to manage balance dysfunction, and strategies to reduce falls in this population.

X-linked Charcot-Marie-Tooth disease with GJB1 mutation presenting as acute disseminated encephalomyelitis-like illness: A case report

RATIONALE

Charcot-Marie-Tooth disease (CMT) is typically an autosomal dominant, inherited neuropathy, although there is a rare male X-linked CMT. Such patients show central nervous system (CNS) involvement in addition to peripheral neuropathy. Recently, we encountered a patient who presented with acute disseminated encephalomyelitis (ADEM)-like symptoms, but was later diagnosed as having X-linked CMT (CMTX) due to a mutation.

PATIENT CONCERNS

A previously healthy 11-year-old boy was admitted for a sudden transient weakness of his left side extremities.

DIAGNOSES

The patient was diagnosed with left side hemiparesis. Brain magnetic resonance imaging (MRI) showed ADEM-like demyelinating lesions on both centrum semiovale. A diagnosis of probable ADEM was made, and the patient soon recovered. After 4 months, a second MRI showed complete resolution of the brain lesions. However, the symptoms recurred 2 years later. A third MRI revealed white matter abnormalities, and a physical examination demonstrated pes cavus deformities and peripheral muscle wasting of both lower extremities.

INTERVENTIONS

On the basis of the brain MRI lesions and physical findings, we suspected CMTX. Genotyping confirmed a mutation in the GJB1 gene.

OUTCOMES

When the symptoms recurred 2 years later, dysarthria and demyelinating MRI lesions were present. We could not identify any triggering factors.

LESSONS

Differential diagnosis of recurrent ADEM-like lesions in the cerebral white matter and peripheral neuropathy should include the possibility of CMTX disease.

Severity of Demyelinating and Axonal Neuropathy Mouse Models Is Modified by Genes Affecting Structure and Function of Peripheral Nodes

Charcot-Marie-Tooth (CMT) disease is a clinically and genetically heterogeneous group of inherited polyneuropathies. Mutations in 80 genetic loci can cause forms of CMT, resulting in demyelination and axonal dysfunction. The clinical presentation, including sensory deficits, distal muscle weakness, and atrophy, can vary greatly in severity and progression. Here, we used mouse models of CMT to demonstrate genetic interactions that result in a more severe neuropathy phenotype. The cell adhesion molecule Nrcam and the Na⁺ channel Scn8a (NaV1.6) are important components of nodes. Homozygous Nrcam and heterozygous Scn8a mutations synergized with both an Sh3tc2 mutation, modeling recessive demyelinating Charcot-Marie-Tooth type 4C, and mutations in Gars, modeling dominant axonal Charcot-Marie-Tooth type 2D. We conclude that genetic variants perturbing the structure and function of nodes interact with mutations affecting the cable properties of axons by thinning myelin or reducing axon diameter. Therefore, genes integral to peripheral nodes are candidate modifiers of peripheral neuropathy.

Lipid Involvement in Neurodegenerative Diseases of the Motor System: Insights from Lysosomal Storage Diseases

Lysosomal storage diseases (LSDs) are a heterogeneous group of rare inherited metabolic diseases that are frequently triggered by the accumulation of lipids inside organelles of the endosomal-autophagic-lysosomal system (EALS). There is now a growing realization that disrupted lysosomal homeostasis (i.e., lysosomal cacostasis) also contributes to more common neurodegenerative disorders such as Parkinson disease (PD). Lipid deposition within the EALS may also participate in the pathogenesis of some additional neurodegenerative diseases of the motor system. Here, I will highlight the lipid abnormalities and clinical manifestations that are common to LSDs and several diseases of the motor system, including amyotrophic lateral sclerosis (ALS), atypical forms of spinal muscular atrophy, Charcot-Marie-Tooth disease (CMT), hereditary spastic paraplegia (HSP), multiple system atrophy (MSA), PD and spinocerebellar ataxia (SCA). Elucidating the underlying basis of intracellular lipid mislocalization as well as its consequences in each of these disorders will likely provide innovative targets for therapeutic research.

Evaluation of activities of daily living in patients with slowly progressive neuromuscular diseases

Slowly progressive neuromuscular diseases include but are not limited to: facioscapulohumeral muscular dystrophy (FSHD) and limb-girdle muscular dystrophy (LGMD), hereditary motor and sensory neuropathy (HMSN) and spinal muscular atrophy type III (SMA3). The purpose of this study is to present an evaluation of basic and complex activities of daily living in patients suffering from these diseases. The study was conducted on a group of 58 Polish patients: 25 patients with HMSN, 19 with LGMD and FSHD and 14 with SMA3. The research instrument consisted of two parts: a specially designed questionnaire and Nottingham Extended ADL Index. The survey was voluntary, anonymous and self-administered. In our study the highest scores on the NEADL scale were achieved by HMSN patients, and the lowest by patients with SMA3. The research revealed statistically significant differences between all the groups in the total number of points achieved on NEADL scale. The study revealed that for most respondents the most difficult tasks were those in the area of 'mobility'. It is consistent with reports in the literature, which confirm that out of the slowly progressive neuromuscular diseases included in this research, SMA3 is a disease leading to the biggest limitations in performing the activities of everyday life.

Structure, function, and regulation of mitofusin-2 in health and disease

Mitochondria are highly dynamic organelles that constantly migrate, fuse, and divide to regulate their shape, size, number, and bioenergetic function. Mitofusins (Mfn1/2), optic atrophy 1 (OPA1), and dynamin-related protein 1 (Drp1), are key regulators of mitochondrial fusion and fission. Mutations in these molecules are associated with severe neurodegenerative and non-neurological diseases pointing to the importance of functional mitochondrial dynamics in normal cell physiology. In recent years, significant progress has been made in our understanding of mitochondrial dynamics, which has raised interest in defining the physiological roles of key regulators of fusion and fission and led to the identification of additional functions of Mfn2 in mitochondrial metabolism, cell signalling, and apoptosis. In this review, we summarize the current knowledge of the structural and functional properties of Mfn2 as well as its regulation in different tissues, and also discuss the consequences of aberrant Mfn2 expression.

A novel mutation in FGD4 causes Charcot-Marie-Tooth disease type 4H with cranial nerve involvement

Charcot-Marie-Tooth disease type 4H (CMT4H) is a rare variant of autosomal recessive hereditary neuropathy. It is caused by FGD4 mutations and characterized by early infantile onset, slowly progressive distal muscle weakness, scoliosis, and myelin outfoldings visible in nerve biopsy samples. Here, we report a 65-year-old male born to consanguineous parents, who carries a novel homozygous FGD4 c.724C>T nonsense mutation. He developed lower limb weakness in his teens, which progressed slowly and was accompanied by diplopia, bilateral hearing loss, and erectile dysfunction from his twenties. At the age of 65, he was wheelchair-bound and had mild scoliosis, bilateral ophthalmoplegia, facial muscle weakness, inner ear hearing loss, distal-dominant weakness, and sensory disturbance, but no cognitive deterioration. Magnetic resonance imaging revealed enlarged bilateral trigeminal and facial nerves. Accordingly, we believe that this mutation causes slowly progressive sensorimotor neuropathy with apparent cranial nerve involvement, thereby further expanding the clinical spectrum of CMT4H.

Responsiveness of gait analysis parameters in a cohort of 71 CMT subjects

Detection of worsening in the slowly progressive Charcot-Marie-Tooth disease (CMT) is difficult. As previous clinical scales showed low responsiveness, novel outcome measures are under study, including innovative approaches such as quantitative muscle MRI and instrumented movement analysis. Since gait analysis proved able to reliably quantify CMT locomotor deficits, we aimed to explore whether it can be a sensitive-to-change outcome measure in CMT studies. Clinical and biomechanical evaluations were performed in 71 CMT subjects at baseline and after a mean (±sd) of 28.9 ± 9.5 months. Locomotor tasks included natural walking, ascending and descending steps. Instrumented analysis of such tasks provided indexes related to muscle strength (kinetic parameters) and joint movement (kinematic parameters). Parameter responsiveness was expressed as Standardized Response Mean (SRM). Considering the whole CMT group, several parameters showed moderate responsiveness; subgrouping subjects according to disease severity allowed reaching high responsiveness (SRM >0.80). CMT Examination Score showed moderate responsiveness (SRM 0.53) in the minimally affected group; kinematic parameters were more responsive in this group, whereas kinetic parameters in the most severely affected one. Biomechanical parameters can represent suitable outcome measures for CMT by showing moderate-to-high responsiveness. These data suggest that appropriate selection of patient population and outcome measures is crucial for clinical trials' design.

Traduction française de l’échelle Charcot-Marie-Tooth Disease Pediatric Scale

Cet article présente le processus de traduction en français du Charcot-Marie-Tooth Disease Pediatric Scale (CMTPedS), le seul outil de mesure validé évaluant la sévérité de la maladie chez les enfants atteints de CMT. Le processus de traduction utilisé s’inspire des lignes directrices de la Food and Drug Administration (FDA). La version préliminaire francophone du CMTPedS a été testée auprès de 14 enfants atteints. Les résultats de l’application démontrent que la passation a été bien tolérée par les enfants et s’est avérée conviviale pour les cliniciens. La disponibilité de cet outil en français semble prometteuse pour le suivi des enfants atteints et la réalisation d’essais clinique.

Molecular Epidemiology of Charcot-Marie-Tooth Disease in Northern Ostrobothnia, Finland: A Population-Based Study

BACKGROUND

Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuromuscular disorder with a population prevalence of 9.7-82.3/100,000. In this study, we have estimated the prevalence of CMT and its subtypes in Finland and examined the frequency of molecular etiologies.

METHODS

A population-based survey included adult patients with peripheral neuropathy from the province of Northern Ostrobothnia, Finland. Secondary causes of peripheral polyneuropathy were excluded and patients with clinical and neurophysiological features pertinent with CMT were included. Molecular diagnostics was carried out when DNA was available.

RESULTS

We found 107 subjects with CMT yielding a prevalence 34.6/100,000 in Northern Ostrobothnia. The heterozygous point mutation p.His123Arg in ganglioside induced differentiation associated protein 1 (GDAP1) was found in 31.5% and peripheral myelin protein 22 (PMP22) duplication in 16.9% of the affected. Point mutations in myelin protein zero, mitofusin 2, and gap junction protein beta 1 accounted for 6.7% of the cases. In addition, 18 persons had hereditary neuropathy with liability to pressure palsies and 15 of them carried the PMP22 deletion.

CONCLUSIONS

The prevalence of CMT in Northern Ostrobothnia, Finland, seems to be slightly higher than those in previous studies in European populations. Founder mutation in the GDAP1 gene accounts for a large part of the genetically defined CMT2 in Finland.

Deletion of P2 promoter of GJB1 gene a cause of Charcot-Marie-Tooth disease

X-linked Charcot-Marie-Tooth disease (CMT) is the second most common cause of CMT, and is usually caused by mutations in the gap junction protein beta 1 (GJB1) gene. This gene has nerve specific P2 promoter that work synergistically with SOX10 and EGR2 genes to initiate transcription. Mutation in this region is known to cause Schwann cell dysfunction. A single large family of X linked peripheral neuropathy was identified in our practice. Next generation sequencing for targeted panel assay identified an upstream exon-splicing deletion identified extending from nucleotide c.-5413 to approximately - c.-49. This matches the sequence of 32 nucleotides at positions c.*218-*249 in the 3'UTR downstream of the GJB1 gene. The deleted fragment included the entire P2 promoter region. The deletion segregated with the disease. To our knowledge a deletion of the P2 promoter alone as a cause of CMT has not been reported previously.

Carpal tunnel syndrome in inherited neuropathies: A retrospective survey

INTRODUCTION

This study evaluates carpal tunnel syndrome (CTS) symptom severity, functional status, and outcome of CTS therapies in patients with inherited neuropathies.

METHODS

Validated questionnaires were used to compare symptom severity and functional status in patients with and without a diagnosis of CTS and a diagnosis of an inherited neuropathy.

RESULTS

309 patients with inherited neuropathies participated in this study. The CTS symptom severity score (SSS) was found to be the most useful tool in assessing CTS severity in patients with inherited neuropathy. Splint therapy and surgery were associated with significant improvement in carpal tunnel symptoms as measured through the SSS.

DISCUSSION

This study provides insight into the assessment of CTS symptom severity and patient-reported outcomes to CTS therapy in individuals with inherited neuropathies. The SSS appears useful for evaluation of CTS symptoms and patient-reported outcomes following CTS interventions in individuals with inherited neuropathies. Muscle Nerve 57: 388-394, 2018.

Plasma metabolome and skin proteins in Charcot-Marie-Tooth 1A patients

Objective

Charcot-Marie-Tooth 1A (CMT1A) disease is the most common inherited neuropathy that lacks of therapy and of molecular markers to assess disease severity. Herein, we have pursued the identification of potential biomarkers in plasma samples and skin biopsies that could define the phenotype of CMT1A patients at mild (Mi), moderate (Mo) and severe (Se) stages of disease as assessed by the CMT neuropathy score to contribute to the understanding of CMT pathophysiology and eventually inform of the severity of the disease.

Methods

We have used: (i) a high-throughput untargeted metabolomic approach of plasma samples in a cohort of 42 CMT1A patients and 15 healthy controls (CRL) using ultrahigh liquid chromatography coupled to mass spectrometry and (ii) reverse phase protein microarrays to quantitate the expression of some proteins of energy metabolism and of the antioxidant response in skin biopsies of a cohort of 70 CMT1A patients and 13 healthy controls.

Results

The metabolomic approach identified 194 metabolites with significant differences among the four groups (Mi, Mo, Se, CRL) of samples. A multivariate Linear Discriminant Analysis model using 12 metabolites afforded the correct classification of the samples. These metabolites indicate an increase in protein catabolism and the mobilization of membrane lipids involved in signaling inflammation with severity of CMT1A. A concurrent depletion of leucine, which is required for the biogenesis of the muscle, is also observed in the patients. Protein expression in skin biopsies indicates early loss of mitochondrial and antioxidant proteins in patients’ biopsies.

Conclusion

The findings indicate that CMT1A disease is associated with a metabolic state resembling inflammation and sarcopenia suggesting that it might represent a potential target to prevent the nerve and muscle wasting phenotype in these patients. The observed changes in metabolites could be useful as potential biomarkers of CMT1A disease after appropriate validation in future longitudinal studies.

A Man With Distal Asymmetric Leg Weakness

EDUCATIONAL OBJECTIVES

To discuss a case of adult-onset asymmetric distal leg weakness in a patient who presented with weakness and atrophy of the posterior compartment of the left leg.

KEY QUESTIONS

1. What is the differential diagnosis of asymmetric distal leg weakness?2. How would a clinician approach diagnostic testing for such a patient?3. What is the final diagnosis for this patient?4. How to treat this patient?

Multiple Sites Ultrasonography of Peripheral Nerves in Differentiating Charcot-Marie-Tooth Type 1A from Chronic Inflammatory Demyelinating Polyradiculoneuropathy

Introduction

Multiple sites measurement of cross-sectional areas (CSA) by ultrasound was performed to differentiate Charcot–Marie–Tooth type 1A (CMT1A) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP).

Methods

Nine patients with CMT1A, 28 patients with CIDP, and 14 healthy controls (HC) were recruited prospectively. Consecutive ultrasonography scanning was performed from wrist to axilla on median and ulnar nerves. CSAs were measured at 10 predetermined sites of each nerve.

Results

CMT1A had significantly larger CSAs at all sites of median and ulnar nerves (p < 0.01). In CMT1A, CSAs increased gradually and homogeneously from distal to proximal along the nerve, except potential entrapment sites. CIDP displayed three different morphological patterns, including mild enlargement in 15 patients, prominent segmental enlargement in 12, and slight enlargement in 1, among which different treatment responses were observed. All patients with mild nerve enlargement treated with intravenous immunoglobulin were responsive (7/7), while less than half of those with prominent segmental enlargement (3/7) were responsive (p < 0.01).

Discussion

Consecutive scan along the nerve and multiple sites measurement by ultrasound could supply more detailed morphological feature of the nerve and help to differentiate CMT1A from CIDP.

Golgi-retained Cx32 mutants interfere with gene addition therapy for CMT1X

Numerous GJB1 gene mutations cause the X-linked form of Charcot-Marie-Tooth disease (CMT1X). GJB1 encodes connexin32 (Cx32), which forms trans-myelin gap junctions in Schwann cells. Most GJB1 mutations result in loss-of-function mechanisms, supporting the concept of gene replacement therapy. However, interactions between delivered wild type and endogenously expressed mutant Cx32 may potentially occur in the setting of gene replacement therapy. In order to screen for possible interactions of several representative CMT1X mutants with wild type Cx32 that may interfere with the functional gap junction formation, we established an in vitro screening method co-expressing in HeLa cells wild type Cx32 and one of eight different Cx32 mutants including A39P, A39V, T55I, R75W, M93V, L143P, N175D and R183S. Some of the Golgi-retained mutants hindered gap junction plaque assembly by Cx32 on the cell membrane, while co-immunoprecipitation analysis revealed a partial interaction of wild type protein with Golgi-retained mutants. Dye transfer studies confirmed that Golgi-retained R75W, M93V and N175D but not endoplasmic reticulum-retained T55I had a negative effect on wild type Cx32 function. Finally, in vivo intraneural delivery of the gene encoding the wild type Cx32 in mice bearing either the T55I or R75W mutation on Cx32 knockout background showed that virally delivered protein was correctly localized in mice expressing the endoplasmic reticulum-retained T55I whereas it did not traffic normally in mice expressing the Golgi-retained R75W. Thus, certain Golgi-retained Cx32 mutants may interfere with exogenously delivered Cx32. Screening for mutant-wild type Cx32 interactions should be considered prior to planning gene addition therapy for CMT1X.

Severe vincristine-induced polyneuropathy in a teenager with anaplastic medulloblastoma and undiagnosed Charcot-Marie-Tooth disease

Severe neuropathy is a known adverse effect of vincristine in patients with Charcot-Marie-Tooth disease (CMT). We present the case of a 16-year-old girl with anaplastic medulloblastoma treated with gross total resection and high-dose craniospinal radiation with adjuvant vincristine chemotherapy who developed acute-onset severe quadriplegia and vocal cord paralysis. Vincristine and radiation therapy were discontinued. Although her neuropathy slowly improved over several weeks, she developed metastatic extraneural medulloblastoma and died 5 months after diagnosis. Subsequent genetic testing revealed previously asymptomatic and undiagnosed CMT1A. Our case highlights the importance of early recognition of acute vincristine neurotoxicity that should raise suspicion of an underlying hereditary neuropathy.

Schwann cell mitochondria as key regulators in the development and maintenance of peripheral nerve axons

Formation of myelin sheaths by Schwann cells (SCs) enables rapid and efficient transmission of action potentials in peripheral axons, and disruption of myelination results in disorders that involve decreased sensory and motor functions. Given that construction of SC myelin requires high levels of lipid and protein synthesis, mitochondria, which are pivotal in cellular metabolism, may be potential regulators of the formation and maintenance of SC myelin. Supporting this notion, abnormal mitochondria are found in SCs of neuropathic peripheral nerves in both human patients and the relevant animal models. However, evidence for the importance of SC mitochondria in myelination has been limited, until recently. Several studies have recently used genetic approaches that allow SC-specific ablation of mitochondrial metabolic activity in living animals to show the critical roles of SC mitochondria in the development and maintenance of peripheral nerve axons. Here, we review current knowledge about the involvement of SC mitochondria in the formation and dysfunction of myelinated axons in the peripheral nervous system.

[Mitochondrial trifunctional protein deficiency: an adult patient with similar progress to Charcot-Marie-Tooth disease]

A 45-year-old man presented to us due to slowly progressive muscle weakness and sensory disturbances in his lower limbs since his 40's. He reported multiple episodes of exercise-induced severe muscle fatigue and brown urine in his childhood, which disappeared by age 20. A nerve conduction study showed peripheral axonal neuropathy and then Charcot-Marie-Tooth disease (CMT) was considered as the most likely diagnosis; however, exome sequencing failed to identify a mutation in the known genes of CMTs. Since age 55, he recurrently developed severe rhabdomyolysis that required hospitalization. On suspicion of lipid metabolism disorders, we performed serum acylcarnitine analysis, and which revealed mildly elevated long-chain fatty acids. We re-examined variants obtained via exome sequencing and found a mutation in HADHB. Mitochondrial trifunctional protein (MTP) deficiency is a rare autosomal recessive disorder of mitochondrial fatty acid beta-oxidation caused by HADHA or HADHB mutation. It can be a life-threatening multiorgan disorder with early infantile onset, but it can also present in childhood or adolescence with peripheral neuropathy and recurrent rhabdomyolysis. This case of adult-diagnosed MTP deficiency was characterized by slowly progressive peripheral neuropathy masquerading CMT in addition to muscular symptoms. MTP deficiency should be considered in patients with the combination of peripheral neuropathy and recurrent rhabdomyolysis.

Molecular pathogenesis of peripheral neuropathies: insights from Drosophila models

Peripheral neuropathies are characterized by degeneration of peripheral motor, sensory and/or autonomic axons, leading to progressive distal muscle weakness, sensory deficits and/or autonomic dysfunction. Acquired peripheral neuropathies, e.g., as a side effect of chemotherapy, are distinguished from inherited peripheral neuropathies (IPNs). Drosophila models for chemotherapy-induced peripheral neuropathy and several IPNs have provided novel insight into the molecular mechanisms underlying axonal degeneration. Forward genetic screens have predictive value for discovery of human IPN genes, and the pathogenicity of novel mutations in known IPN genes can be evaluated in Drosophila. Future screens for genes and compounds that modify Drosophila IPN phenotypes promise to make valuable contributions to unraveling the molecular pathogenesis and identification of therapeutic targets for these incurable diseases.

How far do stabilometric and clinical parameters correlate in peripheral neuropathies?

Peripheral neuropathies are characterized by the impairment of motor and sensitive nervous fibers. We aimed to investigate the correlation between proprioception, force and the limits of equilibrium parameter (LOE), by assessing 38 patients diagnosed with characterized bilateral neuropathy and 11 healthy subjects. Clinical evaluation, based on a motor and pallesthesic score, enabled their classification into groups corresponding to motor, sensitive or mixed neuropathies. Balance measures on a stabilometric platform allowed differentiation between the patients and healthy subjects but not between the groups of patients. The parameter limits of equilibrium (LOE) calculated as percentage of foot length allowed not only the differentiation between patients and healthy subjects but also between patients showing motor and sensitive forms. ROC analysis gave a threshold of 15% for LOE to discriminate between motor and sensory neuropathies with a 75% of sensitivity and 72% of specificity. Consequently, we propose a simple experimental procedure to carry out an accurate assessment of balance disorders in order to identify future rehabilitation modalities recommended to these patients.

Phenotypical features of a new dominant GDAP1 pathogenic variant (p.R226del) in axonal Charcot-Marie-Tooth disease

There are few reports on axonal CMT due to dominant GDAP1 mutations. We describe two unrelated Spanish families with a dominant axonal CMT. A novel in frame GAA deletion in exon 5 of the GDAP1 gene (c.677_679del; p.R226del) was identified in both families. Disease onset varied from early childhood to adulthood. Affected family members complained of distal lower limb weakness, cramps and foot deformities with variable CMTNS score in both families. Several individuals were asymptomatic or had paraesthesia only, however neurological examination and nerve conduction studies demonstrated neuropathic signs. Transfection of HeLa cells with the p.R226del mutation led to an increased mitochondrial aggregation. We report an AD-CMT2K with large phenotypic variability due to a novel dominant GDAP1 variant. This is the second founder GDAP1 pathogenic variant reported in Spain.

Pmp22 mutant allele-specific siRNA alleviates demyelinating neuropathic phenotype in vivo

Charcot-Marie-Tooth disease (CMT) is a genetic disorder that can be caused by aberrations in >80 genes. CMT has heterogeneous modes of inheritance, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive. Over 95% of cases are dominantly inherited. In this study, we investigated whether regulation of a mutant allele by an allele-specific small interfering RNA (siRNA) can alleviate the demyelinating neuropathic phenotype of CMT. We designed 19 different allele-specific siRNAs for Trembler J (Tr-J) mice harboring a naturally occurring mutation (Leu16Pro) in Pmp22. Using a luciferase assay, we identified an siRNA that specifically and selectively reduced the expression level of the mutant allele and reversed the low viability of Schwann cells caused by mutant Pmp22 over-expression in vitro. The in vivo efficacy of the allele-specific siRNA was assessed by its intraperitoneal injection to postnatal day 6 of Tr-J mice. Administration of the allele-specific siRNA to Tr-J mice significantly enhanced motor function and muscle volume, as assessed by the rotarod test and magnetic resonance imaging analysis, respectively. Increases in motor nerve conduction velocity and compound muscle action potentials were also observed in the treated mice. In addition, myelination, as evidenced by toluidine blue staining and electron microscopy, was augmented in the sciatic nerves of the mice after allele-specific siRNA treatment. After validating suppression of the Pmp22 mutant allele at the mRNA level in the Schwann cells of Tr-J mice, we observed increased expression levels of myelinating proteins such as myelin basic protein and myelin protein zero. These data indicate that selective suppression of the Pmp22 mutant allele by non-viral delivery of siRNA alleviates the demyelinating neuropathic phenotypes of CMT in vivo, implicating allele-specific siRNA treatment as a potent therapeutic strategy for dominantly inherited peripheral neuropathies.

Niacin-mediated Tace activation ameliorates CMT neuropathies with focal hypermyelination

Charcot–Marie–Tooth (CMT) neuropathies are highly heterogeneous disorders caused by mutations in more than 70 genes, with no available treatment. Thus, it is difficult to envisage a single suitable treatment for all pathogenetic mechanisms. Axonal Neuregulin 1 (Nrg1) type III drives Schwann cell myelination and determines myelin thickness by ErbB2/B3‐PI3K–Akt signaling pathway activation. Nrg1 type III is inhibited by the α‐secretase Tace, which negatively regulates PNS myelination. We hypothesized that modulation of Nrg1 levels and/or secretase activity may constitute a unifying treatment strategy for CMT neuropathies with focal hypermyelination as it could restore normal levels of myelination. Here we show that in vivo delivery of Niaspan, a FDA‐approved drug known to enhance TACE activity, efficiently rescues myelination in the Mtmr2^−/− mouse, a model of CMT4B1 with myelin outfoldings, and in the Pmp22^+/− mouse, which reproduces HNPP (hereditary neuropathy with liability to pressure palsies) with tomacula. Importantly, we also found that Niaspan reduces hypermyelination of Vim (vimentin)^−/− mice, characterized by increased Nrg1 type III and Akt activation, thus corroborating the hypothesis that Niaspan treatment downregulates Nrg1 type III signaling.

Evaluation of muscle strength and manual dexterity in patients with Charcot-Marie-Tooth disease

STUDY DESIGN

Matched pair study.

INTRODUCTION

Differences in hand-muscle strength/dexterity between dominant (DH) and non-dominant (NDH) hand in Charcot-Marie-Tooth disease (CMT) are not well understood.

PURPOSE OF THE STUDY

To compare muscle strength/dexterity between DH and NDH and to correlate manual dexterity, strength and sensory function.

PATIENTS AND METHODS

Thirty CMT patients were studied using functional muscle testing (FMT) and strength (dynamometry), dexterity (the Nine Hole Peg Test [NHPT]), and Jebsen-Taylor Hand Function [JTT]), and sensory function (the Nottingham Sensory Assessment [NSA]).

RESULTS

Scores were worse for DH than NDH on FMT (p = 0.043) and NHPT (p = 0.014) but not on JTT (p = 0.098), handgrip strength (p = 0.710) or tripod pinch (p = 0.645). NSA did not correlate significantly with any tests (p's0.05).

CONCLUSIONS

In CMT disease, DH appears more impaired than NDH in terms of function and dexterity. Greater muscle weakness in DH may also emerge as CMT progresses.

LEVEL OF EVIDENCE

3b.

Genotypes of CYP2C8 and FGD4 and their association with peripheral neuropathy or early dose reduction in paclitaxel-treated breast cancer patients

Background:

The purpose of this study was to evaluate single-nucleotide polymorphisms (SNPs) in genes encoding key metabolising enzymes or involved in pharmacodynamics for possible associations with paclitaxel-induced peripheral neuropathy.

Methods:

The study population consists of 188 women from the multicenter, randomised, phase II ATX trial (BOOG2006-06; EudraCT number 2006-006058-83) that received paclitaxel and bevacizumab without or with capecitabine as first-line palliative therapy of HER2-negative metastatic breast cancer. Genotyping of CYP2C8*3 (c.416G>A), CYP3A4*22 (c.522-191C>T), TUBB2A (c.-101T>C), FGD4 (c.2044-236G>A) and EPHA5 (c.2895G>A) was performed by real-time PCR. Toxicity endpoints were cumulative dose (1) until first onset of grade ⩾1 peripheral neuropathy and (2) until first paclitaxel dose reduction from related toxicity (NCI-CTCAE version 3.0). SNPs were evaluated using the Kaplan–Meier method, the Gehan–Breslow–Wilcoxon test and the multivariate Cox regression analysis.

Results:

The rate of grade ⩾1 peripheral neuropathy was 67% (n=126). The rate of dose reduction was 46% (n=87). Age ⩾65 years was a risk factor for peripheral neuropathy (HR=1.87, P<0.008), but not for dose reduction. When adjusted for age, body surface area and total cumulative paclitaxel dose, CYP2C8*3 carriers had an increased risk of peripheral neuropathy (HR=1.59, P=0.045). FGD4 c.2044-236 A-allele carriers had an increased risk of paclitaxel dose reduction (HR per A-allele=1.38, P=0.036) when adjusted for total cumulative paclitaxel dose.

Conclusions:

These findings may point towards clinically useful indicators of early toxicity, but warrant further investigation.