Gene replacement therapy in a model of Charcot-Marie-Tooth 4C neuropathy

Feasibility, Validity, and Reliability of the Virtual CMT Infant Toddler Scale (vCMTInfS): A Remote Evaluation of Infants/Toddlers With CMT

BACKGROUND AND AIMS

The CMT Infant Scale (CMTInfS) enables evaluation of infants/toddlers in clinic. Our aim was to evaluate the feasibility, reliability, and validity of a virtual version of the CMTInfS (vCMTInfS).

METHODS

Children aged 55 months or less were evaluated either in clinic using CMTInfS or remotely via telemedicine using the vCMTInfS. A trained clinical evaluator remotely directed activities with assistance from the parent/caregiver. vCMTInfS scores were calculated using the CMTInfS calculator available at www.ClinicalOutcomeMeasures.org. Clinical evaluators also used the Brazelton Neonatal Behavior assessment scale to give insight into the behavior of the child during the exam.

RESULTS

Twenty children (10 males and 10 females) aged 6-55 months with confirmed or at risk for CMT were evaluated. The mean in person (IP) CMT Infant and Toddler Scale (CMTInfS) raw score (4.11, SD = 2.76) was not significantly different from the mean initial virtual (V1) CMTInfS raw score (3.78, SD = 2.59) using a two-tailed test (t = 1.000, p = 0.347). Differences between the first and second (V2) visits as well as between the IP and V2 visits were also nonsignificant.

INTERPRETATION

Our data demonstrate that children aged 55 months or less can be effectively evaluated remotely using the vCMTInfS, which will expand the number of very young children who can be evaluated with rare forms of CMT.

Charcot-Marie-Tooth disease: a review of clinical developments and its management - What's new in 2025?

INTRODUCTION

Charcot-Marie-Tooth disease (CMT) understanding and diagnostic rates are improving. Symptomatic management is still the only option, but many therapeutic approaches are under investigation, some in the clinical trial phase.

AREAS COVERED

Through a comprehensive search in PubMed, the ClinicalTrials.gov website, and the latest abstracts on the topic, the authors review the diagnostic advances and promising treatments, focusing on pharmacological and gene therapy/silencing approaches, and on clinical trial challenges. They also review current CMT management, including rehabilitation, orthotics, and associated symptoms and comorbidities.

EXPERT OPINION

The CMT field is evolving rapidly, with significant advances in genetic diagnosis and disease recognition. International networks and patient organization partnerships are vital for progress, enabling collaboration and large-scale studies. Metabolic neuropathies are relatively easier to target, and interim analysis results from the CMT-SORD trial suggest govorestat may become the first approved CMT drug. Gene therapy shows promise but currently faces safety and targeting challenges; PMP22 silencers for CMT1A are close to being tested in patients. New drugs, such as HDAC6 inhibitors, are also approaching the clinical trial phase, despite existing hurdles. Supportive care, including rehabilitation and orthotics, continues to improve quality of life. There is optimism that within the next decade, approved therapies will reduce disease burden.

RNA Interference Targeting Small Heat Shock Protein B8 Failed to Improve Distal Hereditary Motor Neuropathy in the Mouse Model

BACKGROUND

Missense mutations in the HSPB8 gene, encoding the small heat shock protein B8, cause distal hereditary motor neuropathy (dHMN) or an axonal form of Charcot-Marie-Tooth disease (CMT subtype 2L). Mice expressing mutant Hspb8 (Lys141Asn) mimic the human disease, whereas mice lacking Hspb8 show no overt phenotype. We aimed to design an RNA interference treatment strategy that rescues the mutant HSPB8 neuronal and muscle phenotype in patient-derived motor neurons and in a knock-in mouse model of CMT2L/dHMN.

METHODS

We optimized RNA interference sequences targeting both human HSPB8 and mouse HspB8 transcripts with the aim to alleviate disease symptoms. We used human induced pluripotent stem cells and the Hspb8 knock-in mouse model. We designed lenti- and adeno-associated viral vectors that contained the short-hairpin RNA constructs. We performed expression and microscopy studies, magnetic resonance imaging, behaviour analysis and electrophysiology.

RESULTS

In CMT2L patient-derived induced pluripotent stem cells differentiated towards motor neurons, reducing the HSPB8 expression with a short-hairpin RNA (shRNA), directed towards the 3' untranslated region (3'UTR), ameliorated the morphology and fragmentation of mitochondria. The AAV9-mediated treatment of the 3'UTR shRNA construct, under neuron-specific regulation, in Hspb8 knock-in mice showed inconclusive results towards functional improvement upon expression studies, magnetic resonance imaging and neuropathological findings.

CONCLUSIONS

Given the limited beneficial effect of the treatment, the RNA interference-mediated reduction of HSPB8/Hspb8 expression might not be the best therapeutic strategy to treat dHMN/CMT2L, unless a higher viral load and earlier treatment can be applied to the mouse model.

From in vivo models to in vitro bioengineered neuromuscular junctions for the study of Charcot-Marie-Tooth disease

Peripheral neuropathies are disorders affecting the peripheral nervous system. Among them, Charcot-Marie-Tooth disease is an inherited sensorimotor neuropathy for which no effective treatment exists yet. Research on Charcot-Marie-Tooth disease has been hampered by difficulties in accessing relevant cells, such as sensory and motor neurons, Schwann cells, and myocytes, which interact at the neuromuscular junction, the specialized synapses formed between nerves and skeletal muscles. This review first outlines the various in vivo models and methods used to study neuromuscular junction deficiencies in Charcot-Marie-Tooth disease. We then explore novel in vitro techniques and models, including complex hiPSC-derived cultures, which offer promising isogenic and reproducible neuromuscular junction models. The adaptability of in vitro culture methods, including cell origin, cell-type combinations, and choice of culture format, adds complexity and excitement to this rapidly evolving field. This review aims to recapitulate available tools for studying Charcot-Marie-Tooth disease to understand its pathophysiological mechanisms and test potential therapies.

Clinical Outcome Assessments and Biomarkers in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth disease (CMT) encompasses a diverse group of genetic forms of inherited peripheral neuropathy and stands as the most common hereditary neurologic disease worldwide. At present, no disease-modifying treatments exist for any form of CMT. However, promising therapeutic strategies are rapidly emerging, necessitating careful consideration of clinical outcome assessments (COAs) and clinical trial design. In this review, we discuss the challenges and successes over the past 2 decades in efforts to design and validate COAs and disease biomarkers of CMT. Natural history studies and completed clinical trials have underscored the limitations of early clinical scales for CMT, including the neuropathy impairment score, overall neuropathy limitation scale, and CMT neuropathy score. These studies prompted the development of newer, psychometrically supported scales including the CMT neuropathy score version 2, CMT pediatric scale, CMT infant scale, CMT functional outcome measure, and CMT health index. Although promising, many of these scales have yet to be formally tested in longitudinal studies. Given inherent challenges of relying solely on COAs in slowly progressive forms of CMT, there is growing recognition of the need for objective disease biomarkers that could serve as surrogate end points in clinical trials. Among these, MRI muscle fat fraction in the lower extremities has proven the most responsive biomarker to date, although its relationship to functional outcomes and its performance in treatment trials remain uncertain. Serum biomarkers including neurofilament light, transmembrane protease serine 5, specific microRNAs, neural cell adhesion molecule 1, and growth and differentiation factor 15 reliably distinguish patients with CMT from controls, but their responsiveness to effective therapies also remains unknown. Although the optimal combination of outcome measures in CMT has yet to be established, many of the most promising COAs and biomarkers are now being put to the test in ongoing clinical trials. These early studies will also help address other critical clinical trial considerations, such as patient selection and enrollment targets, which will become increasingly important in this exciting new era of bringing the first disease-modifying treatments to people living with CMT.

AAV1.tMCK.NT-3 gene therapy improves phenotype in Sh3tc2-/- mouse model of Charcot-Marie-Tooth Type 4C

Charcot-Marie-Tooth Type 4C (CMT4C) is associated with mutations in the SH3 domain and tetratricopeptide repeats 2 (SH3TC2) gene, primarily expressed in Schwann cells (SCs). Neurotrophin-3 (NT-3) is an important autocrine factor for SC survival and differentiation, and it stimulates neurite outgrowth and myelination. In this study, scAAV1.tMCK.NT-3 was delivered intramuscularly to 4-week-old Sh3tc2-/- mice, a model for CMT4C, and treatment efficacy was assessed at 6-month post-gene delivery. Efficient transgene production was verified with the detection of NT-3 in serum from the treated cohort. NT-3 gene therapy improved functional and electrophysiological outcomes including rotarod, grip strength and nerve conduction velocity. Qualitative and quantitative histopathological studies showed that hypomyelination of peripheral nerves and denervated status of neuromuscular junctions at lumbrical muscles were also improved in the NT-3-treated mice. Morphometric analysis in mid-sciatic and tibial nerves showed treatment-induced distally prominent regenerative activity in the nerve and an increase in the estimated SC density. This indicates that SC proliferation and differentiation, including the promyelination stage, are normal in the Sh3tc2-/- mice, consistent with the previous findings that Sh3tc2 is not involved in the early stages of myelination. Moreover, in size distribution histograms, the number of myelinated axons within the 3- to 6-µm diameter range increased, suggesting that treatment resulted in continuous radial growth of regenerating axons over time. In conclusion, this study demonstrates the efficacy of AAV1.NT-3 gene therapy in the Sh3tc2-/- mouse model of CMT4C, the most common recessively inherited demyelinating CMT subtype.

Novel AAV variants with improved tropism for human Schwann cells

Gene therapies and associated technologies are transforming biomedical research and enabling novel therapeutic options for patients living with debilitating and incurable genetic disorders. The vector system based on recombinant adeno-associated viral vectors (AAVs) has shown great promise in recent clinical trials for genetic diseases of multiple organs, such as the liver and the nervous system. Despite recent successes toward the development of novel bioengineered AAV variants for improved transduction of primary human tissues and cells, vectors that can efficiently transduce human Schwann cells (hSCs) have yet to be identified. Here, we report the application of the functional transduction-RNA selection method in primary hSCs for the development of AAV variants for specific and efficient transgene delivery to hSCs. The two identified capsid variants, Pep2hSC1 and Pep2hSC2, show conserved potency for delivery across various in vitro, in vivo, and ex vivo models of hSCs. These novel AAV capsids will serve as valuable research tools, forming the basis for therapeutic solutions for both SC-related disorders or peripheral nervous system injury.

Genetic Landscape of SH3TC2 variants in Russian patients with Charcot-Marie-Tooth disease

Introduction

Charcot-Marie-Tooth disease type 4C (CMT4C) OMIM#601596 stands out as one of the most prevalent forms of recessive motor sensory neuropathy worldwide. This disorder results from biallelic pathogenic variants in the SH3TC2 gene.

Methods

Within a cohort comprising 700 unrelated Russian patients diagnosed with Charcot-Marie-Tooth disease, we conducted a gene panel analysis encompassing 21 genes associated with hereditary neuropathies. Among the cohort, 394 individuals exhibited demyelinating motor and sensory neuropathy.

Results and discussion

Notably, 10 cases of CMT4C were identified within this cohort. The prevalence of CMT4C among Russian demyelinating CMT patients lacking the PMP22 duplication is estimated at 2.5%, significantly differing from observations in European populations. In total, 4 novel and 9 previously reported variants in the SH3TC2 gene were identified. No accumulation of a major variant was detected. Three previously reported variants, c.2860C>T p. (Arg954*), p. (Arg658Cys) and c.279G>A p. (Lys93Lys), recurrently detected in unrelated families. Nucleotide alteration p. (Arg954*) is present in most of our patients (30%).

Lumbar Intrathecal Injection in Adult and Neonatal Mice

This article describes a step-by-step process of lumbar intrathecal injection of Evans blue dye and AAV9-EGFP in adult (2-month-old) and neonatal (postnatal day 10) mice. Intrathecal injection is a clinically translatable technique that has already been extensively applied in humans. In mice, intrathecal injection is considered a challenging procedure that requires a trained and experienced researcher. For both adult and neonatal mice, lumbar intrathecal injection is directed into the L5-L6 intervertebral space. Intrathecally injected material enters the cerebrospinal fluid (CSF) within the intrathecal space from where it can directly access the central nervous system (CNS) parenchyma. Simultaneously, intrathecally injected material exits the CSF with pressure gradient and enters the endoneurial fluid and ultimately the peripheral nerves. While in the CSF, the injectable material also enters the bloodstream and systemic circulation through the arachnoid villi. A successful lumbar intrathecal injection results in adequate biodistribution of the injectable material in the CNS, PNS, and peripheral organs. When correctly applied, this technique is considered as minimally invasive and non-disruptive and can be used for the lumbar delivery of any solute. © 2024 Wiley Periodicals LLC. Basic Protocol 1: C57BL/6 adult and P10 mice lumbar intrathecal injection Basic Protocol 2: Tissue collection and preparation for evaluating Evans blue dye diffusion Basic Protocol 3: Tissue collection and preparation for immunohistochemistry staining Basic Protocol 4: Tissue collection and vector genome copy number analysis.

Charcot-Marie-tooth disease type 2A: An update on pathogenesis and therapeutic perspectives

Mutations in the gene encoding MFN2 have been identified as associated with Charcot-Marie-Tooth disease type 2A (CMT2A), a neurological disorder characterized by a broad clinical phenotype involving the entire nervous system. MFN2, a dynamin-like GTPase protein located on the outer mitochondrial membrane, is well-known for its involvement in mitochondrial fusion. Numerous studies have demonstrated its participation in a network crucial for various other mitochondrial functions, including mitophagy, axonal transport, and its controversial role in endoplasmic reticulum (ER)-mitochondria contacts. Considerable progress has been made in the last three decades in elucidating the disease pathogenesis, aided by the generation of animal and cellular models that have been instrumental in studying disease physiology. A review of the literature reveals that, up to now, no definitive pharmacological treatment for any CMT2A variant has been established; nonetheless, recent years have witnessed substantial progress. Many treatment approaches, especially concerning molecular therapy, such as histone deacetylase inhibitors, peptide therapy to increase mitochondrial fusion, the new therapeutic strategies based on MF1/MF2 balance, and SARM1 inhibitors, are currently in preclinical testing. The literature on gene silencing and gene replacement therapies is still limited, except for a recent study by Rizzo et al.(Rizzo et al., 2023), which recently first achieved encouraging results in in vitro and in vivo models of the disease. The near-future goal for these promising therapies is to progress to the stage of clinical translation.

Late Onset of Severe Demyelinating Peripheral Neuropathy in a 62-Year-Old African American Woman

ABSTRACT

Hereditary neuropathies are typically associated with an early onset of symptoms, but same types of neuropathies may also manifest late, after the age 50 years. A 62-year-old African American woman presented with a 6-year history of gait unsteadiness and has been using a walker since the age 57 years after an unwitnessed fall. Gradual worsening of walking difficulties was later followed by decreased dexterity. The family history was negative for neuromuscular disorders, including neuropathy. On examination, the patient had both distal and proximal weakness with distal sensory loss to all modalities and hyporeflexia. Charcot Marie Tooth Examination Score was 12. Previous electrodiagnostic testing at the age 60 years showed severe sensorimotor demyelinating polyneuropathy with bilateral severe carpal tunnel syndrome. Genetic testing showed a homozygous pathogenic mutation in SH3TC2 gene (c.2860C>T; p.Arg954*), associated with CMT4C. CMT4C is the most common recessive demyelinating sensorimotor polyneuropathy and overall comprises 0.4%-1.7% of all patients with Charcot-Marie-Tooth disease. It is more common in French Canadians and Spanish Roma and in recent natural history study; only 1 of 56 patients was African American. This report demonstrates sporadic occurrence of CMT4C in other ethnic groups as well.

Ropivacaine Promotes Axon Regeneration by Regulating Nav1.8-mediated Macrophage Signaling after Sciatic Nerve Injury in Rats

BACKGROUND

Continuous nerve block with ropivacaine is commonly performed after repair surgery for traumatic peripheral nerve injuries. After peripheral nerve injury, tetrodotoxin-resistant voltage-gated sodium channel Nav1.8 is upregulated and contributes to macrophage inflammation. This study investigated whether ropivacaine promotes peripheral nerve regeneration through Nav1.8-mediated macrophage signaling.

METHODS

A sciatic nerve transection-repair (SNT) model was established in adult Sprague-Dawley rats of both sexes. The rats received 0.2% ropivacaine or 10 μM Nav1.8-selective inhibitor A-803467 around the injured site or near the sacrum for 3 days. Nerve regeneration was evaluated using behavioral, electrophysiologic, and morphological examinations. Moreover, myelin debris removal, macrophage phenotype, Nav1.8 expression, and neuropeptide expression were assessed using immunostaining, enzyme-linked immunosorbent assay, and Western blotting.

RESULTS

Compared to the SNT-plus-vehicle group, the sensory, motor, and sensory-motor coordination functions of the two ropivacaine groups were significantly improved. Electrophysiologic (mean ± SD: recovery index of amplitude, vehicle 0.43 ± 0.17 vs. ropivacaine 0.83 ± 0.25, n = 11, P < 0.001) and histological analysis collectively indicated that ropivacaine significantly promoted axonal regrowth (percentage of neurofilament 200 [NF-200]-positive area: vehicle 19.88 ± 2.81 vs. ropivacaine 31.07 ± 2.62, n = 6, P < 0.001). The authors also found that, compared to the SNT-plus-vehicle group, the SNT-plus-ropivacaine group showed faster clearance of myelin debris, accompanied by significantly increased macrophage infiltration and transition from the M1 to M2 phenotype. Moreover, ropivacaine significantly attenuated Nav1.8 upregulation at 9 days after sciatic nerve transection (vehicle 4.12 ± 0.30-fold vs. ropivacaine 2.75 ± 0.36-fold, n = 5, P < 0.001), which coincided with the increased expression of chemokine ligand 2 and substance P. Similar changes were observed when using the selective Nav1.8 channel inhibitor A-803467.

CONCLUSIONS

Continuous nerve block with ropivacaine promotes the structural and functional recovery of injured sciatic nerves, possibly by regulating Nav1.8-mediated macrophage signaling.

EDITOR’S PERSPECTIVE

Combined RNA interference and gene replacement therapy targeting MFN2 as proof of principle for the treatment of Charcot-Marie-Tooth type 2A

Mitofusin-2 (MFN2) is an outer mitochondrial membrane protein essential for mitochondrial networking in most cells. Autosomal dominant mutations in the MFN2 gene cause Charcot-Marie-Tooth type 2A disease (CMT2A), a severe and disabling sensory-motor neuropathy that impacts the entire nervous system. Here, we propose a novel therapeutic strategy tailored to correcting the root genetic defect of CMT2A. Though mutant and wild-type MFN2 mRNA are inhibited by RNA interference (RNAi), the wild-type protein is restored by overexpressing cDNA encoding functional MFN2 modified to be resistant to RNAi. We tested this strategy in CMT2A patient-specific human induced pluripotent stem cell (iPSC)-differentiated motor neurons (MNs), demonstrating the correct silencing of endogenous MFN2 and replacement with an exogenous copy of the functional wild-type gene. This approach significantly rescues the CMT2A MN phenotype in vitro, stabilizing the altered axonal mitochondrial distribution and correcting abnormal mitophagic processes. The MFN2 molecular correction was also properly confirmed in vivo in the MitoCharc1 CMT2A transgenic mouse model after cerebrospinal fluid (CSF) delivery of the constructs into newborn mice using adeno-associated virus 9 (AAV9). Altogether, our data support the feasibility of a combined RNAi and gene therapy strategy for treating the broad spectrum of human diseases associated with MFN2 mutations.

AAV9-mediated SH3TC2 gene replacement therapy targeted to Schwann cells for the treatment of CMT4C

Type 4C Charcot-Marie-Tooth (CMT4C) demyelinating neuropathy is caused by autosomal recessive SH3TC2 gene mutations. SH3TC2 is highly expressed in myelinating Schwann cells. CMT4C is a childhood-onset progressive disease without effective treatment. Here, we generated a gene therapy for CMT4C mediated by an adeno-associated viral 9 vector (AAV9) to deliver the human SH3TC2 gene in the Sh3tc2-/- mouse model of CMT4C. We used a minimal fragment of the myelin protein zero (Mpz) promoter (miniMpz), which was cloned and validated to achieve Schwann cell-targeted expression of SH3TC2. Following the demonstration of AAV9-miniMpz.SH3TC2myc vector efficacy to re-establish SH3TC2 expression in the peripheral nervous system, we performed an early as well as a delayed treatment trial in Sh3tc2-/- mice. We demonstrate both after early as well as following late treatment improvements in multiple motor performance tests and nerve conduction velocities. Moreover, treatment led to normalization of the organization of the nodes of Ranvier, which is typically deficient in CMT4C patients and Sh3tc2-/- mice, along with reduced ratios of demyelinated fibers, increased myelin thickness and reduced g-ratios at both time points of intervention. Taken together, our results provide a proof of concept for an effective and potentially translatable gene replacement therapy for CMT4C treatment.

Intravenous Administration of an AAV9 Vector Ubiquitously Expressing C1orf194 Gene Improved CMT-Like Neuropathy in C1orf194-/- Mice

Charcot-Marie-Tooth (CMT) disease, also known as hereditary motor sensory neuropathy, is a group of rare genetically heterogenous diseases characterized by progressive muscle weakness and atrophy, along with sensory deficits. Despite extensive pre-clinical and clinical research, no FDA-approved therapy is available for any CMT type. We previously identified C1ORF194, a novel causative gene for CMT, and found that both C1orf194 knock-in (I121N) and knockout mice developed clinical phenotypes similar to those in patients with CMT. Encouraging results of adeno-associated virus (AAV)-mediated gene therapy for spinal muscular atrophy have stimulated the use of AAVs as vehicles for CMT gene therapy. Here, we present a gene therapy approach to restore C1orf194 expression in a knockout background. We used C1orf194-/- mice treated with AAV serotype 9 (AAV9) vector carrying a codon-optimized WT human C1ORF194 cDNA whose expression was driven by a ubiquitously expressed chicken β-actin promoter with a CMV enhancer. Our preclinical evaluation demonstrated the efficacy of AAV-mediated gene therapy in improving sensory and motor abilities, thus achieving largely normal gross motor performance and minimal signs of neuropathy, on the basis of neurophysiological and histopathological evaluation in C1orf194-/- mice administered AAV gene therapy. Our findings advance the techniques for delivering therapeutic interventions to individuals with CMT.

Clinical trials in Charcot-Marie-Tooth disorders: a retrospective and preclinical assessment

Objective

This study aimed to evaluate the progression of clinical and preclinical trials in Charcot-Marie-Tooth (CMT) disorders.

Background

CMT has historically been managed symptomatically and with genetic counseling. The evolution of molecular and pathologic understanding holds a therapeutic promise in gene-targeted therapies.

Methods

ClinicalTrials.gov from December 1999 to June 2022 was data extracted for CMT with preclinical animal gene therapy trials also reviewed by PubMed search.

Results

The number of active trials was 1 in 1999 and 286 in 2022. Academic settings accounted for 91% and pharmaceutical companies 9%. Of the pharmaceutical and academic trials, 38% and 28%, respectively, were controlled, randomized, and double-blinded. Thirty-two countries participated: the United States accounted for 26% (75/286). In total, 86% of the trials were classified as therapeutic: 50% procedural (21% wrist/elbow surgery; 22% shock wave and hydrodissection therapy), 23% investigational drugs, 15% devices, and 11% physical therapy. Sixty-seven therapeutic trials (49%) were designated phases 1-2 and 51% phases 3-4. The remaining 14% represent non-therapeutic trials: diagnostic testing (3%), functional outcomes (4%), natural history (4%), and standard of care (3%). One-hundred and three (36%) resulted in publications. Phase I human pharmaceutical trials are focusing on the safety of small molecule therapies (n = 8) and AAV and non-viral gene therapy (n = 3). Preclinical animal gene therapy studies include 11 different CMT forms including viral, CRISPR-Cas9, and nanoparticle delivery.

Conclusion

Current CMT trials are exploring procedural and molecular therapeutic options with substantial participation of the pharmaceutical industry worldwide. Emerging drug therapies directed at molecular pathogenesis are being advanced in human clinical trials; however, the majority remain within animal investigations.

Gene replacement therapy in two Golgi-retained CMT1X mutants before and after the onset of demyelinating neuropathy

X-linked Charcot-Marie-Tooth disease type 1 (CMT1X) is a demyelinating neuropathy resulting from loss-of-function mutations affecting the GJB1/connexin 32 (Cx32) gene. We previously showed functional and morphological improvement in Gjb1-null mice following AAV9-mediated delivery of human Cx32 driven by the myelin protein zero (Mpz) promoter in Schwann cells. However, CMT1X mutants may interfere with virally delivered wild-type (WT) Cx32. To confirm the efficacy of this vector also in the presence of CMT1X mutants, we delivered AAV9-Mpz-GJB1 by lumbar intrathecal injection in R75W/Gjb1-null and N175D/Gjb1-null transgenic lines expressing Golgi-retained mutations, before and after the onset of the neuropathy. Widespread expression of virally delivered Cx32 was demonstrated in both genotypes. Re-establishment of WT Cx32 function resulted in improved muscle strength and increased sciatic nerve motor conduction velocities in all treated groups from both mutant lines when treated before as well as after the onset of the neuropathy. Furthermore, morphological analysis showed improvement of myelination and reduction of inflammation in lumbar motor roots and peripheral nerves. In conclusion, this study provides proof of principle for a clinically translatable gene therapy approach to treat CMT1X before and after the onset of the neuropathy, even in the presence of endogenously expressed Golgi-retained Cx32 mutants.

Neuropathy due to bi-allelic SH3TC2 variants: genotype-phenotype correlation and natural history

Recessive SH3TC2 variants cause Charcot-Marie-Tooth disease type 4C (CMT4C). CMT4C is typically a sensorimotor demyelinating polyneuropathy, marked by early onset spinal deformities, but its clinical characteristics and severity are quite variable. Clear relationships between pathogenic variants and the spectrum of disease manifestations are to date lacking. Gene replacement therapy has been shown to ameliorate the phenotype in a mouse model of CMT4C, emphasizing the need for natural history studies to inform clinical trial readiness. Data, including both genetic information and clinical characteristics, were compiled from the longitudinal, prospective dataset of the Inherited Neuropathy Consortium, a member of the Rare Diseases Clinical Research Network (INC-RDCRN). The Charcot Marie Tooth Neuropathy Score (CMTNS), Examination Score (CMTES) and the Rasch-weighted CMTES (CMTES-R) were used to describe symptoms, neurological examinations and neurophysiological characteristics. Standardized response means were calculated at yearly intervals and a mixed model for repeated measures was used to estimate the change in CMTES and CMTES-R over time. Fifty-six individuals (59% female), median age 27 years (range 2-67 years) with homozygous or compound heterozygous variants in SH3TC2 were identified, including 34 unique variants, 14 of which have not previously been published. Twenty-eight participants had longitudinal data available. While there was no significant difference in the CMTES in those with protein truncating versus non-protein truncating variants, there were significant differences in the mean ulnar nerve compound muscle action potential amplitude, the mean radial sensory nerve action potential amplitude, and in the prevalence of scoliosis, suggesting the possibility of a milder phenotype in individuals with one or two non-protein-truncating variants. Overall, the mean value of the CMTES was 13, reflecting moderate clinical severity. There was a high rate of scoliosis (81%), scoliosis surgery (36%), and walking difficulty (94%) among study participants. The CMTES and CMTES-R appeared moderately responsive to change over extended follow-up, demonstrating a standardized response mean of 0.81 standard deviation units or 0.71 standard deviation units, respectively, over 3 years. Our analysis represents the largest cross-sectional and only longitudinal study to date, of the clinical phenotype of both adults and children with CMT4C. With the promise of upcoming genetic treatments, these data will further define the natural history of the disease and inform study design in preparation for clinical trials.

Characterisation of Patients with SH3TC2 Associated Neuropathy in an Indian Cohort

Background

SH3TC2 variations lead to demyelinating recessive Charcot-Marie-Tooth (CMT) disease, which is commonly associated with early-onset scoliosis and cranial neuropathy. Data from Indian ethnicity is limited.

Objective

We aim to report the characteristics of patients with SH3TC2-associated neuropathy from an Indian cohort.

Patients and Methods

Data of five unrelated subjects with SH3TC2 variations were analyzed.

Results

Clinical features included female predominance (n = 4), early-onset neuropathy (n = 2), pes cavus and hammer toes (n = 4), kyphoscoliosis (n = 1), impaired vision and hearing (n = 1), facial muscle weakness (n = 1), impaired kinaesthetic sense (n = 3), tremor (n = 2), and ataxia (n = 1). Four patients had the "CMT" phenotype, while one patient had Roussy-Levy syndrome. All had demyelinating electrophysiology with conduction velocities being "very slow" in one, "slow" in one, "mildly slow" in two, and "intermediate" in one patient. Brain stem auditory evoked potentials were universally abnormal though only one patient had symptomatic deafness. Seven variants were identified in SH3TC2 [homozygous = 3 (c.1412del, c.69del, c.3152G>A), heterozygous = 4 (c.1105C>T, c.3511C>T, c.2028G>C, c.254A>T)]. Except for c.3511C>T variant, the rest were novel. Three patients had additional variations in genes having pathobiological relevance in other CMTs or amyotrophic lateral sclerosis.

Conclusion

We provide data on a cohort of patients of Indian origin with SH3TC2 variations and highlight differences from other cohorts. Though the majority were not symptomatic for hearing impairment, evoked potentials disclosed abnormalities in all. Further studies are required to establish the functional consequences of novel variants and their interacting molecular partners identified in the present study to strengthen their association with the phenotype.

Gene therapy and other novel treatment approaches for Charcot-Marie-Tooth disease

There is still no effective drug treatment available for Charcot-Marie-Tooth disease (CMT). Current management relies on rehabilitation therapy, surgery for skeletal deformities, and symptomatic treatment. The challenge is to find disease-modifying therapies. Several approaches, including gene silencing (by means of ASO, siRNA, shRNA, miRNA, CRISPR-Cas9 editing), to counteract the PMP22 gene overexpression in the most frequent CMT1A type are under investigation. PXT3003 is the compound in the most advanced phase for CMT1A, as a second phase-III trial is ongoing. Gene therapy to substitute defective genes (particularly in recessive forms associated with loss-of-function mutations) or insert novel ones (e.g., NT3 gene) are being developed and tested in animal models and in still exceptional cases have reached the clinical trial phase in humans. Novel treatment approaches are also aimed at developing compounds acting on pathways important for different CMT types. Modulation of the neuregulin pathway determining myelin thickness is promising for both hypo-demyelinating and hypermyelinating neuropathies; intervention on Unfolded Protein Response seems effective for rescuing misfolded myelin proteins such as MPZ in CMT1B. HDAC6 inhibitors improved axonal transport and ameliorated phenotypes in different CMT models. Other potential therapeutic strategies include targeting macrophages, lipid metabolism, and Nav1.8 sodium channel in demyelinating CMT and the P2×7 receptor, which regulates calcium influx into Schwann cells, in CMT1A. Further approaches are aimed at correcting metabolic abnormalities, including the accumulation of sorbitol caused by biallelic mutations in the sorbitol dehydrogenase (SORD) gene and of neurotoxic glycosphingolipids in HSN1.

Validation of the parent-proxy pediatric Charcot-Marie-Tooth disease quality of life outcome measure

Charcot-Marie-Tooth disease (CMT) reduces health-related quality of life (QOL) in children. We have previously developed and validated the English and Italian versions of the pediatric CMT-specific QOL outcome measure (pCMT-QOL) for children aged 8 to 18. There is currently no parent-proxy CMT QOL outcome measure for use in clinical trials, which could provide complementary information in these children and adolescents. This study describes the validation studies conducted to develop the parent-proxy version of the pCMT-QOL outcome measure for children aged 8 to 18 years old. Development and validation of the parent-proxy version of the pCMT-QOL outcome measure for children aged 8 to 18 years old was iterative, involving identifying relevant domains, item pool generation, prospective pilot testing and clinical assessments, structured focus-group interviews, and psychometric testing, conducted on parents of children with CMT seen at participating sites from the USA, United Kingdom, and Australia. We utilized previously described methods to develop a working parent-proxy version of the pCMT-QOL measure. From 2010 to 2016, the parent-proxy pCMT-QOL working version was administered to 358 parents of children with CMT aged 8 to 18, seen at the participating study sites of the Inherited Neuropathies Consortium. The resulting data underwent rigorous psychometric analysis, including factor analysis, test-retest reliability, internal consistency, convergent validity, IRT analysis, and longitudinal analysis, to develop the final parent-proxy version of the pCMT-QOL outcome measure for children aged 8 to 18 years old. The parent-proxy version of the pCMT-QOL outcome measure is a reliable, valid, and sensitive proxy measure of health-related QOL for children aged 8 to 18 with CMT.

Trials for Slowly Progressive Neurogenetic Diseases Need Surrogate Endpoints

Heritable neurological disorders provide insights into disease mechanisms that permit development of novel therapeutic approaches including antisense oligonucleotides, RNA interference, and gene replacement. Many neurogenetic diseases are rare and slowly progressive making it challenging to measure disease progression within short time frames. We share our experience developing clinical outcome assessments and disease biomarkers in the inherited peripheral neuropathies. We posit that carefully developed biomarkers from imaging, plasma, or skin can predict meaningful progression in functional and patient reported outcome assessments such that clinical trials of less than 2 years will be feasible for these rare and ultra-rare disorders. ANN NEUROL 2023;93:906-910.

Treatment of Charcot-Marie-Tooth neuropathies

Charcot-Marie-Tooth (CMT) is a heterogeneous group of inherited neuropathies that affect the peripheral nerves and slowly cause progressive disability. Currently, there is no effective therapy. Patients' management is based on rehabilitation and occupational therapy, fatigue, and pain treatment with regular follow-up according to the severity of the disease. In the last three decades, much progress has been made to identify mutations involved in the different types of CMT, decipher the pathophysiology of the disease, and identify key genes and pathways that could be targeted to propose new therapeutic strategies. Genetic therapy is one of the fields of interest to silence genes such as PMP22 in CMT1A or to express GJB1 in CMT1X. Among the most promising molecules, inhibitors of the NRG-1 axis and modulators of UPR or the HDACs enzyme family could be used in different types of CMT.

Pan-Cancer Analysis Reveals SH3TC2 as an Oncogene for Colorectal Cancer and Promotes Tumorigenesis via the MAPK Pathway

SH3 domain and tetrapeptide repeat 2 (SH3TC2) is a protein-encoding gene and has previously been described as a critical signaling hub for neurological disorders. Although increasing evidence supports a vital role of SH3TC2 in the tumorigenesis of various kinds of cancer, no systematic analysis of SH3TC2 is available. The function and mechanism of SH3TC2 in other cancers remain unknown. Thus, this study aimed to analyze SH3TC2 in various kinds of cancer to find its tumorigenic role in one or more specific cancers. In the current study, we analyzed the expression level and prognostic value of SH3TC2 in different tumors in the TCGA-GTEx pan-cancer dataset. Subsequently, the prognostic role and mechanism of SH3TC2 in colorectal cancer (CRC) were further explored via clinical samples and in vitro and in vivo experiments. We observed differential expression of SH3TC2 in colon adenocarcinoma (COAD), acute myeloid leukemia (LAML), READ (rectum adenocarcinoma), SKCM (skin cutaneous melanoma), and TGCT (testicular germ cell tumors). Subsequently, SH3TC2 showed a significant effect on the clinical stage and prognostic value in CRC, LAML, and SKCM. Moreover, we found in the TCGA database and seven GEO datasets that SH3TC2 was significantly highly expressed in tumor tissue. Through enrichment analysis of SH3TC2 and its co-expressed genes, we found that SH3TC2 may play a role in the MAPK signaling pathway. Correlation analysis indicated that SH3TC2 was significantly associated with multiple key factors in the MAPK signaling pathway. Additionally, higher expression of SH3TC2 was found in tumor tissue in our cohort including 40 CRC patients. Overexpression of SH3TC2 may imply poor prognosis. Knockdown of SH3TC2 significantly inhibited tumor invasion, migration, and proliferation. More importantly, knockdown of SH3TC2 inhibited tumor growth in a CRC mouse model. The study preliminarily conducted a pan-cancer study of SH3TC2 and further explored the mechanism of SH3TC2 in CRC. Our research revealed that higher expression of SH3TC2 may promote CRC progression and invasion via the MAPK signaling pathway.

A translatable RNAi-driven gene therapy silences PMP22/Pmp22 genes and improves neuropathy in CMT1A mice

Charcot-Marie-Tooth disease type 1A (CMT1A), the most common inherited demyelinating peripheral neuropathy, is caused by PMP22 gene duplication. Overexpression of WT PMP22 in Schwann cells destabilizes the myelin sheath, leading to demyelination and ultimately to secondary axonal loss and disability. No treatments currently exist that modify the disease course. The most direct route to CMT1A therapy will involve reducing PMP22 to normal levels. To accomplish this, we developed a gene therapy strategy to reduce PMP22 using artificial miRNAs targeting human PMP22 and mouse Pmp22 mRNAs. Our lead therapeutic miRNA, miR871, was packaged into an adeno-associated virus 9 (AAV9) vector and delivered by lumbar intrathecal injection into C61-het mice, a model of CMT1A. AAV9-miR871 efficiently transduced Schwann cells in C61-het peripheral nerves and reduced human and mouse PMP22 mRNA and protein levels. Treatment at early and late stages of the disease significantly improved multiple functional outcome measures and nerve conduction velocities. Furthermore, myelin pathology in lumbar roots and femoral motor nerves was ameliorated. The treated mice also showed reductions in circulating biomarkers of CMT1A. Taken together, our data demonstrate that AAV9-miR871–driven silencing of PMP22 rescues a CMT1A model and provides proof of principle for treating CMT1A using a translatable gene therapy approach.

Clinical and genetic features of a cohort of patients with MFN2-related neuropathy

Charcot–Marie–Tooth disease type 2A (CMT2A) is a rare inherited axonal neuropathy caused by mutations in MFN2 gene, which encodes Mitofusin 2, a transmembrane protein of the outer mitochondrial membrane. We performed a cross-sectional analysis on thirteen patients carrying mutations in MFN2, from ten families, describing their clinical and genetic characteristics. Evaluated patients presented a variable age of onset and a wide phenotypic spectrum, with most patients presenting a severe phenotype. A novel heterozygous missense variant was detected, p.K357E. It is located at a highly conserved position and predicted as pathogenic by in silico tools. At a clinical level, the p.K357E carrier shows a severe sensorimotor axonal neuropathy. In conclusion, our work expands the genetic spectrum of CMT2A, disclosing a novel mutation and its related clinical effect, and provides a detailed description of the clinical features of a cohort of patients with MFN2 mutations. Obtaining a precise genetic diagnosis in affected families is crucial both for family planning and prenatal diagnosis, and in a therapeutic perspective, as we are entering the era of personalized therapy for genetic diseases.

Efficacy of AAV serotypes to target Schwann cells after intrathecal and intravenous delivery

To optimize gene delivery to myelinating Schwann cells we compared clinically relevant AAV serotypes and injection routes. AAV9 and AAVrh10 vectors expressing either EGFP or the neuropathy-associated gene GJB1/Connexin32 (Cx32) under a myelin specific promoter were injected intrathecally or intravenously in wild type and Gjb1-null mice, respectively. Vector biodistribution in lumbar roots and sciatic nerves was higher in AAVrh10 injected mice while EGFP and Cx32 expression rates and levels were similar between the two serotypes. A gradient of biodistribution away from the injection site was seen with both intrathecal and intravenous delivery, while similar expression rates were achieved despite higher vector amounts injected intravenously. Quantified immune cells in relevant tissues were similar to non-injected littermates. Overall, AAV9 and AAVrh10 efficiently transduce Schwann cells throughout the peripheral nervous system with both clinically relevant routes of administration, although AAV9 and intrathecal injection may offer a more efficient approach for treating demyelinating neuropathies.

AAV9-mediated Schwann cell-targeted gene therapy rescues a model of demyelinating neuropathy

Mutations in the GJB1 gene, encoding the gap junction (GJ) protein connexin32 (Cx32), cause X-linked Charcot-Marie-Tooth disease (CMT1X), an inherited demyelinating neuropathy. We developed a gene therapy approach for CMT1X using an AAV9 vector to deliver the GJB1/Cx32 gene under the myelin protein zero (Mpz) promoter for targeted expression in Schwann cells. Lumbar intrathecal injection of the AAV9-Mpz.GJB1 resulted in widespread biodistribution in the peripheral nervous system including lumbar roots, sciatic and femoral nerves, as well as in Cx32 expression in the paranodal non-compact myelin areas of myelinated fibers. A pre-, as well as post-onset treatment trial in Gjb1-null mice, demonstrated improved motor performance and sciatic nerve conduction velocities along with improved myelination and reduced inflammation in peripheral nerve tissues. Blood biomarker levels were also significantly ameliorated in treated mice. This study provides evidence that a clinically translatable AAV9-mediated gene therapy approach targeting Schwann cells could potentially treat CMT1X.

Challenges in Treating Charcot-Marie-Tooth Disease and Related Neuropathies: Current Management and Future Perspectives

There is still no effective drug treatment available for Charcot-Marie-Tooth neuropathies (CMT). Current management relies on rehabilitation therapy, surgery for skeletal deformities, and symptomatic treatment of pain; fatigue and cramps are frequent complaints that are difficult to treat. The challenge is to find disease-modifying therapies. Several approaches, including gene silencing, to counteract the PMP22 gene overexpression in the most frequent CMT1A type are under investigation. PXT3003 is the compound in the most advanced phase for CMT1A, as a second-phase III trial is ongoing. Gene therapy to substitute defective genes or insert novel ones and compounds acting on pathways important for different CMT types are being developed and tested in animal models. Modulation of the Neuregulin pathway determining myelin thickness is promising for both hypo-demyelinating and hypermyelinating neuropathies; intervention on Unfolded Protein Response seems effective for rescuing misfolded myelin proteins such as P0 in CMT1B. HDAC6 inhibitors improved axonal transport and ameliorated phenotypes in different CMT models. Other potential therapeutic strategies include targeting macrophages, lipid metabolism, and Nav1.8 sodium channel in demyelinating CMT and the P2X7 receptor, which regulates calcium influx into Schwann cells, in CMT1A. Further approaches are aimed at correcting metabolic abnormalities, including the accumulation of sorbitol caused by biallelic mutations in the sorbitol dehydrogenase (SORD) gene and of neurotoxic glycosphingolipids in HSN1.

Mechanisms and Treatments in Demyelinating CMT

Demyelinating forms of Charcot-Marie-Tooth disease (CMT) are genetically and phenotypically heterogeneous and result from highly diverse biological mechanisms including gain of function (including dominant negative effects) and loss of function. While no definitive treatment is currently available, rapid advances in defining the pathomechanisms of demyelinating CMT have led to promising pre-clinical studies, as well as emerging clinical trials. Especially promising are the recently completed pre-clinical genetic therapy studies in PMP-22, GJB1, and SH3TC2-associated neuropathies, particularly given the success of similar approaches in humans with spinal muscular atrophy and transthyretin familial polyneuropathy. This article focuses on neuropathies related to mutations in PMP-22, MPZ, and GJB1, which together comprise the most common forms of demyelinating CMT, as well as on select rarer forms for which promising treatment targets have been identified. Clinical characteristics and pathomechanisms are reviewed in detail, with emphasis on therapeutically targetable biological pathways. Also discussed are the challenges facing the CMT research community in its efforts to advance the rapidly evolving biological insights to effective clinical trials. These considerations include the limitations of currently available animal models, the need for personalized medicine approaches/allele-specific interventions for select forms of demyelinating CMT, and the increasing demand for optimal clinical outcome assessments and objective biomarkers.

Animal Models as a Tool to Design Therapeutical Strategies for CMT-like Hereditary Neuropathies

Since ancient times, animal models have provided fundamental information in medical knowledge. This also applies for discoveries in the field of inherited peripheral neuropathies (IPNs), where they have been instrumental for our understanding of nerve development, pathogenesis of neuropathy, molecules and pathways involved and to design potential therapies. In this review, we briefly describe how animal models have been used in ancient medicine until the use of rodents as the prevalent model in present times. We then travel along different examples of how rodents have been used to improve our understanding of IPNs. We do not intend to describe all discoveries and animal models developed for IPNs, but just to touch on a few arbitrary and paradigmatic examples, taken from our direct experience or from literature. The idea is to show how strategies have been developed to finally arrive to possible treatments for IPNs.

Updated review of therapeutic strategies for Charcot-Marie-Tooth disease and related neuropathies

Introduction: Charcot-Marie-Tooth disease (CMT) and related neuropathies represent the most prevalent inherited neuromuscular disorders. Nonetheless, there is still no pharmacological treatment available for any CMT type. However, the landscape is rapidly evolving and several novel approaches are providing encouraging results in preclinical studies and leading to clinical trials.Areas covered: The authors review the most promising therapies under study and the ongoing/planned clinical trials. Several approaches to address PMP22 overexpression underlying CMT1A, the most frequent subtype, are being tested. Gene silencing, targeting PMP22, and gene therapy, to introduce specific genes or to substitute or modulate defective ones, are being experimented in animal models. Compounds acting on ER stress, unfolded protein response, neuregulin pathways, phosphoinositides metabolism, axonal transport and degeneration, inflammation, polyol pathway, deoxysphingolipid metabolism, purine nucleotide pool are potential therapeutic candidates for different forms of CMT and related neuropathies.Expert opinion: We are getting closer to find effective therapies for CMT, but are far behind the exciting examples of other genetic neuromuscular disorders. The authors analyze the possible reasons for this gap and the way to fill it. Preclinical and clinical research is ongoing with coordinated efforts and they are confident that in the next few years we will see the first effective treatments.

Emerging Therapies for Charcot-Marie-Tooth Inherited Neuropathies

Inherited neuropathies known as Charcot-Marie-Tooth (CMT) disease are genetically heterogeneous disorders affecting the peripheral nerves, causing significant and slowly progressive disability over the lifespan. The discovery of their diverse molecular genetic mechanisms over the past three decades has provided the basis for developing a wide range of therapeutics, leading to an exciting era of finding treatments for this, until now, incurable group of diseases. Many treatment approaches, including gene silencing and gene replacement therapies, as well as small molecule treatments are currently in preclinical testing while several have also reached clinical trial stage. Some of the treatment approaches are disease-specific targeted to the unique disease mechanism of each CMT form, while other therapeutics target common pathways shared by several or all CMT types. As promising treatments reach the stage of clinical translation, optimal outcome measures, novel biomarkers and appropriate trial designs are crucial in order to facilitate successful testing and validation of novel treatments for CMT patients.

Loss of function MPZ mutation causes milder CMT1B neuropathy

Mutations in Myelin Protein Zero (MPZ) cause CMT1B, the second leading cause of CMT1. Many of the >200 mutations cause neuropathy through a toxic gain of function by the mutant protein such as ER retention, activation of the Unfolded Protein Response (UPR) or disruption of myelin compaction. While there is extensive literature on the loss of function consequences of MPZ in heterozygous Mpz +/- null mice, there is little known of the consequences of MPZ haploinsufficiency in humans. We identified six patients from different families with p.Tyr68Ter or p.Asp104fs heterozygous mutations of MPZ that are predicted to cause a premature termination and nonsense mediated decay of the mutant allele. Five patients were evaluated in Milan and one in Iowa City; all should be haploinsufficient for MPZ. Patients were evaluated clinically and by electrophysiology. Sensory ataxia dominated the clinical presentation with only mild weakness present in five of the six patients. Symptoms presented in adulthood in all patients and only one individual had a CMTNSv2 >5. Deep tendon reflexes were absent in all patients. Patients with likely MPZ loss of function due to mutations that cause haplodeficiency in MPZ have a mild, predominantly large fiber sensory neuropathy that serves as a human equivalent to the neuropathy observed in heterozygous Mpz null mice. Successful therapeutic approaches in treating Mpz deficient mice may be candidates for trials in these and similar patients.

AAV2/9-mediated silencing of PMP22 prevents the development of pathological features in a rat model of Charcot-Marie-Tooth disease 1 A

Charcot-Marie-Tooth disease 1 A (CMT1A) results from a duplication of the PMP22 gene in Schwann cells and a deficit of myelination in peripheral nerves. Patients with CMT1A have reduced nerve conduction velocity, muscle wasting, hand and foot deformations and foot drop walking. Here, we evaluate the safety and efficacy of recombinant adeno-associated viral vector serotype 9 (AAV2/9) expressing GFP and shRNAs targeting Pmp22 mRNA in animal models of Charcot-Marie-Tooth disease 1 A. Intra-nerve delivery of AAV2/9 in the sciatic nerve allowed widespread transgene expression in resident myelinating Schwann cells in mice, rats and non-human primates. A bilateral treatment restore expression levels of PMP22 comparable to wild-type conditions, resulting in increased myelination and prevention of motor and sensory impairments over a twelve-months period in a rat model of CMT1A. We observed limited off-target transduction and immune response using the intra-nerve delivery route. A combination of previously characterized human skin biomarkers is able to discriminate between treated and untreated animals, indicating their potential use as part of outcome measures.

The Complex Clinical and Genetic Landscape of Hereditary Peripheral Neuropathy

Hereditary peripheral neuropathy (HPN) is a complex group of neurological disorders caused by mutations in genes expressed by neurons and Schwann cells. The inheritance of a single mutation or multiple mutations in several genes leads to disease phenotype. Patients exhibit symptoms during development, at an early age or later in adulthood. Most of the mechanistic understanding about these neuropathies comes from animal models and histopathological analyses of postmortem human tissues. Diagnosis is often very complex due to the heterogeneity and overlap in symptoms and the frequent overlap between various genes and different mutations they possess. Some symptoms in HPN are common through different subtypes such as axonal degeneration, demyelination, and loss of motor and sensory neurons, leading to similar physiologic abnormalities. Recent advances in gene-targeted therapies, genetic engineering, and next-generation sequencing have augmented our understanding of the underlying pathogenetic mechanisms of HPN.

Development and Validation of the Pediatric Charcot-Marie-Tooth Disease Quality of Life Outcome Measure

OBJECTIVE

Charcot-Marie-Tooth disease (CMT) reduces health-related quality of life (QOL), especially in children. Defining QOL in pediatric CMT can help physicians monitor disease burden clinically and in trials. We identified items pertaining to QOL in children with CMT and conducted validation studies to develop a pediatric CMT-specific QOL outcome measure (pCMT-QOL).

METHODS

Development and validation of the pCMT-QOL patient-reported outcome measure were iterative, involving identifying relevant domains, item pool generation, prospective pilot testing and clinical assessments, structured focus-group interviews, and psychometric testing. Testing was conducted in children with CMT seen at participating sites from the USA, United Kingdom, and Australia.

RESULTS

We conducted systematic literature reviews and analysis of generic QOL measures to identify 6 domains relevant to QOL in children with CMT. Sixty items corresponding to those domains were developed de novo, or identified from literature review and CMT-specific modification of items from the pediatric Neuro-QOL measures. The draft version underwent prospective feasibility and face content validity assessments to develop a working version of the pCMT-QOL measure. From 2010 to 2016, the pCMT-QOL working version was administered to 398 children aged 8 to 18 years seen at the participating study sites of the Inherited Neuropathies Consortium. The resulting data underwent rigorous psychometric analysis, including factor analysis, test-retest reliability, internal consistency, convergent validity, item response theory analysis, and longitudinal analysis, to develop the final pCMT-QOL patient-reported outcome measure.

INTERPRETATION

The pCMT-QOL patient-reported outcome measure is a reliable, valid, and sensitive measure of health-related QOL for children with CMT. ANN NEUROL 2021;89:369-379.

A dysfunctional endolysosomal pathway common to two sub-types of demyelinating Charcot-Marie-Tooth disease

Autosomal dominant mutations in LITAF are responsible for the rare demyelinating peripheral neuropathy, Charcot-Marie-Tooth disease type 1C (CMT1C). The LITAF protein is expressed in many human cell types and we have investigated the consequences of two different LITAF mutations in primary fibroblasts from CMT1C patients using confocal and electron microscopy. We observed the appearance of vacuolation/enlargement of late endocytic compartments (late endosomes and lysosomes). This vacuolation was also observed after knocking out LITAF from either control human fibroblasts or from the CMT1C patient-derived cells, consistent with it being the result of loss-of-function mutations in the CMT1C fibroblasts. The vacuolation was similar to that previously observed in fibroblasts from CMT4J patients, which have autosomal recessive mutations in FIG4. The FIG4 protein is a component of a phosphoinositide kinase complex that synthesises phosphatidylinositol 3,5-bisphosphate on the limiting membrane of late endosomes. Phosphatidylinositol 3,5-bisphosphate activates the release of lysosomal Ca2+ through the cation channel TRPML1, which is required to maintain the homeostasis of endosomes and lysosomes in mammalian cells. We observed that a small molecule activator of TRPML1, ML-SA1, was able to rescue the vacuolation phenotype of LITAF knockout, FIG4 knockout and CMT1C patient fibroblasts. Our data describe the first cellular phenotype common to two different subtypes of demyelinating CMT and are consistent with LITAF and FIG4 functioning on a common endolysosomal pathway that is required to maintain the homeostasis of late endosomes and lysosomes. Although our experiments were on human fibroblasts, they have implications for our understanding of the molecular pathogenesis and approaches to therapy in two subtypes of demyelinating Charcot-Marie-Tooth disease.

Gene Therapy Options as New Treatment for Inherited Peripheral Neuropathy

Inherited peripheral neuropathy (IPN) is caused by heterogeneous genetic mutations in more than 100 genes. So far, several treatment options for IPN have been developed and clinically evaluated using small molecules. However, gene therapy-based therapeutic strategies have not been aggressively investigated, likely due to the complexities of inheritance in IPN. Indeed, because the majority of the causative mutations of IPN lead to gain-of-function rather than loss-of-function, developing a therapeutic strategy is more difficult, especially considering gene therapy for genetic diseases began with the simple idea of replacing a defective gene with a functional copy. Recent advances in gene manipulation technology have brought novel approaches to gene therapy and its clinical application for IPN treatment. For example, in addition to the classically used gene replacement for mutant genes in recessively inherited IPN, other techniques including gene addition to modify the disease phenotype, modulations of target gene expression, and techniques to edit mutant genes have been developed and evaluated as potent therapeutic strategies for dominantly inherited IPN. In this review, the current status of gene therapy for IPN and future perspectives will be discussed.

A Yeast-Based Model for Hereditary Motor and Sensory Neuropathies: A Simple System for Complex, Heterogeneous Diseases

Charcot–Marie–Tooth (CMT) disease encompasses a group of rare disorders that are characterized by similar clinical manifestations and a high genetic heterogeneity. Such excessive diversity presents many problems. Firstly, it makes a proper genetic diagnosis much more difficult and, even when using the most advanced tools, does not guarantee that the cause of the disease will be revealed. Secondly, the molecular mechanisms underlying the observed symptoms are extremely diverse and are probably different for most of the disease subtypes. Finally, there is no possibility of finding one efficient cure for all, or even the majority of CMT diseases. Every subtype of CMT needs an individual approach backed up by its own research field. Thus, it is little surprise that our knowledge of CMT disease as a whole is selective and therapeutic approaches are limited. There is an urgent need to develop new CMT models to fill the gaps. In this review, we discuss the advantages and disadvantages of yeast as a model system in which to study CMT diseases. We show how this single-cell organism may be used to discriminate between pathogenic variants, to uncover the mechanism of pathogenesis, and to discover new therapies for CMT disease.

Defects in Axonal Transport in Inherited Neuropathies

Axonal transport is a highly complex process essential for sustaining proper neuronal functioning. Disturbances can result in an altered neuronal homeostasis, aggregation of cargoes, and ultimately a dying-back degeneration of neurons. The impact of dysfunction in axonal transport is shown by genetic defects in key proteins causing a broad spectrum of neurodegenerative diseases, including inherited peripheral neuropathies. In this review, we provide an overview of the cytoskeletal components, molecular motors and adaptor proteins involved in axonal transport mechanisms and their implication in neuronal functioning. In addition, we discuss the involvement of axonal transport dysfunction in neurodegenerative diseases with a particular focus on inherited peripheral neuropathies. Lastly, we address some recent scientific advances most notably in therapeutic strategies employed in the area of axonal transport, patient-derived iPSC models, in vivo animal models, antisense-oligonucleotide treatments, and novel chemical compounds.

Are we prepared for clinical trials in Charcot-Marie-Tooth disease?

There has been considerable progress in developing treatments for Charcot-Marie-Tooth disease with a number of therapies either completing or nearing clinical trials. In the case of CMT1A, the commonest subtype of CMT, there have been more than five randomised, double blind placebo-controlled trials. Although these trials were negative for the primary outcome measure, considerable lessons have been learnt leading to the collection of large prospective natural history data sets with which to inform future trial design as well as the development of new and sensitive outcome measures. In this review we summarise the difficulties of conducting clinical trials in a slowly progressive disease such as CMT1A and the requirement for sensitive, reproducible and clinically relevant outcome measures. We summarise the current array of CMT specific outcome measures subdivided into clinical outcome measures, functional outcome measures, patient reported outcome measures, biomarkers of disease burden and treatment specific biomarkers of target engagement. Although there is now an array of CMT specific outcome measures, which collectively incorporate clinically relevant, sensitive and reproducible outputs, a single outcome measure incorporating all three qualities remains elusive.

Gene therapy approaches targeting Schwann cells for demyelinating neuropathies

Charcot-Marie-Tooth disease (CMT) encompasses numerous genetically heterogeneous inherited neuropathies, which together are one of the commonest neurogenetic disorders. Axonal CMT types result from mutations in neuronally expressed genes, whereas demyelinating CMT forms mostly result from mutations in genes expressed by myelinating Schwann cells. The demyelinating forms are the most common, and may be caused by dominant mutations and gene dosage effects (as in CMT1), as well as by recessive mutations and loss of function mechanisms (as in CMT4). The discovery of causative genes and increasing insights into molecular mechanisms through the study of experimental disease models has provided the basis for the development of gene therapy approaches. For demyelinating CMT, gene silencing or gene replacement strategies need to be targeted to Schwann cells. Progress in gene replacement for two different CMT forms, including CMT1X caused by GJB1 gene mutations, and CMT4C, caused by SH3TC2 gene mutations, has been made through the use of a myelin-specific promoter to restrict expression in Schwann cells, and by lumbar intrathecal delivery of lentiviral viral vectors to achieve more widespread biodistribution in the peripheral nervous system. This review summarizes the molecular-genetic mechanisms of selected demyelinating CMT neuropathies and the progress made so far, as well as the remaining challenges in the path towards a gene therapy to treat these disorders through the use of optimal gene therapy tools including clinically translatable delivery methods and adeno-associated viral (AAV) vectors.

MiR-506 Targets UHRF1 to Inhibit Colorectal Cancer Proliferation and Invasion via the KISS1/PI3K/NF-κB Signaling Axis

Background

The UHRF1 gene is an epigenetic modification factor that mediates tumor suppressor gene silencing in a variety of cancers. Related studies have reported that UHRF1 can inhibit the expression of the KISS1 gene. However, the regulatory mechanism underlying UHRF1 expression in colorectal cancer (CRC) is still unclear. The aim of this study was to gain a better understanding of the regulation of UHRF1 expression in CRC and to determine whether it regulates the mechanism by which KISS1 promotes CRC metastasis.

Methods

In the present study, the levels of miR-506, UHRF1 and KISS1 expression in CRC tissues and in human CRC cell lines were studied using quantitative real-time PCR (qRT-PCR) and Western blotting. Cell proliferation, migration, and invasion assays are used to detect cell proliferation, migration, and invasion. A dual-luciferase reporter system was used to confirm the target gene of miR-506.

Results

This study found that UHRF1 protein is highly expressed in CRC tissues and negatively correlated with KISS1 protein expression. UHRF1 overexpression activates the PI3K/NF-κB signaling pathway by inhibiting the mRNA expression levels of pathway mediators. Bioinformatics analysis and luciferase reporter gene assays confirmed that miR-506 targets UHRF1.

Conclusion

This study identified the regulation of UHRF1 expression in CRC and the mechanism of CRC metastasis. UHRF1 may be a new potential target molecule for future CRC metastasis treatment.

Charcot-Marie-Tooth: From Molecules to Therapy

Charcot-Marie-Tooth (CMT) is the most prevalent category of inherited neuropathy. The most common inheritance pattern is autosomal dominant, though there also are X-linked and autosomal recessive subtypes. In addition to a variety of inheritance patterns, there are a myriad of genes associated with CMT, reflecting the heterogeneity of this disorder. Next generation sequencing (NGS) has expanded and simplified the diagnostic yield of genes/molecules underlying and/or associated with CMT, which is of paramount importance in providing a substrate for current and future targeted disease-modifying treatment options. Considerable research attention for disease-modifying therapy has been geared towards the most commonly encountered genetic mutations (PMP22, GJB1, MPZ, and MFN2). In this review, we highlight the clinical background, molecular understanding, and therapeutic investigations of these CMT subtypes, while also discussing therapeutic research pertinent to the remaining less common CMT subtypes.