The Charcot-Marie-Tooth Health Index: Evaluation of a Patient-Reported Outcome

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.

All hands on deck: The multidisciplinary rehabilitation assessment and management of hand function in persons with neuromuscular disorders

Hand function is important in every aspect of our lives. Across a wide range of neuromuscular disorders-inherited ataxias, motor neuron diseases, polyneuropathies, and myopathies-people can experience losses in hand strength, tone, movement, dexterity, joint range, and sensation. Such changes can adversely affect function and independence in daily activities, reducing participation and quality of life. People with neuromuscular disorders (pwNMD) known to involve the hand should be assessed at regular intervals for changes both clinically and using impairment, performance, function, and patient-reported outcome measures as appropriate. A patient-centered approach to management is recommended, with clinicians partnering with the individual, their caregivers and the interprofessional teams to create personalized solutions that can overcome barriers to participation and best meet the goals of individuals affected by neuromuscular disorders. Management strategies should be multifaceted, and may include exercise, orthoses, assistive devices, technological solutions, environmental or task adaptations, medications, and/or surgery. Exercise recommendations and orthoses should be individualized and evolve based on disease progression, impairments, and functional limitations. While medications and surgery have a small role for specific clinical situations, there is a plethora of assistive and technological solutions to assist with basic and instrumental activities of daily living, work/education, and leisure for pwNMD with reduced hand function. In addition, clinicians should advocate for appropriate accommodations for reduced hand function at work/school, and the development of and adherence to legislation supporting accessibility and inclusion.

Clinical practice guidelines for the diagnosis and management of Charcot-Marie-Tooth disease

INTRODUCTION

Charcot-Marie-Tooth disease (CMT) is classified according to neurophysiological and histological findings, the inheritance pattern, and the underlying genetic defect. The objective of these guidelines is to offer recommendations for the diagnosis, prognosis, follow-up, and treatment of this disease in Spain.

MATERIAL AND METHODS

These consensus guidelines were developed through collaboration by a multidisciplinary panel encompassing a broad group of experts on the subject, including neurologists, paediatric neurologists, geneticists, physiatrists, and orthopaedic surgeons.

RECOMMENDATIONS

The diagnosis of CMT is clinical, with patients usually presenting a common or classical phenotype. Clinical assessment should be followed by an appropriate neurophysiological study; specific recommendations are established for the parameters that should be included. Genetic diagnosis should be approached sequentially; once PMP22 duplication has been ruled out, if appropriate, a next-generation sequencing study should be considered, taking into account the limitations of the available techniques. To date, no pharmacological disease-modifying treatment is available, but symptomatic management, guided by a multidiciplinary team, is important, as is proper rehabilitation and orthopaedic management. The latter should be initiated early to identify and improve the patient's functional deficits, and should include individualised exercise guidelines, orthotic adaptation, and assessment of conservative surgeries such as tendon transfer. The follow-up of patients with CMT is exclusively clinical, and ancillary testing is not necessary in routine clinical practice.

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.

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.

Patient-reported disease burden in the Accelerate Clinical Trials in Charcot-Marie-Tooth Disease Study

BACKGROUND AND AIMS

The Charcot-Marie-Tooth Disease Health Index (CMT-HI) is a disease-specific, patient-reported disease burden measure. As part of an international clinical trial readiness study, individuals with CMT1A (ages 18-75 years) underwent clinical outcome assessments (COAs), including the CMT-HI, to capture their longitudinal perspective on the disease burden.

METHODS

Two hundred and fifteen participants underwent serial COAs including the CMT-HI, CMT Functional Outcome Measure (CMT-FOM), CMT Neuropathy Score (CMTNSv2R), and CMT Exam Score (CMTES/CMTES-R). Correlations between the total and subscale scores for the CMT-HI and other COAs were determined. Changes in the CMT-HI scores over 12 months were assessed using paired t-tests. The minimum clinically important difference (MCID) for the CMT-HI and its subscales were calculated by anchoring to a participant global impression of change scale.

RESULTS

At baseline, CMT1A participants were 44.5 ± 15 years old (range: 18-75) and 58% were women. The mean CMT-HI was 25.7 ± 18.8 (range: 0-91.9; 100 reflecting maximal disease burden). The CMT-HI correlated with the CMT-FOM (r = .54, p < .0001), CMTNSv2R (r = .48, p < .0001), and CMTES/CMTES-R (r = .52/r = .54, p < .0001). Disease burden was greater in women than in men (CMT-HI 29.1 ± 19.1 vs. 21.2 ± 17.3, p = .001). Over 12 months, there was a nonsignificant mean increase in CMT-HI of 0.40 ± 10.0 (n = 189, p = .89). The MCID for the CMT-HI total score was 3.8 points (95% CI: 1.7-5.9).

DISCUSSION

Patient-reported disease burden in CMT1A as measured by the CMT-HI is associated with measures of neurologic impairment and physical functioning. Women reported a higher disease burden than men. These data will inform the design of clinical trials in CMT1A.

The Crohn's Disease-Health Index: Development and Evaluation of a Novel Outcome Measure

OBJECTIVE

We sought to develop and validate the Crohn's Disease-Health Index (CD-HI), a disease-specific, patient-reported outcome measure that serially measures Crohn's disease (CD) symptomatic burden in adults with CD.

BACKGROUND

As therapeutic interventions are tested among patients with CD, responsive outcome measures are needed to track disease progression and therapeutic gain during clinical trials.

PATIENTS AND METHODS

We conducted a national cross-sectional study of individuals with CD to identify the most prevalent and impactful symptoms of CD. The most relevant symptoms were included in the CD-HI. We used factor analysis, qualitative patient interviews, test-retest reliability evaluation, and known group validity testing to evaluate and optimize the CD-HI.

RESULTS

The CD-HI contains 12 subscales that comprehensively measure CD burden using the patient's perspective. Fifteen adults with CD beta tested the CD-HI and found the instrument to be clear, easy to use, and relevant to them. Twenty-three adults with CD participated in an assessment of test-retest reliability, which indicated high reliability of individual questions, subscales, and the full instrument (intraclass correlation coefficient = 0.84 for the full instrument). The CD-HI and its subscales demonstrated a high internal consistency (Cronbach α = 0.98 for the full instrument). The CD-HI distinguished between groups of individuals with CD known to differ in disease severity.

CONCLUSIONS

This research supports the use of the CD-HI as a valid, sensitive, reliable, and relevant patient-reported outcome to determine the multifactorial disease burden of those with CD, assess the relevance and merit of future CD therapies, and support drug labeling claims.

Friedreich Ataxia Caregiver-Reported Health Index: Development of a Novel, Disease-Specific Caregiver-Reported Outcome Measure

Background and Objectives

The Friedreich ataxia (FRDA) scientific community needs access to patient-centered outcome measures that satisfy regulatory guidelines and are capable of tracking clinically meaningful changes in FRDA disease burden. The objective of this research was to develop a novel, disease-specific caregiver-reported outcome measure for use in FRDA research and clinical care.

Methods

In prior work, we conducted qualitative interviews and a cross-sectional study of FRDA caregivers and patients to determine the symptoms of greatest importance to individuals with FRDA. We designed the Friedreich Ataxia Caregiver-Reported Health Index (FACR-HI) to serially measure the symptoms of greatest importance to patients and utilized factor analysis, beta testing, reliability testing, and cross-sectional subgroup analysis to further evaluate and optimize this disease-specific outcome measure.

Results

The FACR-HI was designed to measure total disease burden and disease burden in 18 symptomatic domains. The FACR-HI total score demonstrated high internal consistency (Cronbach's α = 0.98) and test-retest reliability (intraclass correlation coefficient = 0.96). Beta interview participants found the FACR-HI to be highly relevant, comprehensive, and easy to use. FACR-HI total and subscale scores were associated with functional staging for ataxia scores and speech impairment.

Discussion

Initial evaluation of the FACR-HI supports its content validity, test-retest reliability, and construct validity as a caregiver-reported outcome measure for assessing how pediatric individuals with FRDA feel and function. The FACR-HI provides a potential mechanism to quantify changes in multifactorial FRDA disease burden during future clinical trials.

The Limb Girdle Muscular Dystrophy Health Index (LGMD-HI)

Limb girdle muscular dystrophy (LGMD) is a debilitating disease and the fourth most common muscular dystrophy. This study describes the development of the LGMD-Health Index (LGMD-HI). Participants were aged >18 years and recruited from three LGMD registries and GRASP-LGMD consortium. The initial instrument, comprised of 16 thematic subscales and 161 items, underwent expert review resulting in item removal as well as confirmatory factor analysis followed by inter-rater reliability and internal consistency of the subscales. Following expert review, one subscale and 59 items were eliminated. Inter-rater reliability was assessed and five items were removed due to Cohen's kappa <0.5. The final subscales had high internal consistencies with an average Cronbach alpha of 0.92. Test re-test reliability of the final instrument was high (intraclass correlation coefficient=0.97). Known groups validity testing showed a statistically significant difference in LGMD-HI scores amongst subjects based on ambulation status (28.7 vs 50.0, p < 0.0001), but not sex, employment status, or genetic subtype. The final instrument is comprised of 15 subscales and 97 items. The LGMD-HI is a disease-specific, patient-reported outcome measure designed in compliance with published FDA guidelines. This instrument is capable of measuring burden of disease with no significant variation based on LGMD subtype.

Multicenter Validation of the Charcot-Marie-Tooth Functional Outcome Measure

BACKGROUND AND OBJECTIVES

Charcot-Marie-Tooth disease type 1A (CMT1A), caused by a duplication of PMP22, is the most common hereditary peripheral neuropathy. For participants with CMT1A, few clinical trials have been performed; however, multiple therapies have reached an advanced stage of preclinical development. In preparation for imminent clinical trials in participants with CMT1A, we have produced a Clinical Outcome Assessment (COA), known as the CMT-Functional Outcome Measure (CMT-FOM), in accordance with the FDA Roadmap to Patient-Focused Outcome Measurement to capture the key clinical end point of function.

METHODS

Participants were recruited through CMT clinics in the United States (n = 130), the United Kingdom (n = 52), and Italy (n = 32). To derive the most accurate signal with the fewest items to identify a therapeutic response, a series of validation studies were conducted including item and factor analysis, Rasch model analysis and testing of interrater reliability, discriminative ability, and convergent validity.

RESULTS

A total of 214 participants aged 18-75 years with CMT1A (58% female) were included in this study. Item, factor, and Rasch analysis supported the viability of the 12-item CMT-FOM as a unidimensional interval scale of function in adults with CMT1A. The CMT-FOM covers strength, upper and lower limb function, balance, and mobility. The 0-100 point scoring system showed good overall model fit, no evidence of misfitting items, and no person misfit, and it was well targeted for adults with CMT1A exhibiting high inter-rater reliability across a range of clinical settings and evaluators. The CMT-FOM was significantly correlated with the CMT Examination Score (r = 0.643; p < 0.001) and the Overall Neuropathy Limitation Scale (r = 0.516; p < 0.001). Significantly higher CMT-FOM total scores were observed in participants self-reporting daily trips and falls, unsteady ankles, hand tremor, and hand weakness (p < 0.05).

DISCUSSION

The CMT-FOM is a psychometrically robust multi-item, unidimensional, disease-specific COA covering strength, upper and lower limb function, balance, and mobility to capture how participants with CMT1A function to identify therapeutic efficacy.

Clinical and Genetic Aspects of Childhood-Onset Demyelinating Charcot-Marie-Tooth's Disease in Brazil

Charcot-Marie-Tooth's disease (CMT) represents the most common inherited neuropathy. Most patients are diagnosed during late stages of disease course during adulthood. We performed a review of clinical, neurophysiological, and genetic diagnoses of 32 patients with genetically defined childhood-onset demyelinating CMT under clinical follow-up in a Brazilian Center for Neuromuscular Diseases from January 2015 to December 2019. The current mean age was 33.1 ± 18.3 years (ranging from 7 to 71 years) and mean age at defined genetic diagnosis was 36.1 ± 18.3 years. The mean age at onset was 6.1 ± 4.4 years. The most common initial complaint was bilateral pes cavus. The genetic basis included PMP22 duplication (CMT1A) ( n  = 18), GJB1 (CMTX1) ( n  = 5), MPZ (CMT1B) ( n  = 3), FIG4 (CMT4J) ( n  = 3), SH3TC2 (CMT4C) ( n  = 1), PLEKHG5 (CMTRIC) ( n  = 1), and PRX (CMT4F) ( n  = 1). Almost all patients ( n  = 31) presented with moderate or severe compromise in the CMT neuropathy score 2 with the highest values observed in CMT1B. Medical history disclosed obstructive sleep apnea ( n  = 5), aseptic meningitis ( n  = 1/ MPZ ), akinetic-rigid parkinsonism ( n  = 1/ FIG4 ), and overlapping chronic inflammatory demyelinating polyneuropathy ( n  = 1/ MPZ ). Motor conduction block was detected in three individuals ( PMP22 , FIG4 , MPZ ). Acute denervation occurred in seven patients. Nonuniform demyelinating patterns were seen in four individuals (two CMT1A, one CMT1B, and one CMTX1). Abnormal cerebral white matter findings were detected in CMT1A and CMTX1, while hypertrophic roots were seen in CMT1A, CMT1B, and CMTX1. Our study emphasizes a relative oligogenic basis in childhood-onset demyelinating CMT and atypical findings may be observed especially in MPZ , PMP22 , and GJB1 gene variants.

Friedreich's Ataxia-Health Index: Development and Validation of a Novel Disease-Specific Patient-Reported Outcome Measure

Background and Objectives

To develop a valid, disease-specific, patient-reported outcome (PRO) measure for adolescents and adults with Friedreich ataxia (FA) for use in therapeutic trials.

Methods

We conducted semistructured qualitative interviews and a national cross-sectional study of individuals with FA to determine the most prevalent and burdensome symptoms and symptomatic themes to this population. These symptoms and symptomatic themes were included as questions in the first version of the Friedreich's Ataxia-Health Index (FA-HI). We subsequently used factor analysis, beta interviews with 17 individuals with FA, and test-retest reliability assessments with 20 individuals with FA to evaluate, refine, and optimize the FA-HI. Finally, we determined the capability of the FA-HI to differentiate between subgroups of FA participants with varying levels of disease severity.

Results

Participants with FA identified 18 symptomatic themes of importance to be included as subscales in the FA-HI. The FA-HI demonstrates high internal consistency and test-retest reliability, and it was identified by participants as highly relevant, comprehensive, and easy to complete. FA-HI total and subscale scores statistically differentiated between subgroups of participants with varying levels of disease burden.

Discussion

Initial evaluation of the FA-HI supports its validity and reliability as a PRO for assessing how individuals with FA feel and function.

The Facioscapulohumeral Muscular Dystrophy-Health Index: Development and evaluation of a disease-specific outcome measure

INTRODUCTION/AIMS

As promising therapeutic interventions are tested among patients with facioscapulohumeral muscular dystrophy (FSHD), there is a clear need for valid and reliable outcome tools to track disease progression and therapeutic gain in clinical trials and for clinical monitoring. Our aim was to develop and validate the Facioscapulohumeral Muscular Dystrophy-Health Index (FSHD-HI) as a multifaceted patient-reported outcome measure (PRO) designed to measure disease burden in adults with FSHD.

METHODS

Through initial interviews with 20 individuals and a national cross-sectional study with 328 individuals with FSHD, we identified the most prevalent and impactful symptoms in FSHD. The most relevant symptoms were included in the FSHD-HI. We used patient interviews, test-retest reliability evaluation, known groups validity testing, and factor analysis to evaluate and optimize the FSHD-HI.

RESULTS

The FSHD-HI contains 14 subscales that measure FSHD disease burden from the patient's perspective. Fourteen adults with FSHD participated in semistructured beta interviews and found the FSHD-HI to be clear, usable, and relevant to them. Thirty-two adults with FSHD participated in test-retest reliability assessments, which demonstrated the high reliability of the FSHD-HI total score (intraclass correlation coefficient = 0.924). The final FSHD-HI and its subscales also demonstrated a high internal consistency (Cronbach α = 0.988).

DISCUSSION

The FSHD-HI provides researchers and clinicians with a reliable and valid mechanism to measure multifaceted disease burden in patients with FSHD. The FSHD-HI may facilitate quantification of therapeutic effectiveness, as demonstrated by its use as a secondary and exploratory measure in several clinical trials.

Response rates in clinical quality registries and databases that collect patient reported outcome measures: a scoping review

BACKGROUND

Patient Reported Outcome Measures (PROMs) are being increasingly introduced in clinical registries, providing a personal perspective on the expectations and impact of treatment. The aim of this study was to describe response rates (RR) to PROMs in clinical registries and databases and to examine the trends over time, and how they change with the registry type, region and disease or condition captured.

METHODS

We conducted a scoping literature review of MEDLINE and EMBASE databases, in addition to Google Scholar and grey literature. All English studies on clinical registries capturing PROMs at one or more time points were included. Follow up time points were defined as follows: baseline (if available), < 1 year, 1 to < 2 years, 2 to < 5 years, 5 to < 10 years and 10 + years. Registries were grouped according to regions of the world and health conditions. Subgroup analyses were conducted to identify trends in RRs over time. These included calculating average RRs, standard deviation and change in RRs according to total follow up time.

RESULTS

The search strategy yielded 1,767 publications. Combined with 20 reports and four websites, a total of 141 sources were used in the data extraction and analysis process. Following the data extraction, 121 registries capturing PROMs were identified. The overall average RR at baseline started at 71% and decreased to 56% at 10 + year at follow up. The highest average baseline RR of 99% was observed in Asian registries and in registries capturing data on chronic conditions (85%). Overall, the average RR declined as follow up time increased.

CONCLUSION

A large variation and downward trend in PROMs RRs was observed in most of the registries identified in our review. Formal recommendations are required for consistent collection, follow up and reporting of PROMs data in a registry setting to improve patient care and clinical practice. Further research studies are needed to determine acceptable RRs for PROMs captured in clinical registries.

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.

On the path to evidence-based therapy in neuromuscular disorders

Neuromuscular disorders encompass a diverse group of acquired and genetic diseases characterized by loss of motor functionality. Although cure is the goal, many therapeutic strategies have been envisioned and are being studied in randomized clinical trials and entered clinical practice. As in all scientific endeavors, the successful clinical translation depends on the quality and translatability of preclinical findings and on the predictive value and feasibility of the clinical models. This chapter focuses on five exemplary diseases: childhood spinal muscular atrophy (SMA), Charcot-Marie-Tooth (CMT) disorders, chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), acquired autoimmune myasthenia gravis (MG), and Duchenne muscular dystrophy (DMD), to illustrate the progress made on the path to evidenced-based therapy.

Hereditary neuropathy

The hereditary neuropathies, collectively referred as Charcot-Marie-Tooth disease (CMT) and related disorders, are heterogeneous genetic peripheral nerve disorders that collectively comprise the commonest inherited neurological disease with an estimated prevalence of 1:2500 individuals. The field of hereditary neuropathies has made significant progress in recent years with respect to both gene discovery and treatment as a result of next-generation sequencing (NGS) approach. These investigations which have identified over 100 causative genes and new mutations have made the classification of CMT even more challenging. Despite so many different mutated genes, the majority of CMT forms share a similar clinical phenotype, and due to this phenotypic homogeneity, genetic testing in CMT is increasingly being performed through the use of NGS panels. The majority of patients still have a mutation in one the four most common genes (PMP22 duplication-CMT1A, MPZ-CMT1B, GJB1-CMTX1, and MFN2-CMT2A). This chapter focuses primarily on these four forms and their potential therapeutic approaches.

Accelerate Clinical Trials in Charcot-Marie-Tooth Disease (ACT-CMT): A Protocol to Address Clinical Trial Readiness in CMT1A

With therapeutic trials on the horizon for Charcot-Marie-Tooth type 1A (CMT1A), reliable, valid, and responsive clinical outcome assessments and biomarkers are essential. Accelerate Clinical Trials in CMT (ACT-CMT) is an international study designed to address important gaps in CMT1A clinical trial readiness including the lack of a validated, responsive functional outcome measure for adults, and a lack of validated biomarkers for multicenter application in clinical trials in CMT1A. The primary aims of ACT-CMT include validation of the Charcot-Marie-Tooth Functional Outcome Measure, magnetic resonance imaging of intramuscular fat accumulation as a lower limb motor biomarker, and in-vivo reflectance confocal microscopy of Meissner corpuscle sensory receptor density, a sensory biomarker. Initial studies have indicated that these measures are feasible, reliable and valid. A large prospective, multi-site study is necessary to fully validate and examine the responsiveness of these outcome measures in relation to existing outcomes for use in future clinical trials involving individuals with CMT1A. Two hundred 15 adults with CMT1A are being recruited to participate in this prospective, international, multi-center study. Serial assessments, up to 3 years, are performed and include the CMT-FOM, CMT Exam Score-Rasch, Overall Neuropathy Limitations Scale, CMT-Health Index, as well as nerve conduction studies, and magnetic resonance imaging and Meissner corpuscle biomarkers. Correlations using baseline data will be examined for validity. Longitudinal analyses will document the changes in function, intramuscular fat accumulation, Meissner corpuscle sensory receptor density. Lastly, we will use anchor-based and other statistical methods to determine the minimally clinically important change for these clinical outcome assessments and biomarkers in CMT1A. Reliable, and responsive clinical outcome assessments of function and disease progression biomarkers are urgently needed for application in early and late phase clinical trials in CMT1A. The ACT-CMT study protocol will address this need through the prospective, longitudinal, multicenter examination in unprecedented detail of novel and existing clinical outcome assessments and motor and sensory biomarkers, and enhance international clinical trial infrastructure, training and preparedness for future therapeutic trials in CMT and related neuropathies.

The Huntington's Disease Health Index: Initial Evaluation of a Disease-Specific Patient Reported Outcome Measure

BACKGROUND

When developed properly, disease-specific patient reported outcome measures have the potential to measure relevant changes in how a patient feels and functions in the context of a therapeutic trial. The Huntington's Disease Health Index (HD-HI) is a multifaceted disease-specific patient reported outcome measure (PROM) designed specifically to satisfy previously published FDA guidance for developing PROMs for product development and labeling claims.

OBJECTIVE

In preparation for clinical trials, we examine the validity, reliability, clinical relevance, and patient understanding of the Huntington's Disease Health Index (HD-HI).

METHODS

We partnered with 389 people with Huntington's disease (HD) and caregivers to identify the most relevant questions for the HD-HI. We subsequently utilized two rounds of factor analysis, cognitive interviews with fifteen individuals with HD, and test-retest reliability assessments with 25 individuals with HD to refine, evaluate, and optimize the HD-HI. Lastly, we determined the capability of the HD-HI to differentiate between groups of HD participants with high versus low total functional capacity score, prodromal versus manifest HD, and normal ambulation versus mobility impairment.

RESULTS

HD participants identified 13 relevant and unique symptomatic domains to be included as subscales in the HD-HI. All HD-HI subscales had a high level of internal consistency and reliability and were found by participants to have acceptable content, relevance, and usability. The total HD-HI score and each subscale score statistically differentiated between groups of HD participants with high versus low disease burden.

CONCLUSION

Initial evaluation of the HD-HI supports its validity and reliability as a PROM for assessing how individuals with HD feel and function.

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.

A longitudinal and cross-sectional study of plasma neurofilament light chain concentration in Charcot-Marie-Tooth disease

Advances in genetic technology and small molecule drug development have paved the way for clinical trials in Charcot-Marie-Tooth disease (CMT); however, the current FDA-approved clinical trial outcome measures are insensitive to detect a meaningful clinical response. There is, therefore, a need to identify sensitive outcome measures or clinically relevant biomarkers. The aim of this study was to further evaluate plasma neurofilament light chain (NFL) as a disease biomarker in CMT. Plasma NFL was measured using SIMOA technology in both a cross-sectional study of a US cohort of CMT patients and longitudinally over 6 years in a UK CMT cohort. In addition, plasma NFL was measured longitudinally in two mouse models of CMT2D. Plasma concentrations of NFL were increased in a US cohort of patients with CMT1B, CMT1X and CMT2A but not CMT2E compared with controls. In a separate UK cohort, over a 6-year interval, there was no significant change in plasma NFL concentration in CMT1A or HSN1, but a small but significant reduction in patients with CMT1X. Plasma NFL was increased in wild type compared to GARSC201R mice. There was no significant difference in plasma NFL in GARSP278KY compared to wild type mice. In patients with CMT1A, the small difference in cross-sectional NFL concentration vs healthy controls and the lack of change over time suggests that plasma NFL may lack sufficient sensitivity to detect a clinically meaningful treatment response in adulthood.

A Roadmap to Patient Engagement: Facioscapulohumeral Muscular Dystrophy and the ReSolve Clinical Trial

We describe our efforts to overcome barriers to patient engagement in facioscapulohumeral muscular dystrophy (FSHD) and offer a roadmap that can be replicated in other rare neurologic disorders. We implemented an engagement plan during Clinical Trial Readiness to Solve Barriers to Drug Development for FSHD (ReSolve), an 18-month, multisite, observational study of individuals with FSHD. Elements of our engagement plan included conducting focus groups during protocol development, patient involvement on the ReSolve external advisory committee, creation of a patient advisory committee, and collaboration with patient advocacy groups. Patient feedback led to adaptations in the study protocol and to changes in recruitment and retention methods. Patient engagement ensures that the patient voice contributes to multiple aspects of trial design and implementation. Our engagement efforts exemplify how collaboration with patients and families can be accomplished in FSHD and the resultant roadmap process may be replicable in other rare neurologic diseases.

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.

Health-related Quality of Life and Satisfaction with German Health Care Services in Patients with Charcot-Marie-Tooth Neuropathy

BackgroundCharcot-Marie-Tooth (CMT) neuropathies entail a large group of diseases with different gene mutation patterns, which produce heterogeneous phenotypes. Although health-related quality of life (HRQOL) is significantly impaired, a comprehensive assessment of HRQOL in CMT patients in Germany considering phenotypical heterogeneity represented a research gap.ObjectiveThe aim was to assess HRQOL and the satisfaction with health care in CMT patients in Germany.MethodsCMT patients >  15 years with a genetically confirmed CMT subtype were recruited through a national CMT patient registry. HRQOL was assessed using the EQ-5D-5L questionnaire. Furthermore, subjective impairments in daily or work activities and satisfaction with health care were assessed using 4-point scales.ResultsHRQOL in CMT patients (n = 385) was impaired compared to the German population. Most patients reported problems in the dimension mobility (89.6%), pain/discomfort (89.4%) and usual activities (81.0%). Except for patients with hereditary neuropathy with liability to pressure palsy (HNPP), we found no differences in HRQOL between the CMT subtypes. 72.0%of CMT patients were satisfied with available health care services. However, patients reported to expect more CMT-specific knowledge and support as well as easier prescription and cost coverage procedures from health professionals and insurances.ConclusionsThe patient-reported outcomes in the assessed CMT cohort elucidate the need for more specific health care services that also address the heterogeneous phenotypes. Although the assessment has been limited to the German health services setting, insights may be applicable to CMT-specific care in other national settings.

The Spinal Muscular Atrophy Health Index: A novel outcome for measuring how a patient feels and functions

INTRODUCTION

The Spinal Muscular Atrophy Health Index (SMA-HI) is a multifaceted, disease-specific, patient-reported outcome to measure an SMA patient's perception of their disease burden. In preparation for upcoming therapeutic trials, we examine the validity, reliability, and usability of the SMA-HI in adults, teenagers, and children with SMA.

METHODS

Using data from a cross-sectional study of 359 international adult patients with SMA, we identified the most relevant symptoms to include in the SMA-HI. We utilized factor analysis, patient interviews with adults and minors (age 8-15 years), known-group validity testing, and test-retest reliability assessments to evaluate and refine the SMA-HI.

RESULTS

The SMA-HI measures overall disease burden and 15 areas of SMA health. Fifteen adult patients and five patients, age 8 to 15 years, participated in semistructured qualitative interviews and found the SMA-HI to be comprehensive, easily completed, and to have clear meaning. The final SMA-HI and its subscales demonstrated good internal consistency (Cronbach α = 0.77-0.96), high test-retest reliability (intraclass correlation coefficient = 0.60-0.96), and an ability to differentiate between SMA groups with different disease severities affecting areas such as employment and ambulation (P < .0001 for both).

DISCUSSION

This research provides evidence that the SMA-HI is a valid, relevant, and reliable outcome measure to assess multifaceted patient-reported disease burden in older children, teenagers, and adults with SMA. The SMA-HI provides an opportunity for researchers and clinicians to measure a SMA patient's perception of their health and determine relevant changes in response to therapeutic intervention or disease progression.

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.

Validation of the Italian version of the Charcot-Marie-Tooth Health Index

The Charcot-Marie-Tooth Health Index (CMT-HI) is a disease-specific patient-reported outcome measure measuring overall disease burden in Charcot-Marie-Tooth (CMT) patients, designed for natural history studies and clinical trials in English-speaking affected individuals. We developed and validated its Italian Charcot-Marie-Tooth Health Index (I-CMT-HI) version. The questionnaire was translated and culturally adapted from source into Italian by two neurologists experienced in CMT and neuromuscular disorders (NMDs). The two translations were reviewed by a panel of seven experts in CMT and NMD. The provisional version was back-translated into English by a professional translator. The definitive Italian version was developed during a consensus teleconference by the panel and a patient representative from ACMT-Rete. A series of clinically and genetically characterized CMT patients completed the final questionnaire; 11 participated in a test-retest reliability assessment of the instrument. The I-CMT-HI was administered to 30 CMT patients (13 CMT1A, eight CMTX1, two CMT1B, two CMT1E, two CMT2I, one CMT2A, one CMT2N, one distal Hereditary Motor Neuropathy), with test-rest in 11:14 females and 16 males, aged (mean ± SD) 48.0 ± 16.4 years (range 18-81), with CMT Examination Score (CMTES) = 10.0 ± 4.4 (range 2-18). The I-CMT-HI mean total score was 29.4 ± 21.2 (range 0.1-60.3). The I-CMT-HI showed a high test-retest reliability: intraclass correlation coefficient = 0.95 (95% confidence interval, 0.84-0.99). No patient had difficulty in completing the questionnaire and none reported any problem with the questions' formulation. The total CMT-HI score was positively correlated with age and CMTES, with higher disease burden with increasing age and disease severity according to the CMTES. The I-CMT-HI is now ready for use in clinical studies in the Italian population.

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.

A longitudinal study of CMT1A using Rasch analysis based CMT neuropathy and examination scores

OBJECTIVE

To evaluate the sensitivity of Rasch analysis-based, weighted Charcot-Marie-Tooth Neuropathy and Examination Scores (CMTNS-R and CMTES-R) to clinical progression in patients with Charcot-Marie-Tooth disease type 1A (CMT1A).

METHODS

Patients with CMT1A from 18 sites of the Inherited Neuropathies Consortium were evaluated between 2009 and 2018. Weighted CMTNS and CMTES modified category responses were developed with Rasch analysis of the standard scores. Change from baseline for CMTNS-R and CMTES-R was estimated with longitudinal regression models.

RESULTS

Baseline CMTNS-R and CMTES-R scores were available for 517 and 1,177 participants, respectively. Mean ± SD age of participants with available CMTES-R scores was 41 ± 18 (range 4-87) years, and 56% were female. Follow-up CMTES-R assessments at 1, 2, and 3 years were available for 377, 321, and 244 patients. A mixed regression model showed significant change in CMTES-R score at years 2 through 6 compared to baseline (mean change from baseline 0.59 points at 2 years, p = 0.0004, n = 321). Compared to the original CMTES, the CMTES-R revealed a 55% improvement in the standardized response mean (mean change/SD change) at 2 years (0.17 vs 0.11). Change in CMTES-R at 2 years was greatest in mildly to moderately affected patients (1.48-point mean change, 95% confidence interval 0.99-1.97, p < 0.0001, for baseline CMTES-R score 0-9).

CONCLUSION

The CMTES-R demonstrates change over time in patients with CMT1A and is more sensitive than the original CMTES. The CMTES-R was most sensitive to change in patients with mild to moderate baseline disease severity and failed to capture progression in patients with severe CMT1A.

CLINICALTRIALSGOV IDENTIFIER

NCT01193075.