Psychometrics evaluation of Charcot-Marie-Tooth Neuropathy Score (CMTNSv2) second version, using Rasch analysis

Serum neurofilament light chain in hereditary transthyretin amyloidosis: validation in real-life practice

BACKGROUND

Neurofilament light chain (NfL) has emerged as a sensitive biomarker in hereditary transthyretin amyloid polyneuropathy (ATTRv-PN). We hypothesise that NfL can identify conversion of gene carriers to symptomatic disease, and guide treatment approaches.

METHODS

Serum NfL concentration was measured longitudinally (2015-2022) in 59 presymptomatic and symptomatic ATTR variant carriers. Correlations between NfL and demographics, biochemistry and staging scores were performed as well as longitudinal changes pre- and post-treatment, and in asymptomatic and symptomatic cohorts. Receiver-operating analyses were performed to determine cut-off values.

RESULTS

NfL levels correlated with examination scores (CMTNS, NIS and MRC; all p < .01) and increased with disease severity (PND and FAP; all p < .05). NfL was higher in symptomatic and sensorimotor converters, than asymptomatic or sensory converters irrespective of time (all p < .001). Symptomatic or sensorimotor converters were discriminated from asymptomatic patients by NfL concentrations >64.5 pg/ml (sensitivity= 91.9%, specificity = 88.5%), whereas asymptomatic patients could only be discriminated from sensory or sensorimotor converters or symptomatic individuals by a NfL concentration >88.9 pg/ml (sensitivity = 62.9%, specificity = 96.2%) However, an NfL increment of 17% over 6 months could discriminate asymptomatic from sensory or sensorimotor converters (sensitivity = 88.9%, specificity = 80.0%). NfL reduced with treatment by 36%/year and correlated with TTR suppression (r = 0.64, p = .008).

CONCLUSIONS

This data validates the use of serum NfL to identify conversion to symptomatic disease in ATTRv-PN. NfL levels can guide assessment of disease progression and response to therapies.

Axonal excitability as an early biomarker of nerve involvement in hereditary transthyretin amyloidosis

OBJECTIVES

The treatment of hereditary transthyretin amyloidosis polyneuropathy (ATTRv-PN) has been revolutionised by genetic therapies, with dramatic improvements in patient outcomes. Whilst the optimal timing of treatment initiation remains unknown, early treatment is desirable. Consequently, the aim of the study was to develop biomarkers of early nerve dysfunction in ATTRv-PN.

METHODS

Ulnar motor and sensory axonal excitability studies were prospectively undertaken on 22 patients with pathogenic hereditary transthyretin amyloid (ATTRv) gene variants, 12 with large fibre neuropathy (LF+) and 10 without (LF-), with results compared to age- and sex-matched healthy controls.

RESULTS

In motor axons we identified a continuum of change from healthy controls, to LF- and LF+ ATTRv with progressive reduction in hyperpolarising threshold electrotonus (TEh40(10-20 ms): p = 0.04, TEh40(20-40 ms): p = 0.01 and TEh40(90-10 ms): p = 0.01), suggestive of membrane depolarisation. In sensory axons lower levels of subexcitability were observed on single (SubEx) and double pulse (SubEx2) recovery cycle testing in LF+ (SubEx: p = 0.015, SubEx2: p = 0.015, RC(2-1): p = 0.04) suggesting reduced nodal slow potassium conductance, which promotes sensory hyperexcitability, paraesthesia and pain. There were no differences in sensory or motor excitability parameters when comparing different ATTRv variants.

CONCLUSIONS

These progressive changes seen across the disease spectrum in ATTRv-PN suggest that axonal excitability has utility to identify early and progressive nerve dysfunction in ATTRv, regardless of genotype.

SIGNIFICANCE

Axonal excitability is a promising early biomarker of nerve dysfunction in ATTRv-PN.

Lower limb muscle MRI fat fraction is a responsive outcome measure in CMT X1, 1B and 2A

OBJECTIVE

With potential therapies for many forms of Charcot-Marie-Tooth disease (CMT), responsive outcome measures are urgently needed for clinical trials. Quantitative lower limb MRI demonstrated progressive calf intramuscular fat accumulation in the commonest form, CMT1A with large responsiveness. In this study, we evaluated the responsiveness and validity in the three other common forms, due to variants in GJB1 (CMTX1), MPZ (CMT1B) and MFN2 (CMT2A).

METHODS

22 CMTX1, 21 CMT1B and 21 CMT2A patients and matched controls were assessed at a 1-year interval. Intramuscular fat fraction (FF) was evaluated using three-point Dixon MRI at thigh and calf level along with clinical measures including CMT examination score, clinical strength assessment, CMT-HI and plasma neurofilament light chain.

RESULTS

All patient groups had elevated muscle fat fraction at thigh and calf levels, with highest thigh FF and atrophy in CMT2A. There was moderate correlation between calf muscle FF and clinical measures (CMTESv2 rho = 0.405; p = 0.001, ankle MRC strength rho = -0.481; p < 0.001). Significant annualised progression in calf muscle FF was seen in all patient groups (CMTX1 2.0 ± 2.0%, p < 0.001, CMT1B 1.6 ± 2.1% p = 0.004 and CMT2A 1.6 ± 2.1% p = 0.002). Greatest increase was seen in patients with 10-70% FF at baseline (calf 2.7 ± 2.3%, p < 0.0001 and thigh 1.7 ± 2.1%, p = 0.01).

INTERPRETATION

Our results confirm that calf muscle FF is highly responsive over 12 months in three additional common forms of CMT which together with CMT1A account for 90% of genetically confirmed cases. Calf muscle MRI FF should be a valuable outcome measure in upcoming CMT clinical trials.

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.

Initial validation of the Mass. General Neuropathy Exam Tool (MAGNET) for evaluation of distal small-fiber neuropathy

INTRODUCTION/AIMS

Diagnosis of small-fiber neuropathy (SFN) is hampered by its subjective symptoms and signs. Confirmatory testing is insufficiently available and expensive, so predictive examinations have value. However, few support the 2020 SFN consensus-case-definition requirements or were validated for non-diabetes neuropathies. Thus we developed the Massachusetts General Hospital Neuropathy Exam Tool (MAGNET) and measured diagnostic performance in 160 symptomatic patients evaluated for length-dependent SFN from any cause and 37 healthy volunteers.

METHODS

We compared prevalences of abnormalities (vital signs, pupil responses, lower-limb appearance, pin, light touch, vibration and position sensitivity, great-toe strength, muscle stretch reflexes), and validated diagnostic performance against objective SFN tests: lower-leg skin-biopsy epidermal neurite densities and autonomic function testing (AFT). Sensitivity/specificity, feasibility, test-retest and inter-rater reliability, and convergence with the Utah Early Neuropathy Scale were calculated.

RESULTS

Patients' ages averaged 48.5 ± 14.7 years and 70.6% were female. Causes of neuropathy varied, remaining unknown in 59.5%. Among the 46 with abnormal skin biopsies, the most prevalent abnormality was reduced pin sharpness at the toes (71.7%). Inter-rater reliability, test-retest reliability, and convergent validity excelled (range = 91.3-95.6%). Receiver operating characteristics comparing all symptomatic patients versus healthy controls indicated that a MAGNET threshold score of 14 maximized predictive accuracy for skin biopsies (0.74) and a 30 cut-off maximized accuracy for predicting AFT (0.60). Analyzing patients with any abnormal neuropathy-test results identified areas-under-the-curves of 0.87-0.89 for predicting a diagnostic result, accuracy = 0.80-0.89, and Youden's index = 0.62. Overall, MAGNET was 80%-85% accurate for stratifying patients with abnormal versus normal neuropathy test results.

DISCUSSION

MAGNET quickly generates research-quality metrics during clinical examinations.

Peripheral Neuropathy and Decreased Locomotion of a RAB40B Mutation in Human and Model Animals

Rab40 proteins are an atypical subgroup of Rab GTPases containing a unique suppressor of the cytokine signaling (SOCS) domain that is recruited to assemble the CRL5 E3 ligase complex for proteolytic regulation in various biological processes. A nonsense mutation deleting the C-terminal SOCS box in the RAB40B gene was identified in a family with axonal peripheral neuropathy (Charcot-Marie-Tooth disease type 2), and pathogenicity of the mutation was assessed in model organisms of zebrafish and Drosophila. Compared to control fish, zebrafish larvae transformed by the human mutant hRAB40B-Y83X showed a defective swimming pattern of stalling with restricted localization and slower motility. We were consistently able to observe reduced labeling of synaptic markers along neuromuscular junctions of the transformed larvae. In addition to the neurodevelopmental phenotypes, compared to normal hRAB40B expression, we further examined ectopic expression of hRAB40B-Y83X in Drosophila to show a progressive decline of locomotion ability. Decreased ability of locomotion by ubiquitous expression of the human mutation was reproduced not with GAL4 drivers for neuron-specific expression but only when a pan-glial GAL4 driver was applied. Using the ectopic expression model of Drosophila, we identified a genetic interaction in which Cul5 down regulation exacerbated the defective motor performance, showing a consistent loss of SOCS box of the pathogenic RAB40B. Taken together, we could assess the possible gain-of-function of the human RAB40B mutation by comparing behavioral phenotypes in animal models; our results suggest that the mutant phenotypes may be associated with CRL5-mediated proteolytic regulation.

Genetic analysis and natural history of Charcot-Marie-Tooth disease CMTX1 due to GJB1 variants

Charcot-Marie-Tooth disease (CMT) due to GJB1 variants (CMTX1) is the second most common form of CMT. It is an X-linked disorder characterized by progressive sensory and motor neuropathy with males affected more severely than females. Many reported GJB1 variants remain classified as variants of uncertain significance (VUS). In this large, international, multicentre study we prospectively collected demographic, clinical and genetic data on patients with CMT associated with GJB1 variants. Pathogenicity for each variant was defined using adapted American College of Medical Genetics criteria. Baseline and longitudinal analyses were conducted to study genotype-phenotype correlations, to calculate longitudinal change using the CMT Examination Score (CMTES), to compare males versus females, and pathogenic/likely pathogenic (P/LP) variants versus VUS. We present 387 patients from 295 families harbouring 154 variants in GJB1. Of these, 319 patients (82.4%) were deemed to have P/LP variants, 65 had VUS (16.8%) and three benign variants (0.8%; excluded from analysis); an increased proportion of patients with P/LP variants compared with using ClinVar's classification (74.6%). Male patients (166/319, 52.0%, P/LP only) were more severely affected at baseline. Baseline measures in patients with P/LP variants and VUS showed no significant differences, and regression analysis suggested the disease groups were near identical at baseline. Genotype-phenotype analysis suggested c.-17G>A produces the most severe phenotype of the five most common variants, and missense variants in the intracellular domain are less severe than other domains. Progression of disease was seen with increasing CMTES over time up to 8 years follow-up. Standard response mean (SRM), a measure of outcome responsiveness, peaked at 3 years with moderate responsiveness [change in CMTES (ΔCMTES) = 1.3 ± 2.6, P = 0.00016, SRM = 0.50]. Males and females progressed similarly up to 8 years, but baseline regression analysis suggested that over a longer period, females progress more slowly. Progression was most pronounced for mild phenotypes (CMTES = 0-7; 3-year ΔCMTES = 2.3 ± 2.5, P = 0.001, SRM = 0.90). Enhanced variant interpretation has yielded an increased proportion of GJB1 variants classified as P/LP and will aid future variant interpretation in this gene. Baseline and longitudinal analysis of this large cohort of CMTX1 patients describes the natural history of the disease including the rate of progression; CMTES showed moderate responsiveness for the whole group at 3 years and higher responsiveness for the mild group at 3, 4 and 5 years. These results have implications for patient selection for upcoming clinical trials.

Disease-specific wearable sensor algorithms for profiling activity, gait, and balance in individuals with Charcot-Marie-Tooth disease type 1A

BACKGROUND/AIMS

Charcot-Marie-Tooth Disease type 1A (CMT1A), the most common inherited peripheral neuropathy, is characterized by progressive sensory loss and weakness, which results in impaired mobility. Increased understanding of the genetics and pathophysiology of CMT1A has led to development of potential therapeutic agents, necessitating clinical trial readiness. Wearable sensors may provide useful outcome measures for future trials.

METHODS

Individuals with CMT1A and unaffected controls were recruited for this 12-month study. Participants wore sensors for in-clinic assessments and at-home, from which activity, gait, and balance metrics were derived. Mann-Whitney U tests were used to analyze group differences for activity, gait, and balance parameters. Test-retest reliability of gait and balance parameters and correlations of these parameters with clinical outcome assessments (COAs) were examined.

RESULTS

Thirty individuals, 15 CMT1A, and 15 controls, participated. Gait and balance metrics demonstrated moderate to excellent reliability. CMT1A participants had longer step durations (p < .001), shorter step lengths (p = .03), slower gait speeds (p < .001), and greater postural sway (p < .001) than healthy controls. Moderate correlations were found between CMT-Functional Outcome Measure and step length (r = -0.59; p = .02), and gait speed (r = 0.64; p = .01); 11 out of 15 CMT1A participants demonstrated significant increases in stride duration between the first and last quarter of the 6-min walk test, suggesting fatigue.

INTERPRETATION

In this initial study, gait and balance metrics derived from wearable sensors were reliable and associated with COAs in individuals with CMT1A. Larger longitudinal studies are needed to confirm our findings and evaluate sensitivity and utility of these disease-specific algorithms for clinical trial use.

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.

Disease Progression in Charcot-Marie-Tooth Disease Related to MPZ Mutations: A Longitudinal Study

OBJECTIVE

The paucity of longitudinal natural history studies in MPZ neuropathy remains a barrier to clinical trials. We have completed a longitudinal natural history study in patients with MPZ neuropathies across 13 sites of the Inherited Neuropathies Consortium.

METHODS

Change in Charcot-Marie-Tooth Examination Score (CMTES) and Rasch modified CMTES (CMTES-R) were evaluated using longitudinal regression over a 5-year period in subjects with MPZ neuropathy. Data from 139 patients with MPZ neuropathy were examined.

RESULTS

The average baseline CMTES and CMTES-R were 10.84 (standard deviation [SD] = 6.0, range = 0-28) and 14.60 (SD = 7.56, range = 0-32), respectively. A mixed regression model showed significant change in CMTES at years 2-5 (mean change from baseline of 0.87 points at 2 years, p = 0.008). Subgroup analysis revealed greater change in CMTES at 2 years in subjects with axonal as compared to demyelinating neuropathy (mean change of 1.30 points [p = 0.016] vs 0.06 points [p = 0.889]). Patients with a moderate baseline neuropathy severity also showed more notable change, by estimate, than those with mild or severe neuropathy (mean 2-year change of 1.14 for baseline CMTES 8-14 [p = 0.025] vs -0.03 for baseline CMTES 0-7 [p = 0.958] and 0.25 for baseline CMTES ≥ 15 [p = 0.6897]). The progression in patients harboring specific MPZ mutations was highly variable.

INTERPRETATION

CMTES is sensitive to change over time in adult patients with axonal but not demyelinating forms of MPZ neuropathy. Change in CMTES was greatest in patients with moderate baseline disease severity. These findings will inform future clinical trials of MPZ neuropathies. ANN NEUROL 2023;93:563-576.

Magnetic resonance imaging-based lower limb muscle evaluation in Charcot-Marie-Tooth disease type 1A patients and its correlation with clinical data

We aimed to derive comprehensive MRI parameters that reflect intramuscular fat infiltration severity for designated lower extremity levels, based on semiquantitative analyses in Charcot-Marie-Tooth disease type 1A (CMT1A) patients. We reviewed lower extremity MRIs of 116 CMT1A patients. Intramuscular fat infiltration grading using the Mercuri scale was performed for the non-dominant lower extremity at three levels (proximal, mid, and distal) for the thigh and at two levels (proximal and distal) for the lower leg. Based on MRI results, the following parameters were calculated for each level and for entire muscles: fat infiltration proportion (FIP), significant fat infiltration proportion (SigFIP), and severe fat infiltration proportion (SevFIP). The relationships between the MRI parameters and clinical data were evaluated using Spearman’s correlation analysis. FIP, SigFIP, and SevFIP measured for entire muscles significantly correlated with Charcot-Marie-Tooth Neuropathy Score (p < 0.001), functional disability scale (p < 0.001), 10-m walk test time (p = 0.0003, 0.0010, and 0.0011), and disease duration (p < 0.001). Similar correlations were demonstrated for FIP, SigFIP, and SevFIP acquired from the lower leg. Our MRI parameters obtained through semiquantitative analyses of muscles significantly correlated with clinical parameters in CMT1A patients, suggesting their potential applicability as imaging markers for clinical severity.

Peripheral Myelin Protein 22 Gene Mutations in Charcot-Marie-Tooth Disease Type 1E Patients

Duplication and deletion of the peripheral myelin protein 22 (PMP22) gene cause Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP), respectively, while point mutations or small insertions and deletions (indels) usually cause CMT type 1E (CMT1E) or HNPP. This study was performed to identify PMP22 mutations and to analyze the genotype−phenotype correlation in Korean CMT families. By the application of whole-exome sequencing (WES) and targeted gene panel sequencing (TS), we identified 14 pathogenic or likely pathogenic PMP22 mutations in 21 families out of 850 CMT families who were negative for 17p12 (PMP22) duplication. Most mutations were located in the well-conserved transmembrane domains. Of these, eight mutations were not reported in other populations. High frequencies of de novo mutations were observed, and the mutation sites of c.68C>G and c.215C>T were suggested as the mutational hotspots. Affected individuals showed an early onset-severe phenotype and late onset-mild phenotype, and more than 40% of the CMT1E patients showed hearing loss. Physical and electrophysiological symptoms of the CMT1E patients were more severely damaged than those of CMT1A while similar to CMT1B caused by MPZ mutations. Our results will be useful for the reference data of Korean CMT1E and the molecular diagnosis of CMT1 with or without hearing loss.

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.

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.

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.

Phenotypic heterogeneity in patients with NEFL-related Charcot-Marie-Tooth disease

Charcot–Marie–Tooth disease (CMT) is the most common hereditary peripheral neuropathy. Mutations in the neurofilament light polypeptide (NEFL) gene produce diverse clinical phenotypes, including demyelinating (CMT1F), axonal (CMT2E), and intermediate (CMTDIG) neuropathies. From 2005 to 2020, 1,143 Korean CMT families underwent gene sequencing, and we investigated the clinical, genetic, and neuroimaging spectra of NEFL‐related CMT patients. Ten NEFL mutations in 17 families (1.49%) were identified, of which three (p.L312P, p.Y443N, and p.K467N) were novel. Eight de novo cases were identified at a rate of 0.47 based on a cosegregation analysis. The age of onset was ≤3 years in five cases (13.5%). The patients revealed additional features including delayed walking, ataxia, dysphagia, dysarthria, dementia, ptosis, waddling gait, tremor, hearing loss, and abnormal visual evoked potential. Signs of ataxia were found in 26 patients (70.3%). In leg MRI analyses, various degrees of intramuscular fat infiltration were found. All compartments were evenly affected in CMT1F patients. The anterior and anterolateral compartments were affected in CMT2E, and the posterior compartment was affected in CMTDIG. Thus, NEFL‐related CMT patients showed phenotypic heterogeneities. This study's clinical, genetic, and neuroimaging results could be helpful in the evaluation of novel NEFL variants and differential diagnosis against other CMT subtypes.

Intraepineurial fat quantification and cross-sectional area analysis of the sciatic nerve using MRI in Charcot-Marie-Tooth disease type 1A patients

The objectives of this study were to assess the fat fraction (FF) and cross-sectional area (CSA) of the sciatic nerve in Charcot-Marie-Tooth disease type 1A (CMT1A) patients using Dixon-based proton density fat quantification MRI and to elucidate its potential association with clinical parameters. Thigh MRIs of 18 CMT1A patients and 18 age- and sex-matched volunteers enrolled for a previous study were reviewed. Analyses for FF and CSA of the sciatic nerve were performed at three levels (proximal to distal). CSA and FF were compared between the two groups and among the different levels within each group. The relationship between the MRI parameters and clinical data were assessed in the CMT1A patients. The CMT1A patients showed significantly higher FF at level 3 (p = 0.0217) and significantly larger CSA at all three levels compared with the control participants (p < 0.0001). Comparisons among levels showed significantly higher FF for levels 2 and 3 than for level 1 and significantly larger CSA for level 2 compared with level 1 in CMT1A patients. CSA at level 3 correlated positively with the CMT neuropathy score version 2 (CMTNSv2). In conclusion, the sciatic nerve FF of CMT1A patients was significantly higher on level 3 compared with both the controls and the measurements taken on more proximal levels, suggesting the possibility of increased intraepineurial fat within the sciatic nerves of CMT1A patients, with a possible distal tendency. Sciatic nerve CSA at level 3 correlated significantly and positively with CMTNSv2, suggesting its potential value as an imaging marker for clinical severity.

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.

Quantitative assessment of muscle echogenicity in Charcot-Marie-Tooth disease type 1A by automatic thresholding methods

OBJECTIVE

To investigate the utility of automatic thresholding methods for quantitative muscle echogenicity assessment as a marker of disease severity in Charcot-Marie-Tooth disease type 1A (CMT1A).

METHODS

Muscle ultrasound was performed in 15 CMT1A patients and 7 healthy controls. Muscle echogenicity of six limb muscles in each subject was assessed by 16 automatic thresholding methods and conventional grey-scale analysis. Echogenicity of each method in CMT1A patients was compared with that in controls. A correlation between the echogenicity and CMT neuropathy score (CMTNS) was also analysed in CMT1A patients.

RESULTS

Significant differences in mean echogenicity of the 6 muscles between CMT1A patients and controls were found both in grey-scale analysis (p < 0.01) and 11 of the 16 automatic thresholding methods (p < 0.05 in each method). In CMT1A patients, mean echogenicity of the 6 muscles was positively correlated with CMTNS in 8 of the 16 automatic thresholding methods, but not in grey-scale analysis.

CONCLUSION

Automatic thresholding methods can be used to detect the difference in muscle echogenicity between CMT1A patients and controls. Echogenicity parameters correlate with the disease severity.

SIGNIFICANCE

Quantitative muscle echogenicity assessment by automatic thresholding methods shows potential as a surrogate marker of disease progression in CMT1A.

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.

A review and analysis of the clinical literature on Charcot-Marie-Tooth disease caused by mutations in neurofilament protein L

Charcot-Marie-Tooth disease (CMT) is one of the most common inherited neurological disorders and can be caused by mutations in over 100 different genes. One of the causative genes is NEFL on chromosome 8 which encodes neurofilament light protein (NEFL), one of five proteins that co-assemble to form neurofilaments. At least 34 different CMT-causing mutations in NEFL have been reported which span the head, rod, and tail domains of the protein. The majority of these mutations are inherited dominantly, but some are inherited recessively. The resulting disease is classified variably in clinical reports based on electrodiagnostic studies as either axonal (type 2; CMT2E), demyelinating (type 1; CMT1F), or a form intermediate between the two (dominant intermediate; DI-CMTG). In this article, we first present a brief introduction to CMT and neurofilaments. We then collate and analyze the data from the clinical literature on the disease classification, age of onset and electrodiagnostic test results for the various mutations. We find that mutations in the head, rod, and tail domains can all cause disease with early onset and profound neurological impairment, with a trend toward greater severity for head domain mutations. We also find that the disease classification does not correlate with specific mutation or domain. In fact, different individuals with the same mutation can be classified as having axonal, demyelinating, or dominant intermediate forms of the disease. This suggests that the classification of the disease as CMT2E, CMT1F or DI-CMTG has more to do with variable disease presentation than to differences in the underlying disease mechanism, which is most likely primarily axonal in all cases.

MicroRNAs as Biomarkers of Charcot-Marie-Tooth Disease Type 1A

OBJECTIVE

To determine whether microRNAs (miRs) are elevated in the plasma of individuals with the inherited peripheral neuropathy Charcot-Marie-Tooth disease type 1A (CMT1A), miR profiling was employed to compare control and CMT1A plasma.

METHODS

We performed a screen of CMT1A and control plasma samples to identify miRs that are elevated in CMT1A using next-generation sequencing, followed by validation of selected miRs by quantitative PCR, and correlation with protein biomarkers and clinical data: Rasch-modified CMT Examination and Neuropathy Scores, ulnar compound muscle action potentials, and motor nerve conduction velocities.

RESULTS

After an initial pilot screen, a broader screen confirmed elevated levels of several muscle-associated miRNAs (miR1, -133a, -133b, and -206, known as myomiRs) along with a set of miRs that are highly expressed in Schwann cells of peripheral nerve. Comparison to other candidate biomarkers for CMT1A (e.g., neurofilament light) measured on the same sample set shows a comparable elevation of several miRs (e.g., miR133a, -206, -223) and ability to discriminate cases from controls. Neurofilament light levels were most highly correlated with miR133a. In addition, the putative Schwann cell miRs (e.g., miR223, -199a, -328, -409, -431) correlate with the recently described transmembrane protease serine 5 (TMPRSS5) protein biomarker that is most highly expressed in Schwann cells and also elevated in CMT1A plasma.

CONCLUSIONS

These studies identify a set of miRs that are candidate biomarkers for clinical trials in CMT1A. Some of the miRs may reflect Schwann cell processes that underlie the pathogenesis of the disease.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that a set of plasma miRs are elevated in patients with CMT1A.

The impact of symptoms on daily life as perceived by patients with Charcot-Marie-Tooth type 1A disease

Introduction

In Charcot-Marie-Tooth type 1A (CMT1A) patients, daily life is mainly influenced by mobility and ambulation dysfunctions. The aim of our work was to evaluate the perception of disturbances that mostly impact on daily life in CMT1A patients and its difference on the basis of age, gender, disability, and quality of life.

Methods

Forty-one CMT1A patients underwent neurological assessment focused on establishing clinical disability through the Charcot-Marie-Tooth Neuropathy Score (CMTNS) and quality of life through the Short Form-36 (SF-36) questionnaire. We identified from CMT disturbances 5 categories [weakness in lower limbs (WLL), weakness in upper limbs (WUL), skeletal deformities (SD), sensory symptoms (SS), balance (B)] and patients classified the categories from the highest to the lowest impact on daily life (1: highest; 5: lowest). Ranking of the 5 categories, in the overall sample and in the different subgroups (dividing by gender, median of age and disease duration, CMTNS, domains of SF-36), was obtained and differences among subgroups were assessed using a bootstrap approach.

Results

Rank analysis showed that WLL was the most important disturbance on daily life whereas WUL had the lowest impact. In the older CMT1A group, the most important disturbance on daily life was B that was also the most relevant disturbance in patients with a greater disability. SD influenced daily life in younger patients. SS had less impact on daily life, with the exception of patients with a milder disability.

Discussion

Our findings demonstrated that the perception of disturbances that mostly impact on CMT1A patients’ daily life changes over the lifetime and with degree of disability.

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.

Natural history of Charcot-Marie-Tooth disease type 2A: a large international multicentre study

Mitofusin-2 (MFN2) is one of two ubiquitously expressed homologous proteins in eukaryote cells, playing a critical role in mitochondrial fusion. Mutations in MFN2 (most commonly autosomal dominant) cause Charcot-Marie-Tooth disease type 2A (CMT2A), the commonest axonal form of CMT, with significant allelic heterogeneity. Previous, moderately-sized, cross sectional genotype-phenotype studies of CMT2A have described the phenotypic spectrum of the disease, but longitudinal natural history studies are lacking. In this large multicentre prospective cohort study of 196 patients with dominant and autosomal recessive CMT2A, we present an in-depth genotype-phenotype study of the baseline characteristics of patients with CMT2A and longitudinal data (1–2 years) to describe the natural history. A childhood onset of autosomal dominant CMT2A is the most predictive marker of significant disease severity and is independent of the disease duration. When compared to adult onset autosomal dominant CMT2A, it is associated with significantly higher rates of use of ankle-foot orthoses, full-time use of wheelchair, dexterity difficulties and also has significantly higher CMT Examination Score (CMTESv2) and CMT Neuropathy Score (CMTNSv2) at initial assessment. Analysis of longitudinal data using the CMTESv2 and its Rasch-weighted counterpart, CMTESv2-R, show that over 1 year, the CMTESv2 increases significantly in autosomal dominant CMT2A (mean change 0.84 ± 2.42; two-tailed paired t-test P = 0.039). Furthermore, over 2 years both the CMTESv2 (mean change 0.97 ± 1.77; two-tailed paired t-test P = 0.003) and the CMTESv2-R (mean change 1.21 ± 2.52; two-tailed paired t-test P = 0.009) increase significantly with respective standardized response means of 0.55 and 0.48. In the paediatric CMT2A population (autosomal dominant and autosomal recessive CMT2A grouped together), the CMT Pediatric Scale increases significantly both over 1 year (mean change 2.24 ± 3.09; two-tailed paired t-test P = 0.009) and over 2 years (mean change 4.00 ± 3.79; two-tailed paired t-test P = 0.031) with respective standardized response means of 0.72 and 1.06. This cross-sectional and longitudinal study of the largest CMT2A cohort reported to date provides guidance for variant interpretation, informs prognosis and also provides natural history data that will guide clinical trial design.

Clinical and Neuroimaging Features in Charcot-Marie-Tooth Patients with GDAP1 Mutations

Background and Purpose

Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) are known to cause Charcot-Marie-Tooth disease (CMT). These mutations are very rare in most countries, but not in certain Mediterranean countries. The purpose of this study was to identify the clinical and neuroimaging characteristics of Korean CMT patients with GDAP1 mutations.

Methods

Gene sequencing was applied to 1,143 families in whom CMT had been diagnosed from 2005 to 2020. PMP22 duplication was found in 344 families, and whole-exome sequencing was performed in 699 patients. Magnetic resonance imaging (MRI) were obtained using either a 1.5-T or 3.0-T MRI system.

Results

We found ten patients from eight families with GDAP1 mutations: five with autosomal dominant (AD) CMT type 2K (three families with p.R120W and two families with p.Q218E) and three with autosomal recessive (AR) intermediate CMT type A (two families with homozygous p.H256R and one family with p.P111H and p.V219G mutations). The frequency was about 1.0% exclusive of the PMP22 duplication, which is similar to that in other Asian countries. There were clinical differences among AD GDAP1 patients according to mutation sites. Surprisingly, fat infiltrations evident in lower-limb MRI differed between AD and AR patients. The posterior-compartment muscles in the calf were affected early and predominantly in AD patients, whereas AR patients showed fat infiltration predominantly in the anterolateral-compartment muscles.

Conclusions

This is the first cohort report on Korean patients with GDAP1 mutations. The patients with AD and AR inheritance routes exhibited different clinical and neuroimaging features in the lower extremities. We believe that these results will help to expand the knowledge of the clinical, genetic, and neuroimaging features of CMT.

Plasma neurofilament light chain as a potential biomarker in Charcot-Marie-Tooth disease

BACKGROUND AND PURPOSE

Charcot-Marie-Tooth (CMT) disease is a chronic, slowly progressing disorder. The lack of specific disease progression biomarkers limits the execution of clinical trials. However, neurofilament light chain (NfL) has been suggested as a potential biomarker for peripheral nervous system disorders.

METHODS

Ninety-six CMT disease patients and 60 healthy controls were enrolled in the study. Disease severity assessment included clinical evaluation with CMT Neuropathy Score version 2 (CMTNSv2). Blood plasma NfL concentrations were measured using the single-molecule array NfL assay.

RESULTS

The NfL concentration was significantly higher in the CMT disease patient group than in the controls (p < 0.001). Of the CMT disease patients, those with type CMTX1 had a higher NfL level than those in the two other analysed subgroups (CMT1A and other CMT disease types) (p = 0.0498). The NfL concentration had a significant but weak correlation with the CMTNSv2 (r_s  = 0.25, p = 0.012). In one CMT disease patient with an extremely elevated NfL level, overlap with chronic inflammatory demyelinating polyneuropathy was suspected. Receiver operating characteristic analysis showed that an NfL concentration of 8.9 pg/ml could be used to discriminate CMT disease patients from controls, with an area under the curve of 0.881.

CONCLUSIONS

Our study confirmed that the plasma NfL concentration is significantly higher in CMT disease patients than in controls. Plasma NfL concentration was found to significantly, albeit weakly, reflect the clinical severity of CMT disease. In the future, NfL may be used, either individually or collaboratively, as a biomarker in the clinical context of suspected CMT disease; however, several issues need to be addressed first.

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.

Rate of Changes in CMT Neuropathy and Examination Scores in Japanese Adult CMT1A Patients

Introduction: We aimed to clarify when adult patients with Charcot-Marie-Tooth disease type 1A (CMT1A), especially those diagnosed at middle or advanced ages, first showed symptoms and whether the rate of disease progression is accelerated by aging.

Methods: Medical records of CMT1A outpatients between 2012 and 2019 were reviewed. The age at diagnosis, age when symptoms first appeared, and rate of disease progression, assessed based on clinical outcome measures including the CMT Neuropathy Score (CMTNS), Rasch-modified CMTNS (CMTNS-R), CMT Examination Score (CMTES), and Rasch-modified CMTES (CMTES-R) were analyzed.

Results: Among 45 adult CMT1A patients, 42% had been diagnosed after 50 years of age, whereas 91% of all patients had exhibited some CMT-related symptoms before 20 years of age. The annual increase of all clinical outcome measures did not differ between patients under and over 50 years. Even when limited to patients whose initial CMTES-R showed mild to moderate severity, the rate of change in CMTES-R did not differ between the two age groups (the annual mean ± standard deviation, under 50 years: 1.1 ± 1.0, and over 50 years: 0.9 ± 1.1, p = 0.68). To determine whether patients with disabilities at a young age have a higher deterioration rate, they were classified into three groups according to their current age and age at diagnosis: patients under 50 years of age, patients over 50 years of age but diagnosed before 50, and patients diagnosed after 50 years of age. The mean annual increase of all clinical outcome measures, however, did not differ among these groups (CMTES-R: 1.03 ± 1.01 vs. 0.94 ± 1.57 vs. 0.81 ± 0.88, respectively, p = 0.87).

Discussion: CMT1A patients develop symptoms in childhood and adolescence even if such symptoms are not noticeable until reaching an advanced age. Deterioration rates of clinical outcome measures are constant irrespective of the age in their adulthood, although we cannot rule out the limitation that the difference did not reach significance because of the small number of patients. Being aware of the existence of a considerable number of undiagnosed CMT patients will help promote the avoidance of inadequate medication.

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.

Transmembrane protease serine 5: a novel Schwann cell plasma marker for CMT1A

OBJECTIVE

Development of biomarkers for Charcot-Marie-Tooth (CMT) disease is critical for implementing effective clinical trials. The most common form of CMT, type 1A, is caused by a genomic duplication surrounding the PMP22 gene. A recent report (Neurology 2018;90:e518-3524) showed elevation of neurofilament light (NfL) in plasma of CMT1A disease patients, which correlated with disease severity. However, no plasma/serum biomarker has been identified that is specific to Schwann cells, the most directly affected cells in CMT1A.

METHODS

We used the Olink immuno PCR platform to profile CMT1A patient (n = 47, 2 cohorts) and normal control plasma (n = 41, two cohorts) on five different Olink panels to screen 398 unique proteins.

RESULTS

The TMPRSS5 protein (Transmembrane protease serine 5) was elevated 2.07-fold (P = <0.0001) in two independent cohorts of CMT1A samples relative to controls. TMPRSS5 is most highly expressed in Schwann cells of peripheral nerve. Consistent with early myelination deficits in CMT1A, TMPRSS5 was not significantly correlated with disease score (CMTES-R, CMTNS-R), nerve conduction velocities (Ulnar CMAP, Ulnar MNCV), or with age. TMPRSS5 was not significantly elevated in smaller sample sets from patients with CMT2A, CMT2E, CMT1B, or CMT1X. The Olink immuno PCR assays confirmed elevated levels of NfL (average 1.58-fold, P < 0.0001), which correlated with CMT1A patient disease score.

INTERPRETATION

These data identify the first Schwann cell-specific protein that is elevated in plasma of CMT1A patients, and may provide a disease marker and a potentially treatment-responsive biomarker with good disease specificity for clinical trials.

Plasma neurofilament light chain concentration is increased and correlates with the severity of neuropathy in hereditary transthyretin amyloidosis

Hereditary transthyretin amyloidosis (ATTRm) causes a disabling peripheral neuropathy as part of a multisystem disorder. The recent development of highly effective gene silencing therapies has highlighted the need for effective biomarkers of disease activity to guide the decision of when to start and stop treatment. In this study, we measured plasma neurofilament light chain (pNfL) concentration in 73 patients with ATTR and found that pNfL was significantly raised in ATTRm patients with peripheral neuropathy compared to healthy controls. Furthermore, pNFL correlated with disease severity as defined by established clinical outcome measures in patients for whom this information was available. These findings suggest a potential role of pNfL in monitoring disease activity and progression in ATTRm patients.

Development of MRC Centre MRI calf muscle fat fraction protocol as a sensitive outcome measure in Hereditary Sensory Neuropathy Type 1

OBJECTIVES

Hereditary sensory neuropathy type 1 (HSN1) is a rare, slowly progressive neuropathy causing profound sensory deficits and often severe motor loss. L-serine supplementation is a possible candidate therapy but the lack of responsive outcome measures is a barrier for undertaking clinical trials in HSN1. We performed a 12-month natural history study to characterise the phenotype of HSN1 and to identify responsive outcome measures.

METHODS

Assessments included Charcot-Marie-Tooth Neuropathy Score version 2 (CMTNSv2), CMTNSv2-Rasch modified, nerve conduction studies, quantitative sensory testing, intraepidermal nerve fibre density (thigh), computerised myometry (lower limbs), plasma 1-deoxysphingolipid levels, calf-level intramuscular fat accumulation by MRI and patient-based questionnaires (Neuropathic Pain Symptom Inventory and 36-Short Form Health Survey version 2 [SF-36v2]).

RESULTS

35 patients with HSN1 were recruited. There was marked heterogeneity in the phenotype mainly due to differences between the sexes: males generally more severely affected. The outcome measures that significantly changed over 1 year and correlated with CMTNSv2, SF-36v2-physical component and disease duration were MRI determined calf intramuscular fat accumulation (mean change in overall calf fat fraction 2.36%, 95% CI 1.16 to 3.55, p=0.0004), pressure pain threshold on the hand (mean change 40 kPa, 95% CI 0.7 to 80, p=0.046) and myometric measurements of ankle plantar flexion (median change -0.5 Nm, IQR -9.5 to 0, p=0.0007), ankle inversion (mean change -0.89 Nm, 95% CI -1.66 to -0.12, p=0.03) and eversion (mean change -1.61 Nm, 95% CI -2.72 to -0.51, p=0.006). Intramuscular calf fat fraction was the most responsive outcome measure.

CONCLUSION

MRI determined calf muscle fat fraction shows validity and high responsiveness over 12 months and will be useful in HSN1 clinical trials.

Development and validation of the Charcot-Marie-Tooth Disease Infant Scale

Many genetic subtypes of Charcot-Marie-Tooth disease (CMT) show signs of symptomatic disease during the earliest years of life. This might be the ideal time to intervene before progression of clinical sequelae due to demyelination and axonal loss. In the absence of disease-specific clinical trial outcome measures for CMT during infancy and early childhood the aim of this study was to develop and validate a functional measure of disease severity, known as the Charcot-Marie-Tooth disease Infant Scale (CMTInfS). Development projects involved identification of a preliminary pool of 31 items representing the range of disability in affected patients aged 0-4 years from a systematic review of the literature, peer review by 12 expert clinicians and researchers in the field, design of a scoring algorithm and pilot testing in 22 participants. Subsequently, a series of validation projects were conducted based on 128 assessments of: 26 confirmed cases of inherited neuropathy (17 CMT1A, one CMT1B, one CMT1D, one CMT2C, one CMT2S, two CMT4C, one CMTX3, one Riboflavin Transporter Deficiency Type 2, and one unidentified mutation); seven 'at risk' cases and 95 unaffected healthy controls recruited through the NIH-funded Inherited Neuropathies Consortium. Validation projects included: Item, Factor and Rasch analysis, intra- and inter-rater reliability, discriminant ability and convergent validity with the CMT Pediatric Scale (CMTPedS) for children aged 3-4 years. Development and validation projects produced a psychometrically robust 15-item scale. Rasch analysis supported the viability of the CMTInfS as a unidimensional measure of disease severity and showed good overall model fit, no evidence of misfitting items or persons and was well targeted for affected children. The CMTInfS demonstrated high intra-rater reliability [intraclass correlation coefficient (ICC)3,1 0.999, 95% confidence interval 0.996-1.000) and inter-rater reliability (ICC2,1 0.997, 95% confidence interval 0.992-0.999). The CMTInfS was able to discriminate between the CMT group and controls (P = 0.006), and convergent validity demonstrated good agreement between CMTInfS and CMTPedS scores (r = 0.76, P = 0.01). The final version of the CMTInfS requires 20 min to administer and is a reliable and sensitive functional outcome measure for early onset CMT and related neuropathies.10.1093/brain/awy280_video1awy280media15970672819001.

Schwann cell transcript biomarkers for hereditary neuropathy skin biopsies

OBJECTIVE

Charcot-Marie-Tooth (CMT) disease is most commonly caused by duplication of a chromosomal segment surrounding Peripheral Myelin Protein 22, or PMP22 gene, which is classified as CMT1A. Several candidate therapies reduce Pmp22 mRNA levels in CMT1A rodent models, but development of biomarkers for clinical trials in CMT1A is a challenge given its slow progression and difficulty in obtaining nerve samples. Quantitative PCR measurements of PMP22 mRNA in dermal nerves were performed using skin biopsies in human clinical trials for CMT1A, but this approach did not show increased PMP22 mRNA in CMT1A patients compared to controls. One complicating factor is the variable amounts of Schwann cells (SCs) in skin. The objective of the study was to develop a novel method for precise evaluation of PMP22 levels in skin biopsies that can discriminate CMT1A patients from controls.

METHODS

We have developed methods to normalize PMP22 transcript levels to SC-specific genes that are not altered by CMT1A status. Several CMT1A-associated genes were assembled into a custom Nanostring panel to enable precise transcript measurements that can be normalized to variable SC content.

RESULTS

The digital expression data from Nanostring analysis showed reproducible elevation of PMP22 levels in CMT1A versus control skin biopsies, particularly after normalization to SC-specific genes.

INTERPRETATION

This platform should be useful in clinical trials for CMT1A as a biomarker of target engagement that can be used to optimize dosing, and the same normalization framework is applicable to other types of CMT. ANN NEUROL 2019;85:887-898.

Rasch model-based testing of the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire-Chemotherapy-Induced Peripheral Neuropathy (QLQ-CIPN20) using Alliance for Clinical Trials in Oncology (Alliance) A151408 study data

PURPOSE

To test the psychometric properties of the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire-Chemotherapy-Induced Peripheral Neuropathy (QLQ-CIPN20) using Rasch-based methods.

METHODS

A secondary data analysis was performed using pooled QLQ-CIPN20 data from patients (N = 1008) who had participated in any of four multi-site chemotherapy-induced peripheral neuropathy (CIPN) treatment and prevention trials. QLQ-CIPN20 responses were evaluated using a polytomous Rasch partial credit model. Data were assessed for person-item fit using the chi-square statistic, item scaling based on response proportions, threshold ordering using item characteristic curves and logit threshold locations, differential item response (DIF) (i.e., response bias) using likelihood ratio tests, and unidimensionality using cluster analysis.

RESULTS

A statistically significant chi-square test indicated poor fit of the observed to the expected responses. More than 70% of the respondents reported a complete absence of six symptoms, reflecting significant floor effects and poor item scaling. Disordered/non-ordinal or narrow response thresholds were found for 11 of the 20 items. Item responses were significantly different by gender (p < 0.0001) and chemotherapy type (p < 0.0001). Cluster analysis findings suggest that the QLQ-CIPN20 is a unidimensional scale due to the absence of item clusters.

CONCLUSIONS

Rasch model testing revealed psychometric weaknesses that could be addressed by revising the QLQ-CIPN20's problematic items and response options. Alternatively, perhaps the new gold standard CIPN measurement approach in future intervention trials should involve use of only the best items, which would also allow comparisons across previous trials that utilized the QLQ-CIPN20.

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

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

The Charcot-Marie-Tooth Functional Outcome Measure (CMT-FOM)

OBJECTIVE

The purpose of this study was to examine the feasibility, reliability, and convergent validity of the Charcot-Marie-Tooth Functional Outcome Measure (CMT-FOM), a new performance-based measure assessing functional ability in adults with CMT disease.

METHODS

Adults with CMT type 1A (CMT1A) were recruited at the Universities of Rochester and Iowa. Participants were assessed using the CMT-FOM, CMT Exam Score (CMTES), and a symptom report. Test-retest reliability was examined using intraclass correlation coefficients, internal consistency using Cronbach α, and convergent and known-groups validity using Spearman rank analysis and the Mann-Whitney test.

RESULTS

Forty-three individuals (70% women; mean age 41, SD 14.9 years) participated. The CMT-FOM (mean 25.3 ± 8.7, range 12-44/52) was moderately correlated with the CMTES (ρ = 0.62; p < 0.0001) and exhibited acceptable reliability (intraclass correlation coefficient = 0.92) and internal consistency (Cronbach α = 0.81). The CMT-FOM discriminated between participants with clinically mild vs moderate-severe CMT1A. Participants with the mildest CMT1A who demonstrated a floor effect on the CMTES showed functional limitations on the CMT-FOM.

CONCLUSIONS

The CMT-FOM is well tolerated and showed no floor/ceiling effects in an adult CMT1A cohort matching those likely to enter upcoming clinical trials. It appears to be reliable, and our data support convergent and known-groups validity in adults with CMT1A. Longitudinal studies further examining the psychometric properties of the CMT-FOM and its responsiveness to change before its application in therapeutic trials are necessary.

Validation of MRC Centre MRI calf muscle fat fraction protocol as an outcome measure in CMT1A

OBJECTIVE

To translate the quantitative MRC Centre MRI protocol in Charcot-Marie-Tooth disease type 1A (CMT1A) to a second site; validate its responsiveness in an independent cohort; and test the benefit of participant stratification to increase outcome measure responsiveness.

METHODS

Three healthy volunteers were scanned for intersite standardization. For the longitudinal patient study, 11 patients with CMT1A were recruited with 10 patients rescanned at a 12-month interval. Three-point Dixon MRI of leg muscles was performed to generate fat fraction (FF) maps, transferred to a central site for quality control and analysis. Clinical data collected included CMT Neuropathy Score.

RESULTS

Test-retest reliability of FF within individual healthy calf muscles at the remote site was excellent: intraclass correlation coefficient 0.79, limits of agreement -0.67 to +0.85 %FF. In patients, mean calf muscle FF was 21.0% and correlated strongly with disease severity and age. Calf muscle FF significantly increased over 12 months (+1.8 ± 1.7 %FF, p = 0.009). Patients with baseline FF >10% showed a 12-month FF increase of 2.9% ± 1.3% (standardized response mean = 2.19).

CONCLUSIONS

We have validated calf muscle FF as an outcome measure in an independent cohort of patients with CMT1A. Responsiveness is significantly improved by enrolling a stratified patient cohort with baseline calf FF >10%.

Charcot-Marie-Tooth Disease and Other Genetic Polyneuropathies

PURPOSE OF REVIEW

Genetic polyneuropathies are rare and clinically heterogeneous. This article provides an overview of the clinical features, neurologic and electrodiagnostic findings, and management strategies for Charcot-Marie-Tooth disease and other genetic polyneuropathies as well as an algorithm for genetic testing.

RECENT FINDINGS

In the past 10 years, many of the mutations causing genetic polyneuropathies have been identified. International collaborations have led to the development of consortiums that are undertaking careful genotype-phenotype correlations to facilitate the development of targeted therapies and validation of outcome measures for future clinical trials. Clinical trials are currently under way for some genetic polyneuropathies.

SUMMARY

Readers are provided a framework to recognize common presentations of various genetic polyneuropathies and a rationale for current diagnostic testing and management strategies in genetic polyneuropathies.

Outcome measures in the clinical evaluation of ambulatory Charcot-Marie-Tooth 1A subjects

BACKGROUND

The outcome measures (OMs) in clinical trials for Charcot-Marie-Tooth disease (CMT) still represent an issue. A recent study highlighted that three additional clinical OMs, the 10-Meter Walk Test (10MWT), the 9-Hole Peg Test, and foot dorsal flexion dynamometry, further improve discrimination between severely and mildly affected patients. Another study has recently assessed the validity and reliability of the 6-Minute Walk Test (6MWT).

AIM

The aim of this study was to identify the most useful scales in the clinical evaluation of CMT1A patients.

DESIGN

Observational study of the baseline data collected in a multicenter, prospective, randomized, single blind, controlled study to evaluate the efficacy and safety of an innovative rehabilitation protocol based on treadmill training, stretching, respiratory, and proprioceptive exercises (TreSPE study) in CMT1A patients.

SETTING

The outpatient service of the four Italian centers involved, which are specialized in hereditary neuropathies.

POPULATION

Fifty-three subjects with a clinical and genetically confirmed diagnosis of CMT1A.

METHODS

At baseline, in addition to the CMT Neuropathy Score, all subjects underwent walking evaluation (6MWT, 10MWT), balance assessment (Berg Balance Scale [BBS], Short Physical Performance Battery [SPPB]) and a subjective evaluation of quality of life (SF36) and walking ability (Walk12).

RESULTS

Analyzing the baseline data, as expected, we found a strong correlation between walk and balance evaluation, proving the validity of these tests in investigating the functional impairment of CMT1A subjects. Particularly, we found that subjects with better balance control walk at higher speed and perceive less limitations in their physical activities or motor skills. This can be reconducted to the fact that ankle stability depends upon different factors such as anatomy integrity, muscle strength and proprioception.

CONCLUSIONS

We identify the 6MWT, 10MWT, and SPPB as the most useful scales, in addition to the CMTNS, to evaluate the functional impairment of CMT1A patients who retain their walking capability and we suggest the use of SPPB because of its rapidity to assess balance and gait disorders in clinical settings.

CLINICAL REHABILITATION IMPACT

In the clinical practice it is important to evaluate patients comprehensively but rapidly. These outcome measures can help us to correctly assess balance and walking ability in CMT1A patients.

Functional outcome measures for infantile Charcot-Marie-Tooth disease: a systematic review

A functional outcome measure for infants (aged 0-3 years) with Charcot-Marie-Tooth (CMT) disease is needed for upcoming disease-modifying trials. A systematic review of outcome measures for infants with neuromuscular disorders was completed to determine if validated measures were available for the CMT infant population. We assessed 20,375 papers and identified seven functional outcome measures for infants with neuromuscular disorders. Six were developed and validated for spinal muscular atrophy (SMA). There were no CMT-specific outcome measures identified; however, one (motor function measure) assessed a range of neuromuscular disorders including 13 infants and children with CMT. The included studies exhibited "good" face, discriminant, convergent and concurrent validity, and reported excellent intra- and inter-rater reliability. No outcome measure was subjected to item response theory. Studies reported outcome measures comprising of 51 different items assessing six domains of function: reflexive movement, axial movement, limb movement, positioning, gross motor, and fine-motor skills. Scoring of items ranged from 2- to 7-point rating scales; and none were scaled to normative reference values to account for changes in growth and development. The SMA focus of most items is likely to produce ceiling effects and lack sensitivity and responsiveness for within and between types of CMT in infants. Nevertheless, several items across scales assessing distal strength, gross- and fine-motor function, could be included in the development of a composite functional outcome measure for infants with CMT to assess disease-modifying interventions.

Plasma neurofilament light chain concentration in the inherited peripheral neuropathies

OBJECTIVE

To perform a cross-sectional study to determine whether plasma neurofilament light chain (NfL) concentration is elevated in patients with Charcot-Marie-Tooth disease (CMT) and if it correlates with disease severity.

METHODS

Blood samples were collected from 75 patients with CMT and 67 age-matched healthy controls over a 1-year period. Disease severity was measured using the Rasch modified CMT Examination and neuropathy scores. Plasma NfL concentration was measured using an in-house-developed Simoa assay.

RESULTS

Plasma NfL concentration was significantly higher in patients with CMT (median 26.0 pg/mL) compared to healthy controls (median 14.6 pg/mL, p < 0.0001) and correlated with disease severity as measured using the Rasch modified CMT examination (r = 0.43, p < 0.0001) and neuropathy (r = 0.37, p = 0.044) scores. Concentrations were also significantly higher when subdividing patients by genetic subtype (CMT1A, SPTLC1, and GJB1) or into demyelinating or axonal forms compared to healthy controls.

CONCLUSION

There are currently no validated blood biomarkers for peripheral neuropathy. The significantly raised plasma NfL concentration in patients with CMT and its correlation with disease severity suggest that plasma NfL holds promise as a biomarker of disease activity, not only for inherited neuropathies but for peripheral neuropathy in general.

Recent advances in the genetic neuropathies

PURPOSE OF REVIEW

Charcot-Marie-Tooth disease (CMT) is one of the commonest inherited neuromuscular diseases with a population prevalence of 1 in 2500. This review will cover recent advances in the genetics and pathomechanisms of CMT and how these are leading to the development of rational therapies.

RECENT FINDINGS

Pathomechanistic and therapeutic target advances in CMT include the identification of the ErbB receptor signalling pathway as a therapeutic target in CMT1A and pharmacological modification of the unfolded protein response in CMT1B. In CMT2D, due to mutations in glycyl-tRNA synthetase, vascular endothelial growth factor-mediated stimulation of the Nrp1 receptor has been identified as a therapeutic target. Preclinical advances have been accompanied by the publication of large natural history cohorts and the identification of a sensitive biomarker of disease (muscle MRI) that is able to detect disease progression in CMT1A over 1 year.

SUMMARY

Advances in next-generation sequencing technology, cell biology and animal models of CMT are paving the way for rational treatments. The combination of robust natural history data and the identification of sensitive biomarkers mean that we are now entering an exciting therapeutic era in the field of the genetic neuropathies.

Biomarkers predict outcome in Charcot-Marie-Tooth disease 1A

BACKGROUND

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited neuropathy, a debilitating disease without known cure. Among patients with CMT1A, disease manifestation, progression and severity are strikingly variable, which poses major challenges for the development of new therapies. Hence, there is a strong need for sensitive outcome measures such as disease and progression biomarkers, which would add powerful tools to monitor therapeutic effects in CMT1A.

METHODS

We established a pan-European and American consortium comprising nine clinical centres including 311 patients with CMT1A in total. From all patients, the CMT neuropathy score and secondary outcome measures were obtained and a skin biopsy collected. In order to assess and validate disease severity and progression biomarkers, we performed qPCR on a set of 16 animal model-derived potential biomarkers in skin biopsy mRNA extracts.

RESULTS

In 266 patients with CMT1A, a cluster of eight cutaneous transcripts differentiates disease severity with a sensitivity and specificity of 90% and 76.1%, respectively. In an additional cohort of 45 patients with CMT1A, from whom a second skin biopsy was taken after 2-3 years, the cutaneous mRNA expression of GSTT2, CTSA, PPARG, CDA, ENPP1 and NRG1-Iis changing over time and correlates with disease progression.

CONCLUSIONS

In summary, we provide evidence that cutaneous transcripts in patients with CMT1A serve as disease severity and progression biomarkers and, if implemented into clinical trials, they could markedly accelerate the development of a therapy for CMT1A.

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

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

Distribution and genotype-phenotype correlation of GDAP1 mutations in Spain

Mutations in the GDAP1 gene can cause Charcot-Marie-Tooth disease. These mutations are quite rare in most Western countries but not so in certain regions of Spain or other Mediterranean countries. This cross-sectional retrospective multicenter study analyzed the clinical and genetic characteristics of patients with GDAP1 mutations across Spain. 99 patients were identified, which were distributed across most of Spain, but especially in the Northwest and Mediterranean regions. The most common genotypes were p.R120W (in 81% of patients with autosomal dominant inheritance) and p.Q163X (in 73% of autosomal recessive patients). Patients with recessively inherited mutations had a more severe phenotype, and certain clinical features, like dysphonia or respiratory dysfunction, were exclusively detected in this group. Dominantly inherited mutations had prominent clinical variability regarding severity, including 29% of patients who were asymptomatic. There were minor clinical differences between patients harboring specific mutations but not when grouped according to localization or type of mutation. This is the largest clinical series to date of patients with GDAP1 mutations, and it contributes to define the genetic distribution and genotype-phenotype correlation in this rare form of CMT.