Variability between Different Hand-Held Dynamometers for Measuring Muscle Strength.

Muscle strength is routinely measured in patients with neuromuscular disorders by hand-held dynamometry incorporating a wireless load cell to evaluate disease severity and therapeutic efficacy, with magnitude of effect often based on normative reference values. While several hand-held dynamometers exist, their interchangeability is unknown which limits the utility of normative data. We investigated the variability between six commercially available dynamometers for measuring the isometric muscle strength of four muscle groups in thirty healthy individuals. Following electro-mechanical sensor calibration against knowns loads, Citec, Nicholas, MicroFET2, and Commander dynamometers were used to assess the strength of ankle dorsiflexors, hip internal rotators, and shoulder external rotators. Citec, Jamar Plus, and Baseline Hydraulic dynamometers were used to capture hand grip strength. Variability between dynamometers was represented as percent differences and statistical significance was calculated with one-way repeated measures ANOVA. Percent differences between dynamometers ranged from 0.2% to 16%. No significant differences were recorded between the Citec, Nicholas, and MicroFET2 dynamometers (p > 0.05). Citec grip strength measures differed to the Jamar Plus and Baseline Hydraulic dynamometers (p < 0.01). However, when controlling for grip circumference, they were comparable (p > 0.05). Several hand-held dynamometers can be used interchangeably to measure upper and lower limb strength, thereby maximising the use of normative reference values.

Development of a functional outcome measure for riboflavin transporter deficiency.

BACKGROUND AND AIMS: Riboflavin transporter deficiency (RTD) is a progressive inherited neuropathy of childhood onset, characterised clinically by pontobulbar palsy, sensory ataxia, sensorineural deafness, muscle weakness, optic atrophy and respiratory failure. A robust and responsive functional outcome measure is essential for future clinical trials of disease-modifying therapies including genetic therapies. The Charcot-Marie-Tooth disease Pediatric Scale (CMTPedS) is a well-validated outcome measure for CMT and related neuropathies, and might have utility for measuring disease progression in individuals with RTD. However, the CMTPedS requires modifications to account for phenotypic differences between children with CMT and RTD. The aim of this study was to develop a functional outcome measure based on the CMTPedS for specific use in individuals with RTD. METHODS: The CMTPedS data collected over the last 10 years in individuals with RTD attending the Peripheral Neuropathy Management Clinic at the Children's Hospital at Westmead (Sydney, Australia) were reviewed to evaluate each item within the CMTPedS. A literature review of articles published until September 2021 for functional outcome measures generated an item pool for pilot testing. The results of this pilot testing, alongside analysis of existing CMTPedS item scores in the RTD cohort, informed the modification of the CMTPedS. RESULTS: CMTPedS data were reviewed for eight individuals over the past 10 years. Two items were identified as requiring modification or removal and additional items of proximal strength and function needed to be considered. Six studies were identified in the literature review, and five items were selected for pilot testing. 'Shoulder internal rotation' and the '30-s sit to stand test' were added as proximal measures of strength and function. The composite balance item comprising nine tasks in the CMTPedS showed a ceiling effect and was replaced with the single 'Feet apart on a line eyes open' balance item. 'Pinprick sensation' was removed due to a floor effect. INTERPRETATION: This study provides preliminary evidence that the Riboflavin Transporter Deficiency Pediatric Scale (RTDPedS) is a functional outcome measure covering strength, upper and lower limb function, balance and mobility for individuals with RTD to assess disease severity and progression in clinical trials and cohort studies.

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.

Benefit of high-dose oral riboflavin therapy in riboflavin transporter deficiency.

Riboflavin transporter deficiency (RTD) is a progressive inherited neuropathy of childhood onset, characterised by pontobulbar palsy, sensorineural deafness, sensory ataxia, muscle weakness, optic atrophy and respiratory failure. Riboflavin supplementation is beneficial in short-term reports, but the quantum of benefit in various clinical domains is not well understood. A PubMed search was conducted, which identified 94 genetically confirmed cases of RTD who received riboflavin supplementation and had follow-up assessments. Information on the clinical and functional status before and after riboflavin supplementation was collected and analysed. Seventy-six of the 94 patients (80.9%) showed an overall improvement after riboflavin supplementation, and the remaining (19.1%) were stable, though some patients had deteriorations in individual domains with no reported deaths. The domains that had the highest rates of response to riboflavin supplementation were gross motor function (93.3% improved), bulbar palsy (91.3%) and ataxia (90.0%). Improvements were also seen in limb muscle weakness, audiology, facial nerve palsy and respiratory function. Despite treatment, many patients required assistance to ambulate and had severe or profound hearing loss and some remained gastrostomy or tracheostomy dependent. Riboflavin supplementation is a lifesaving intervention for patients with RTD and results in a profound improvement in several functional domains, with early diagnosis and treatment further improving outcomes. Despite treatment, patients are left with residual disability. There is a need to accurately measure functional outcomes in children with RTD and develop additional disease-modifying therapies.

Association of Body Mass Index With Disease Progression in Children With Charcot-Marie-Tooth Disease.

BACKGROUND AND OBJECTIVES: The aim of this study was to evaluate the impact of body mass index (BMI) on disease progression over 2 years in children with Charcot-Marie-Tooth disease (CMT). METHODS: BMI was classified in 242 participants aged 3-20 years with CMT enrolled in the Inherited Neuropathy Consortium, using the International Obesity Task Force (based on adult BMI values, kg/m2) criteria. Groups were categorized as severely underweight (BMI <17 kg/m2), underweight (BMI ≥17 to <18.5 kg/m2), healthy weight (BMI ≥18.5 to <25 kg/m2), overweight (BMI ≥25 to <30 kg/m2), and obese (BMI ≥30 kg/m2). Disease severity was assessed using the CMT Pediatric Scale (CMTPedS), a clinical outcome assessment of disability (0-44 points, mild to severe). RESULTS: At baseline, compared with individuals being of a healthy weight (mean CMTPedS 15.48, SD 9.22), children who were severely underweight (mean CMTPedS difference 9.03, 95% CI 0.94-17.12; p = 0.02), underweight (mean CMTPedS difference 5.97, 95% CI 0.62-11.31; p = 0.02), or obese (mean CMTPedS difference 7.96, 95% CI 1.03-14.88; p = 0.015) exhibited greater disability. At 2 years, compared with individuals being of a healthy weight (mean CMTPedS 17.53, SD 9.41), children who were severely underweight exhibited greater disability (mean CMTPedS difference 9.27, 95% CI 0.90-17.64; p = 0.02). Over the 2-year periods, the mean CMTPedS for the whole sample deteriorated by 1.72 points (95% CI 1.09-2.38; p < 0.001), with severely underweight children progressing at the fastest rate (mean CMTPedS change of 2.3, 95% CI 1.53-6.13; p = 0.21). In children who did not have a change in BMI categories over 2 years (69% of sample), CMTPedS scores deteriorated faster in those who were severely underweight (mean CMTPedS change 6.40 points, 95% CI 2.42-10.38; p = 0.01) than those of healthy weight (mean CMTPedS change 1.79 points, 95% CI 0.93-2.69; p < 0.001). For children who changed BMI categories (31% of sample), CMTPedS scores deteriorated faster in children who became overweight/obese (mean CMTPedS change 2.76 points, 95% CI 0.11-5.41; p = 0.031). DISCUSSION: Children with CMT who were severely underweight, underweight, or obese exhibited greater disability at baseline. Over the 2-year period in those whose BMI remained stable, severely underweight children deteriorated at the fastest rate. For children who changed BMI categories over the 2 years, CMTPedS scores deteriorated faster in children who became overweight/obese. Interventions that maintain or improve BMI toward healthy weight may reduce disability in children with CMT.

Association Between Body Mass Index and Disability in Children With Charcot-Marie-Tooth Disease.

BACKGROUND AND OBJECTIVES: This study examined the association between body mass index (BMI) and disability in children with Charcot-Marie-Tooth disease (CMT). METHODS: We conducted a cross-sectional analysis of 477 patients with CMT who were 3 to 20 years of age from the Inherited Neuropathy Consortium and 316 age- and sex-matched healthy children from the 1,000 Norms Project. BMI was categorized according to the International Obesity Task Force (IOTF) criteria, and BMI categorization was compared with healthy children. IOTF categories (adult equivalent BMI cut points) were severely underweight (BMI <17 kg/m2), underweight (BMI ≥17-<18.5 kg/m2), healthy weight (BMI ≥18.5-<25 kg/m2), overweight (BMI ≥25-<30 kg/m2), and obese (BMI ≥30 kg/m2). Scores on the 0 to 44-point CMT Pediatric Scale (CMTPedS), a well-validated measure of disability, were examined in relation to BMI. RESULTS: There was a higher proportion of children with CMT categorized as severely underweight (5.7% vs 0.3%), underweight (10.3% vs 5.1%), and obese (7.3% vs 3.8%) (p < 0.05). Fewer children with CMT were categorized as healthy weight (61.8% vs 74.4%) (p < 0.05), and the proportion of overweight (14.9% vs 16.5%) between groups was similar. CMTPedS scores (mean ± SD) for weight categories were as follows: severely underweight 27 ± 9, underweight 20 ± 8, healthy weight 17 ± 9, overweight 17 ± 9, and obese 22 ± 10. Compared to children with a healthy weight with CMT, being severely underweight was associated with being more disabled (p < 0.001), as was being obese (p = 0.015). DISCUSSION: The proportion of children with CMT who are underweight or obese is higher compared to age- and sex-matched healthy children. In children with CMT, being underweight or obese is associated with greater disability, when compared to children with CMT of healthy weight.

Diminished muscle oxygen uptake and fatigue in spinal muscular atrophy.

OBJECTIVE: To estimate muscle oxygen uptake and quantify fatigue during exercise in ambulatory individuals with spinal muscular atrophy (SMA) and healthy controls. METHODS: Peak aerobic capacity (VO2peak ) and workload (Wpeak ) were measured by cardiopulmonary exercise test (CPET) in 19 ambulatory SMA patients and 16 healthy controls. Submaximal exercise (SME) at 40% Wpeak was performed for 10 minutes. Change in vastus lateralis deoxygenated hemoglobin, measured by near-infrared spectroscopy, determined muscle oxygen uptake (ΔHHb) at rest and during CPET and SME. Dual energy X-ray absorptiometry assessed fat-free mass (FFM%). Fatigue was determined by percent change in workload or distance in the first compared to the last minute of SME (FatigueSME ) and six-minute walk test (Fatigue6MWT ), respectively. RESULTS: ΔHHb-PEAK, ΔHHb-SME, VO2peak , Wpeak , FFM%, and 6MWT distance were lower (P < 0.001), and Fatigue6MWT and FatigueSME were higher (P < 0.001) in SMA compared to controls. ΔHHb-PEAK correlated with FFM% (r = 0.50) and VO2peak (r = 0.41) only in controls. Only in SMA, Fatigue6MWT was inversely correlated with Wpeak (r = -0.69), and FatigueSME was inversely correlated with FFM% (r = -0.55) and VO2peak (r = -0.69). INTERPRETATION: This study provides further support for muscle mitochondrial dysfunction in SMA patients. During exercise, we observed diminished muscle oxygen uptake but no correlation with aerobic capacity or body composition. We also observed increased fatigue which correlated with decreased aerobic capacity, workload, and body composition. Understanding the mechanisms underlying diminished muscle oxygen uptake and increased fatigue during exercise in SMA may identify additional therapeutic targets that rescue symptomatic patients and mitigate their residual disease burden.

Reliability of the Charcot-Marie-Tooth functional outcome measure.

The CMT-FOM is a 13-item clinical outcome assessment (COA) that measures physical ability in adults with Charcot-Marie-Tooth disease (CMT). Test-retest reliability, internal consistency and convergent validity have been established for the CMT-FOM. This current study sought to establish inter-rater reliability. Following an in-person training of six international clinical evaluators we recruited 10 participants with genetically diagnosed CMT1A, (aged 18-74 years, 6 female). Participants were evaluated using the CMT-FOM over 2 days. Participants were given at least a 3 hour rest between evaluations, and were assessed twice each day. Following the provision of training by master trainers, all 13 items of the CMT-FOM exhibited excellent inter-rater reliability for raw scores (ICC1,1 0.825-0.989) and z-scores (ICC1,1 0.762-0.969). Reliability of the CMT-FOM total score was excellent (ICC1,1 0.983, 95% CI 0.958-0.995). The CMT-FOM is a reliable COA used by clinical evaluators internationally. The next steps are to establish further validation through psychometric evaluation of the CMT-FOM in the Accelerate Clinical Trials in CMT (ACT-CMT) study.

Refining clinical trial inclusion criteria to optimize the standardized response mean of the CMTPedS.

The CMT Pediatric Scale (CMTPedS) is a reliable, valid, and responsive clinical outcome measure of disability in children with CMT. The aim of this study was to identify the most responsive patient subset(s), based on the standardized response mean (SRM), to optimize the CMTPedS as a primary outcome measure for upcoming clinical trials. Analysis was based on a 2-year natural history data from 187 children aged 3-20 years with a range of CMT genetic subtypes. Subsets based on age (3-8 years), disability level (CMTPedS score 0-14), and CMT type (CMT1A) increased the SRM of the CMTPedS considerably. Refining the inclusion criteria in clinical trials to younger, mildly affected cases of CMT1A optimizes the responsiveness of the CMTPedS.

Limitations of 6-minute walk test reference values for spinal muscular atrophy.

INTRODUCTION: The 6-minute walk test (6MWT) is a well-established clinical assessment of functional endurance, validated as a measure of walking ability in spinal muscular atrophy (SMA). The current availability of disease-modifying therapies for SMA indicates a growing need for normative reference data to compare SMA patients with healthy controls. METHODS: The literature was searched in two scientific databases. Studies were evaluated and selected based on adherence to American Thoracic Society guidelines for administering the 6MWT. Reference equations from the selected studies were applied to 6MWT data collected from SMA patients to calculate and compare % predicted values. RESULTS: Three pediatric and six adult studies were selected for comparison. The % predicted values using the pediatric and adult equations ranged from 47.7 ± 18.2% to 67.6 ± 26.2% and 43.0 ± 17.9% to 59.5 ± 26.2%, respectively, and were significantly different (P < 0.001). DISCUSSION: Results suggest significant variability between % predicted values derived from published reference equations in children and adults, despite adherence to 6MWT standardization.

Surgical outcomes of cavovarus foot deformity in children with Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth disease (CMT) causes disabling cavovarus foot deformity. Orthopaedic surgery is performed in severe cases; however few studies have investigated whether surgery improves health outcomes during childhood. This study investigated the impact of cavovarus surgery on validated physical, functional, parent/self-reported and biomechanical measures in 21 consecutive patients (mean age at surgery 12.5 years, SD 2.7) evaluated before and after surgery (mean duration 15.7 months, SD 5.9), and compared to natural history data from 206 children with CMT. Measures from the CMT Pediatric Scale evaluated foot alignment (Foot Posture Index), ankle flexibility (lunge test), strength (foot dorsiflexion/plantarflexion by hand-held dynamometry), function (balance, long jump, 6-minute walk test) and self-reported symptoms. Quality of life (Child Health Questionnaire) and gait (pressure loading) were also assessed. Foot Posture Index and lunge improved with surgery by 6.0 points (SD 3.2) and 6.1° (SD 7.3) respectively (p< 0.01), and differed to the natural course of the disease (p< 0.005). Self-reported daily trips/falls reduced from 60% to 13% (p = 0.016). Pressure improved beneath the rearfoot and midfoot (p = 0.043). Surgery had no effect on strength, function or quality of life, which generally mirrored the natural course. Cavovarus surgery improved foot alignment, ankle flexibility and self-reported trips/falls in children with CMT.

Magnetic resonance imaging of the anterior compartment of the lower leg is a biomarker for weakness, disability, and impaired gait in childhood Charcot-Marie-Tooth disease.

INTRODUCTION: Biomarkers of disease severity in Charcot-Marie-Tooth disease (CMT) are required to evaluate early responses to treatment. In this study we used magnetic resonance imaging (MRI) to evaluate the relationship between muscle volume and intramuscular fat accumulation with weakness, disability, and impaired gait in affected children and adolescents. METHODS: Fifty-five participants underwent MRI of the anterior compartment of the lower leg. Muscle and fat volumes were calculated. Strength was measured using hand-held dynamometry, disability using the CMT Pediatric Scale, and 3-dimensional gait analysis using an 8-camera Vicon Nexus motion capture system. RESULTS: Lower muscle volume was significantly associated with reduced dorsiflexion strength, increased disability, impaired gait profile score, and foot drop. Intramuscular fat accumulation was associated with reduced dorsiflexion strength and impaired gait profile score. DISCUSSION: The MRI protocol described was feasible, reliable, and sensitive to the magnitude of weakness, disability, and walking difficulties in children with CMT. Muscle Nerve 59:213-217, 2019.

Established and novel measures of upper limb impairment in children with Charcot-Marie-tooth disease type 1A and riboflavin transporter deficiency type 2.

Hand function is a problem in patients with Charcot-Marie-Tooth disease type 1A (CMT1A) and Riboflavin Transporter Deficiency type 2 (RTD2). However, a detailed understanding of upper limb involvement in these conditions is lacking. The aim of this pilot study was to compare hand and upper limb function between children with CMT1A, RTD2 and healthy controls using established and novel outcome measures. Three age-and sex-matched groups of four children (5-15 years, 1 male/group) with CMT1A, RTD2, and healthy controls were assessed for function, strength, and sensation. Fatigue and muscle activity of the FDI was also assessed using a submaximal contraction at 40% of the participants' maximal voluntary contraction. Functional measures were most affected in children with RTD2 followed by children with CMT1A, compared to healthy controls. Strength was similarly impaired in CMT1A and RTD2 compared to controls (p < 0.05). Sensation was significantly impaired in RTD2 compared to CMT1A and controls (p = 0.008). While time to fatigue did not differ between groups, a decline in muscle activity while force remained constant showed that controls compensated with other muscles during the fatigue task while children with CMT1A and RTD2 did not have this compensatory ability. Children with CMT1A and RTD2 exhibited marked hand/upper limb impairment. These results suggest the upper limb should be a focus of rehabilitative therapy in affected children using sensitive outcome measures of strength and sensation, as well as functional activities of daily living, which are most relevant to the patient.

Natural history of Charcot-Marie-Tooth disease during childhood.

OBJECTIVE: To determine the rate of disease progression in a longitudinal natural history study of children with Charcot-Marie-Tooth (CMT) disease. METHODS: Two hundred six (103 female) participants aged 3 to 20 years enrolled in the Inherited Neuropathies Consortium were assessed at baseline and 2 years. Demographic, anthropometric, and diagnostic information were collected. Disease progression was assessed with the CMT Pediatric Scale (CMTPedS), a reliable Rasch-built linearly weighted disability scale evaluating fine and gross motor function, strength, sensation, and balance. RESULTS: On average, CMTPedS Total scores progressed at a rate of 2.4 ± 4.9 over 2 years (14% change from baseline; p < 0.001). There was no difference between males and females (mean difference, 0.5; 95% confidence interval [CI], -0.9 to 1.9; p = 0.49). The most responsive CMTPedS items were dorsiflexion strength (z-score change, -0.3; 95% CI, -0.6 to -0.05; p = 0.02), balance (z-score change, -1.0; 95% CI, -1.9 to -0.09; p = 0.03), and long jump (z-score change, -0.4; 95% CI, -0.7 to -0.02; p = 0.04). Of the most common genetic subtypes, 111 participants with CMT1A/PMP22 duplication progressed by 1.8 ± 4.2 (12% change from baseline; p < 0.001), 9 participants with CMT1B/MPZ mutation progressed by 2.2 ± 5.1 (11% change), 6 participants with CMT2A/MFN2 mutation progressed by 6.2 ± 7.9 (23% change), and 7 participants with CMT4C/SH3TC2 mutations progressed by 3.0 ± 4.5 (12% change). Participants with CMT2A progressed faster than CMT1A (mean difference, -4.4; 95% CI, -8.1 to -0.8; p = 0.02). Children with CMT1A progressed consistently through early childhood (3-10 years) and adolescence (11-20 years; mean difference, 1.1; 95% CI, -0.6 to 2.7; p = 0.19), whereas CMT2A appeared to progress faster during early childhood than adolescence (mean difference, 10.0; 95% CI, -2.2 to 22.2; p = 0.08). INTERPRETATION: Using the CMTPedS as an outcome measure of disease severity, children with CMT progress at a significant rate over 2 years. Understanding the rate at which children with CMT deteriorate is essential for adequately powering trials of disease-modifying interventions. Ann Neurol 2017;82:353-359.

Safety and efficacy of progressive resistance exercise for Charcot-Marie-Tooth disease in children: a randomised, double-blind, sham-controlled trial.

BACKGROUND: Exercise is potentially therapeutic for neuromuscular disorders, but a risk of harm exists due to overwork weakness. We aimed to assess the safety and efficacy of progressive resistance exercise for foot dorsiflexion weakness in children with Charcot-Marie-Tooth disease. METHODS: We did this randomised, double-blind, sham-controlled trial across the Sydney Children's Hospitals Network (NSW, Australia). Children aged 6-17 years with Charcot-Marie-Tooth disease were eligible if they had foot dorsiflexion weakness (negative Z score based on age-matched and sex-matched normative reference values). We randomly allocated (1:1) children, with random block sizes of 4, 6, and 8 and stratification by age, to receive 6 months (three times per week on non-consecutive days; 72 sessions in total) of progressive resistance training (from 50% to 70% of the most recent one repetition maximum) or sham training (negligible non-progressed intensity), using an adjustable exercise cuff to exercise the dorsiflexors of each foot. The primary efficacy outcome was the between-group difference in dorsiflexion strength assessed by hand-held dynamometry (expressed as a Z score) from baseline to months 6, 12, and 24. The primary safety outcome was the between-group difference in muscle and intramuscular fat volume of the anterior compartment of the lower leg assessed by MRI (expressed as a scaled volume) from baseline to 6 months and 24 months. Participants, parents, outcome evaluators, and investigators other than the treatment team were masked to treatment assignment. Analysis was by intention to treat. The trial is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12613000552785. FINDINGS: From Sept 2, 2013, to Dec 11, 2014, we randomly assigned 60 children to receive progressive resistance exercise (n=30) or sham training (n=30), and 55 (92%) children completed the trial. ANCOVA-adjusted Z score differences in dorsiflexion strength between groups were 0 (95% CI -0·37 to 0·42; p=0·91) at 6 months, 0·3 (-0·23 to 0·81; p=0·27) at 12 months, and 0·6 (95% CI 0·03 to 1·12; p=0·041) at 24 months. Scaled muscle and fat volume was comparable between groups at 6 months (ANCOVA-adjusted muscle volume difference 0, 95% CI -0·03 to 0·10, p=0·24; and fat volume difference 0, 95% CI -0·01 to 0·05, p=0·25) and 24 months (0, -0·08 to 0·12, p=0·67; and 0, -0·05 to 0·03, p=0·58). No serious adverse events were reported. INTERPRETATION: 6 months of targeted progressive resistance exercise attenuated long-term progression of dorsiflexion weakness without detrimental effect on muscle morphology or other signs of overwork weakness in paediatric patients with Charcot-Marie-Tooth disease. FUNDING: Muscular Dystrophy Association and Australian National Health and Medical Research Council.

Phenotypic Variability of Childhood Charcot-Marie-Tooth Disease.

IMPORTANCE: Disease severity of childhood Charcot-Marie-Tooth disease (CMT) has not been extensively characterized, either within or between types of CMT to date. OBJECTIVE: To assess the variability of disease severity in a large cohort of children and adolescents with CMT. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional study was conducted among 520 children and adolescents aged 3 to 20 years at 8 universities and hospitals involved in the Inherited Neuropathies Consortium between August 6, 2009, and July 31, 2014, in Australia, Italy, the United Kingdom, and the United States. Data analysis was conducted from August 1, 2014, to December 1, 2015. MAIN OUTCOMES AND MEASURES: Scores on the Charcot-Marie-Tooth Disease Pediatric Scale (CMTPedS), a well-validated unidimensional clinical outcome measure to assess disease severity. This instrument includes 11 items assessing fine and gross motor function, sensation, and balance to produce a total score ranging from 0 (unaffected) to 44 (severely affected). RESULTS: Among the 520 participants (274 males) aged 3 to 20 years, CMT type 1A (CMT1A) was the most prevalent type (252 [48.5%]), followed by CMT2A (31 [6.0%]), CMT1B (15 [2.9%]), CMT4C (13 [2.5%]), and CMTX1 (10 [1.9%]). Disease severity ranged from 1 to 44 points on the CMTPedS (mean [SD], 21.5 [8.9]), with ankle dorsiflexion strength and functional hand dexterity test being most affected. Participants with CMT1B (mean [SD] CMTPedS score, 24.0 [7.4]), CMT2A (29.7 [7.1]), and CMT4C (29.8 [8.6]) were more severely affected than those with CMT1A (18.9 [7.7]) and CMTX1 (males: 15.3 [7.7]; females: 13.0 [3.6]) (P < .05). Scores on the CMTPedS tended to worsen principally during childhood (ages, 3-10 years) for participants with CMT4C and CMTX1 and predominantly during adolescence for those with CMT1B and CMT2A (ages, 11-20 years), while CMT1A worsened consistently throughout childhood and adolescence. For individual items, participants with CMT4C recorded more affected functional dexterity test scores than did those with all other types of CMT (P < .05). Participants with CMT1A and CMTX1 performed significantly better on the 9-hole peg test and balance test than did those with all other types of CMT (P < .05). Participants with CMT2A had the weakest grip strength (P < .05), while those with CMT2A and CMT4C exhibited the weakest ankle plantarflexion and dorsiflexion strength, as well as the lowest long jump and 6-minute walk test distances (P < .05). Multiple regression modeling identified increasing age (r = 0.356, ß = 0.617, P < .001) height (r = 0.251, ß = 0.309, P = .002), self-reported foot pain (r = 0.162, ß = .114, P = .009), and self-reported hand weakness (r = 0.243, ß = 0.203, P < .001) as independent predictors of disease severity. CONCLUSIONS AND RELEVANCE: These results highlight the phenotypic variability within CMT genotypes and mutation-specific manifestations between types. This study has identified distinct functional limitations and self-reported impairments to target in future therapeutic trials.

Muscle weakness in children with neurofibromatosis type 1.

AIM: To investigate if children with neurofibromatosis type 1 (NF1) have reduced muscle strength compared with children with typical development. METHOD: Maximal isometric strength of 15 upper and lower limb muscle groups was evaluated in 30 children with NF1 (16 males, 14 females; aged 4-16y) and 30 age-, sex-, height-, and weight-matched controls using hand-held dynamometry by a single evaluator. Both the left and right sides were assessed. RESULTS: Children with NF1 were significantly weaker than children with typical development across all 15 muscle groups assessed (p<0.05). Apart from elbow flexion, there were no differences between the left and right sides (p>0.05). Magnitude of differences between the children with NF1 compared with the controls ranged from 3% to 43%. Males and females were equally affected. INTERPRETATION: This study shows that children with NF1 have reduced muscle strength compared with children with typical development. This muscle weakness is present from the earliest stages of the disease assessed and persists throughout childhood with no sex difference. These results support recent evidence from mouse studies that NF1 is associated with a primary myopathy.