The 6-minute walk test and other clinical endpoints in duchenne muscular dystrophy: reliability, concurrent validity, and minimal clinically important differences from a multicenter study

Validation of 6 min step test and 4-m gait speed in children: A randomized cross-over study

INTRODUCTION

Even if 6-min walking test (6MWT) is the criterion standard for functional exercise performance evaluation, new field tests are required as practical alternative. This study aims to establish the validity of the 6-min step test (6MST) and the 4-m gait speed (4MGS) in children.

METHOD

It is a randomized cross-over trial. Sixty one healthy children from 6 to 12 years were recruited. 6MWT, 6MST and 4MGS were randomly performed on three consecutive days. Pulsed oxygen saturation (SpO2), heart rate (HR), dyspnea (VAS) and fatigue (PCERT) were used as outcomes.

RESULTS

The distance walked during 6MWT was correlated to the number of steps during 6MST (r = 0.320; p = 0.013) and not correlated to 4MGS (r = -0.074; p = 0.575). No correlation between number of steps during 6MST and 4MGS (r = -0.129; p = 0.332) was found. HR was lower than the theoretical maximal HR after the tests. The increase in HR was significantly higher for 6MST and significantly lower for 4MGS than for 6MWT and it was higher for 6MST than for 4MGS. Dyspnea and perceived exertion were lower after 6MWT than after 6MST and higher than after 4MGS. They were also higher during 6MST than during 4MGS.

CONCLUSION

The three field tests are feasible in children. The 6MST and 4MGS are not valid surrogates to 6MWT in healthy children for functional exercise performance evaluation. Moreover, the cardio-respiratory response differs between the three tests.

Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and neuromuscular, rehabilitation, endocrine, and gastrointestinal and nutritional management

Since the publication of the Duchenne muscular dystrophy (DMD) care considerations in 2010, multidisciplinary care of this severe, progressive neuromuscular disease has evolved. In conjunction with improved patient survival, a shift to more anticipatory diagnostic and therapeutic strategies has occurred, with a renewed focus on patient quality of life. In 2014, a steering committee of experts from a wide range of disciplines was established to update the 2010 DMD care considerations, with the goal of improving patient care. The new care considerations aim to address the needs of patients with prolonged survival, to provide guidance on advances in assessments and interventions, and to consider the implications of emerging genetic and molecular therapies for DMD. The committee identified 11 topics to be included in the update, eight of which were addressed in the original care considerations. The three new topics are primary care and emergency management, endocrine management, and transitions of care across the lifespan. In part 1 of this three-part update, we present care considerations for diagnosis of DMD and neuromuscular, rehabilitation, endocrine (growth, puberty, and adrenal insufficiency), and gastrointestinal (including nutrition and dysphagia) management.

Evaluation of serum MMP-9 as predictive biomarker for antisense therapy in Duchenne

Duchenne Muscular Dystrophy (DMD) is a severe muscle disorder caused by lack of dystrophin. Predictive biomarkers able to anticipate response to the therapeutic treatments aiming at dystrophin re-expression are lacking. The objective of this study is to investigate Matrix Metalloproteinase-9 (MMP-9) as predictive biomarker for Duchenne. Two natural history cohorts were studied including 168 longitudinal samples belonging to 66 patients. We further studied 1536 samples obtained from 3 independent clinical trials with drisapersen, an antisense oligonucleotide targeting exon 51: an open label study including 12 patients; a phase 3 randomized, double blind, placebo controlled study involving 186 patients; an open label extension study performed after the phase 3. Analysis of natural history cohorts showed elevated MMP-9 levels in patients and a significant increase over time in longitudinal samples. MMP-9 decreased in parallel to clinical stabilization in the 12 patients involved in the open label study. The phase 3 study and subsequent extension study clarified that the decrease in MMP-9 levels was not predictive of treatment response. These data do not support the inclusion of serum MMP-9 as predictive biomarker for DMD patients.

A randomized placebo-controlled phase 3 trial of an antisense oligonucleotide, drisapersen, in Duchenne muscular dystrophy

This 48-week, randomized, placebo-controlled phase 3 study (DMD114044; NCT01254019) evaluated efficacy and safety of subcutaneous drisapersen 6 mg/kg/week in 186 ambulant boys aged ≥5 years, with Duchenne muscular dystrophy (DMD) resulting from an exon 51 skipping amenable mutation. Drisapersen was generally well tolerated, with injection-site reactions and renal events as most commonly reported adverse events. A nonsignificant treatment difference (P = 0.415) in the change from baseline in six-minute walk distance (6MWD; primary efficacy endpoint) of 10.3 meters in favor of drisapersen was observed at week 48. Key secondary efficacy endpoints (North Star Ambulatory Assessment, 4-stair climb ascent velocity, and 10-meter walk/run velocity) gave consistent findings. Lack of statistical significance was thought to be largely due to greater data variability and subgroup heterogeneity. The increased standard deviation alone, due to less stringent inclusion/exclusion criteria, reduced the statistical power from pre-specified 90% to actual 53%. Therefore, a post-hoc analysis was performed in 80 subjects with a baseline 6MWD 300-400 meters and ability to rise from floor. A statistically significant improvement in 6MWD of 35.4 meters (P = 0.039) in favor of drisapersen was observed in this subpopulation. Results suggest that drisapersen could have benefit in a less impaired population of DMD subjects.

Timed function tests, motor function measure, and quantitative thigh muscle MRI in ambulant children with Duchenne muscular dystrophy: A cross-sectional analysis

The development of new therapeutic agents for the treatment of Duchenne muscular dystrophy has put a focus on defining outcome measures most sensitive to capture treatment effects. This cross-sectional analysis investigates the relation between validated clinical assessments such as the 6-minute walk test, motor function measure and quantitative muscle MRI of thigh muscles in ambulant Duchenne muscular dystrophy patients, aged 6.5 to 10.8 years (mean 8.2, SD 1.1). Quantitative muscle MRI included the mean fat fraction using a 2-point Dixon technique, and transverse relaxation time (T2) measurements. All clinical assessments were highly significantly inter-correlated with p < 0.001. The strongest correlation with the motor function measure and its D1-subscore was shown by the 6-minute walk test. Clinical assessments showed no correlation with age. Importantly, quantitative muscle MRI values significantly correlated with all clinical assessments with the extensors showing the strongest correlation. In contrast to the clinical assessments, quantitative muscle MRI values were highly significantly correlated with age. In conclusion, the motor function measure and timed function tests measure disease severity in a highly comparable fashion and all tests correlated with quantitative muscle MRI values quantifying fatty muscle degeneration.

Duchenne and Becker Muscular Dystrophies: A Review of Animal Models, Clinical End Points, and Biomarker Quantification

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are neuromuscular disorders that primarily affect boys due to an X-linked mutation in the DMD gene, resulting in reduced to near absence of dystrophin or expression of truncated forms of dystrophin. Some newer therapeutic interventions aim to increase sarcolemmal dystrophin expression, and accurate dystrophin quantification is critical for demonstrating pharmacodynamic relationships in preclinical studies and clinical trials. Current challenges with measuring dystrophin include the variation in protein expression within individual muscle fibers and across whole muscle samples, the presence of preexisting dystrophin-positive revertant fibers, and trace amounts of residual dystrophin. Immunofluorescence quantification of dystrophin can overcome many of these challenges, but manual quantification of protein expression may be complicated by variations in the collection of images, reproducible scoring of fluorescent intensity, and bias introduced by manual scoring of typically only a few high-power fields. This review highlights the pathology of DMD and BMD, discusses animal models of DMD and BMD, and describes dystrophin biomarker quantitation in DMD and BMD, with several image analysis approaches, including a new automated method that evaluates protein expression of individual muscle fibers.

Ataluren in patients with nonsense mutation Duchenne muscular dystrophy (ACT DMD): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

Duchenne muscular dystrophy (DMD) is a severe, progressive, and rare neuromuscular, X-linked recessive disease. Dystrophin deficiency is the underlying cause of disease; therefore, mutation-specific therapies aimed at restoring dystrophin protein production are being explored. We aimed to assess the efficacy and safety of ataluren in ambulatory boys with nonsense mutation DMD.

METHODS

We did this multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 54 sites in 18 countries located in North America, Europe, the Asia-Pacific region, and Latin America. Boys aged 7-16 years with nonsense mutation DMD and a baseline 6-minute walk distance (6MWD) of 150 m or more and 80% or less of the predicted normal value for age and height were randomly assigned (1:1), via permuted block randomisation (block size of four) using an interactive voice-response or web-response system, to receive ataluren orally three times daily (40 mg/kg per day) or matching placebo. Randomisation was stratified by age (<9 years vs ≥9 years), duration of previous corticosteroid use (6 months to <12 months vs ≥12 months), and baseline 6MWD (<350 m vs ≥350 m). Patients, parents and caregivers, investigational site personnel, PTC Therapeutics employees, and all other study personnel were masked to group allocation until after database lock. The primary endpoint was change in 6MWD from baseline to week 48. We additionally did a prespecified subgroup analysis of the primary endpoint, based on baseline 6MWD, which is reflective of anticipated rates of disease progression over 1 year. The primary analysis was by intention to treat. This study is registered with ClinicalTrials.gov, number NCT01826487.

FINDINGS

Between March 26, 2013, and Aug 26, 2014, we randomly assigned 230 patients to receive ataluren (n=115) or placebo (n=115); 228 patients comprised the intention-to-treat population. The least-squares mean change in 6MWD from baseline to week 48 was -47·7 m (SE 9·3) for ataluren-treated patients and -60·7 m (9·3) for placebo-treated patients (difference 13·0 m [SE 10·4], 95% CI -7·4 to 33·4; p=0·213). The least-squares mean change for ataluren versus placebo in the prespecified subgroups was -7·7 m (SE 24·1, 95% CI -54·9 to 39·5; p=0·749) in the group with a 6MWD of less than 300 m, 42·9 m (15·9, 11·8-74·0; p=0·007) in the group with a 6MWD of 300 m or more to less than 400 m, and -9·5 m (17·2, -43·2 to 24·2; p=0·580) in the group with a 6MWD of 400 m or more. Ataluren was generally well tolerated and most treatment-emergent adverse events were mild to moderate in severity. Eight (3%) patients (n=4 per group) reported serious adverse events; all except one event in the placebo group (abnormal hepatic function deemed possibly related to treatment) were deemed unrelated to treatment.

INTERPRETATION

Change in 6MWD did not differ significantly between patients in the ataluren group and those in the placebo group, neither in the intention-to-treat population nor in the prespecified subgroups with a baseline 6MWD of less than 300 m or 400 m or more. However, we recorded a significant effect of ataluren in the prespecified subgroup of patients with a baseline 6MWD of 300 m or more to less than 400 m. Baseline 6MWD values within this range were associated with a more predictable rate of decline over 1 year; this finding has implications for the design of future DMD trials with the 6-minute walk test as the endpoint.

FUNDING

PTC Therapeutics.

Developing a Natural History Progression Model for Duchenne Muscular Dystrophy Using the Six-Minute Walk Test

The 6-minute walk test (6MWT) is used as a clinical endpoint to evaluate drug efficacy in Duchenne Muscular Dystrophy (DMD) trials. A model was developed using digitized 6MWT data that estimated two slopes and two intercepts to characterize 6MWT improvement during development and 6MWT decline. Mean baseline 6MWT was 362 (±87) meters. The model predicted an improvement at a rate of 20 meters/year (95% confidence interval (CI) = 9.4-30) up until 10 years old (95% CI = 6.78-13.1), and then a decline at a rate of 85 meters/year (95% CI = 72-98). Interpatient slope variability for improvement and decline were similar at 21.9 percentage of coefficient of variation (%CV) and 23.3%CV, respectively. Model simulations using age demographics from a previous DMD natural history study could reasonably predict the trend in improvement and decline in the 6MWT. This model can be used to quantitate individual patient trajectories, identify prognostic factors for disease progression, and evaluate drug effect.

Monitoring guidance for patients with hypophosphatasia treated with asfotase alfa

Hypophosphatasia (HPP) is a rare, inherited, systemic, metabolic disorder caused by autosomal recessive mutations or a single dominant-negative mutation in the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). The disease is associated with a broad range of signs, symptoms, and complications, including impaired skeletal mineralization, altered calcium and phosphate metabolism, recurrent fractures, pain, respiratory problems, impaired growth and mobility, premature tooth loss, developmental delay, and seizures. Asfotase alfa is a human, recombinant enzyme replacement therapy that is approved in many countries for the treatment of patients with HPP. To address the unmet need for guidance in the monitoring of patients receiving asfotase alfa, an international panel of physicians with experience in diagnosing and managing HPP convened in May 2016 to discuss treatment monitoring parameters. The panel discussions focused on recommendations for assessing and monitoring patients after the decision to treat with asfotase alfa had been made and did not include recommendations for whom to treat. Based on the consensus of panel members, this review provides guidance on the monitoring of patients with HPP during treatment with asfotase alfa, including recommendations for laboratory, efficacy, and safety assessments and the frequency with which these should be performed during the course of treatment. Recommended assessments are based on patient age and include regular monitoring of biochemistry, skeletal radiographs, respiratory function, growth, pain, mobility and motor function, and quality of life. Because of the systemic presentation of HPP, a coordinated, multidisciplinary, team-based, patient-focused approach is recommended in the management of patients receiving asfotase alfa. Monitoring of efficacy and safety outcomes must be tailored to the individual patient, depending on medical history, clinical manifestations, availability of resources in the clinical setting, and the clinician's professional judgment.

Characterization of Strength and Function in Ambulatory Adults With GNE Myopathy

Objective:

To characterize the pattern and extent of muscle weakness and impact on physical functioning in adults with GNEM.

Methods:

Strength and function were assessed in GNEM subjects (n = 47) using hand-held dynamometry, manual muscle testing, upper and lower extremity functional capacity tests, and the GNEM-Functional Activity Scale (GNEM-FAS).

Results:

Profound upper and lower muscle weakness was measured using hand-held dynamometry in a characteristic pattern, previously described. Functional tests and clinician-reported outcomes demonstrated the consequence of muscle weakness on physical functioning.

Conclusions:

The characteristic pattern of upper and lower muscle weakness associated with GNEM and the resulting functional limitations can be reliably measured using these clinical outcome assessments of muscle strength and function.

Differences in Adipose Tissue and Lean Mass Distribution in Patients with Collagen VI Related Myopathies Are Associated with Disease Severity and Physical Ability

Mutations in human collagen VI genes cause a spectrum of musculoskeletal conditions in children and adults collectively termed collagen VI-related myopathies (COL6-RM) characterized by a varying degree of muscle weakness and joint contractures and which include Ullrich Congenital Muscular Dystrophy (UCMD) and Bethlem Myopathy (BM). Given that collagen VI is one of the most abundant extracellular matrix proteins in adipose tissue and its emerging role in energy metabolism we hypothesized that collagen VI deficiency might be associated with alterations in adipose tissue distribution and adipokines serum profile. We analyzed body composition by means of dual-energy X-ray absorptiometry in 30 pediatric and adult COL6-RM myopathy patients representing a range of severities (UCMD, intermediate-COL6-RM, and BM). We found a distinctive pattern of regional adipose tissue accumulation which was more evident in children at the most severe end of the spectrum. In particular, the accumulation of fat in the android region was a distinguishing feature of UCMD patients. In parallel, there was a decrease in lean mass compatible with a state of sarcopenia, particularly in ambulant children with an intermediate phenotype. All children and adult patients that were sarcopenic were also obese. These changes were significantly more pronounced in children with collagen VI deficiency than in children with Duchenne Muscular Dystrophy of the same ambulatory status. High molecular weight adiponectin and leptin were significantly increased in sera from children in the intermediate and BM group. Correlation analysis showed that the parameters of fat mass were negatively associated with motor function according to several validated outcome measures. In contrast, lean mass parameters correlated positively with physical performance and quality of life. Leptin and adiponectin circulating levels correlated positively with fat mass parameters and negatively with lean mass and thus may be relevant to the disease pathogenesis and as circulating markers. Taken together our results indicate that COL6-RM are characterized by specific changes in total fat mass and distribution which associate with disease severity, motor function, and quality of life and which are clinically meaningful and thus should be taken into consideration in the management of these patients.

Associations between treatment, scoliosis, pulmonary function, and physical performance in long-term survivors of sarcoma

PURPOSE

Longer survival for children with sarcoma has led to the recognition of chronic health conditions related to prior therapy. We sought to study the association of sarcoma therapy with the development of scoliosis.

METHODS

We reviewed patient demographics, treatment exposures, and functional outcomes for patients surviving >10 years after treatment for sarcoma between 1964 and 2002 at our institution. The diagnosis of scoliosis was determined by imaging. Functional performance and standardized questionnaires were completed in a long-term follow-up clinic.

RESULTS

We identified 367 patients, with median age at follow-up of 33.1 years. Scoliosis was identified in 100 (27.2%) patients. Chest radiation (relative risk (RR), 1.88 (95% confidence interval (CI), 1.21-2.92), p < 0.005) and rib resection (RR, 2.64 (CI, 1.79-3.89), p < 0.0001) were associated with an increased incidence of scoliosis; thoracotomy without rib resection was not. Of 21 patients who underwent rib resection, 16 (80.8%) had the apex of scoliosis towards the surgical side. Scoliosis was associated with worse pulmonary function (RR, 1.74 (CI, 1.14-2.66), p < 0.01) and self-reported health outcomes, including functional impairment (RR, 1.60 (CI, 1.07-2.38), p < 0.05) and cancer-related pain (RR, 1.55 (CI, 1.11-2.16), p < 0.01). Interestingly, pulmonary function was not associated with performance on the 6-min walk test in this young population.

CONCLUSIONS

Children with sarcoma are at risk of developing scoliosis when treatment regimens include chest radiation or rib resection. Identification of these risk factors may allow for early intervention designed to prevent adverse long-term outcomes.

IMPLICATIONS FOR CANCER SURVIVORS

Cancer survivors at risk of developing scoliosis may benefit from monitoring of pulmonary status and early physical therapy.

Electrical impedance myography for assessment of Duchenne muscular dystrophy

OBJECTIVE

Sensitive, objective, and easily applied methods for evaluating disease progression and response to therapy are needed for clinical trials in Duchenne muscular dystrophy (DMD). In this study, we evaluated whether electrical impedance myography (EIM) could serve this purpose.

METHODS

In this nonblinded study, 36 boys with DMD and 29 age-similar healthy boys underwent multifrequency EIM measurements for up to 2 years on 6 muscles unilaterally along with functional assessments. A linear mixed-effects model with random intercept and slope terms was used for the analysis of multifrequency EIM values and functional measures. Seven DMD boys were initiated on corticosteroids; these data were analyzed using a piecewise linear mixed-effects model.

RESULTS

In boys > 7.0 years old, a significant difference in the slope of EIM phase ratio trajectories in the upper extremity was observed by 6 months of -0.074/month, p = 0.023, 95% confidence interval (CI) = -0.013, -0.14; at 2 years, this difference was -0.048/month, p < 0.0001, 95% CI = -0.028, -0.068. In boys ≤ 7.0 years old, differences appeared at 6 months in gastrocnemius (EIM phase slope = -0.83 °/kHz/mo, p = 0.007, 95% CI = -0.26, -1.40). EIM outcomes showed significant differences earlier than functional tests. Initiation of corticosteroids significantly improved the slope of EIM phase ratio (0.057/mo, p = 0.00019, 95% CI = 0.028, 0.086) and EIM phase slope (0.14 °/kHz/mo, p = 0.013, 95% CI = 0.028, 0.25), consistent with corticosteroids' known clinical benefit.

INTERPRETATION

EIM detects deterioration in muscles of both younger and older boys by 6 months; it also identifies the therapeutic effect of corticosteroid initiation. Because EIM is rapid to apply, painless, and requires minimal operator training, the technique deserves to be further evaluated as a biomarker in DMD clinical therapeutic trials. Ann Neurol 2017;81:622-632.

Minimal clinically important difference for the 6-min walk test: literature review and application to Morquio A syndrome

Morquio A syndrome is an ultra-rare, inherited lysosomal storage disorder associated with progressive, multi-systemic clinical impairments, causing gradual loss of functional capacity and endurance, impaired quality of life, and early mortality. Studies in Morquio A patients have used the 6-min walk test (6MWT) to assess functionality and endurance and to evaluate disease progression or efficacy of treatment. The objective of the present study was to review minimal clinically important differences (MCIDs) for the 6MWT reported for disease states that widely use the 6MWT to evaluate clinical benefit and to discuss the results in view of the challenges in estimating MCID for ultra-rare diseases, using the case of elosulfase alfa in Morquio A patients. A systematic literature search was performed using Embase and Medline to identify studies specifically estimating the MCID using either anchor-based or distribution-based methods. A total of 19 publications on 17 studies were identified; none of these included patients with Morquio A syndrome or the wider disease category of lysosomal storage disorders. Therefore, the MCIDs determined by studies in patients with respiratory, cardiovascular, or musculoskeletal disease were compared to changes in the 6MWT seen in Morquio A patients in the pivotal phase 3 clinical trial of elosulfase alfa enzyme replacement therapy. The literature review showed a mean MCID for the 6MWT of 7% change (range 3–15%) in studies using anchor-based methods and a 9% change (range 4–16%) using distribution-based methods. Results of the elosulfase alfa clinical trial and its extension showed a placebo-adjusted 14.9% improvement in the 6MWT from baseline at week 24, which was greater than the mean MCID based on the results of the systematic literature review. After 2 years, 6MWT distance increased by a mean of 20.7% from baseline in a modified per-protocol population, versus a reduction of 6.9% in comparable untreated patients from the MorCAP natural history study over the same period. Although further research is required to establish the MCID of the 6MWT in Morquio A patients, the presented data provide further evidence for the positive effect of elosulfase alfa in this patient population.

Exercise in myasthenia gravis: A feasibility study of aerobic and resistance training

INTRODUCTION

It has not been established whether progressive resistance training (PRT) and aerobic training (AT) are feasible and efficient in myasthenia gravis (MG).

METHODS

Fifteen subjects with generalized MG (Myasthenia Gravis Foundation of America (MGFA) clinical classification II-IV) were randomly assigned to 20 training sessions during 8 weeks of either PRT or AT. Feasibility was evaluated based on adherence, drop-out rate, adverse events, and Quantitative Myasthenia Gravis (QMG) score.

RESULTS

Twelve subjects (MGFA II, n = 11; MGFA III, n=1) completed the intervention with a mean adherence of 95 % ± 8. One dropout (PRT) could potentially be related to PRT. Both groups reported adverse events, including bulbar symptoms (n = 2) and increased fatigue (n = 3), but no change in QMG score was observed in either group. The PRT group showed increases in maximal strength and functional capacity.

CONCLUSIONS

Eight weeks of moderate to high intensity AT and PRT were feasible for most patients with mild MG. Maximal strength and functional capacity increased in the PRT group. Muscle Nerve 56: 700-709, 2017.

Patient-Centered Therapy Development for Myotonic Dystrophy: Report of the Myotonic Dystrophy Foundation-Sponsored Workshop

Myotonic dystrophy (DM) is an autosomal dominant, repeat expansion, progressive disorder with no drug therapies. Consequently, to better define a regulatory pathway in anticipation of new treatment strategies under investigation, the Myotonic Dystrophy Foundation convened a workshop entitled "Patient-Centered Therapy Development for Myotonic Dystrophy" in September 2015. Participants included representatives from academia, industry, the patient community, the National Institutes of Health (NIH) and the Food and Drug Administration (FDA). Presenters described the symptom burden of the disease, and existing data on DM biomarkers, endpoints, natural history, and benefit-risk considerations. FDA participants helped clarify the regulatory requirements for new drug treatment approvals and DM-specific issues such as variability, slow progression, and low prevalence. Workshop attendees gained a better understanding of DM and the current status of existing data and tools to support therapeutic drug research and development.

Feasibility and tolerability of whole-body, low-intensity vibration and its effects on muscle function and bone in patients with dystrophinopathies: a pilot study

Introduction

Dystrophinopathies are X‐linked muscle degenerative disorders that result in progressive muscle weakness complicated by bone loss. This study's goal was to evaluate feasibility and tolerability of whole‐body, low‐intensity vibration (WBLIV) and its potential effects on muscle and bone in patients with Duchenne or Becker muscular dystrophy.

Methods

This 12‐month pilot study included 5 patients (age 5.9–21.7 years) who used a low‐intensity Marodyne LivMD plate vibrating at 30–90 Hz for 10 min/day for the first 6 months. Timed motor function tests, myometry, and peripheral quantitative computed tomography were performed at baseline and at 6 and 12 months.

Results

Motor function and lower extremity muscle strength remained either unchanged or improved during the intervention phase, followed by deterioration after WBLIV discontinuation. Indices of bone density and geometry remained stable in the tibia.

Conclusions

WBLIV was well tolerated and appeared to have a stabilizing effect on lower extremity muscle function and bone measures. Muscle Nerve55: 875–883, 2017

Nonsense Suppression as an Approach to Treat Lysosomal Storage Diseases

In-frame premature termination codons (PTCs) (also referred to as nonsense mutations) comprise ~10% of all disease-associated gene lesions. PTCs reduce gene expression in two ways. First, PTCs prematurely terminate translation of an mRNA, leading to the production of a truncated polypeptide that often lacks normal function and/or is unstable. Second, PTCs trigger degradation of an mRNA by activating nonsense-mediated mRNA decay (NMD), a cellular pathway that recognizes and degrades mRNAs containing a PTC. Thus, translation termination and NMD are putative therapeutic targets for the development of treatments for genetic diseases caused by PTCs. Over the past decade, significant progress has been made in the identification of compounds with the ability to suppress translation termination of PTCs (also referred to as readthrough). More recently, NMD inhibitors have also been explored as a way to enhance the efficiency of PTC suppression. Due to their relatively low threshold for correction, lysosomal storage diseases are a particularly relevant group of diseases to investigate the feasibility of nonsense suppression as a therapeutic approach. In this review, the current status of PTC suppression and NMD inhibition as potential treatments for lysosomal storage diseases will be discussed.

Comparison of ambulatory capacity and disease progression of Duchenne muscular dystrophy subjects enrolled in the drisapersen DMD114673 study with a matched natural history cohort of subjects on daily corticosteroids

Duchenne muscular dystrophy is a rare genetic disorder with life-limiting pathology. Drisapersen induces exon 51 skipping, thereby producing a shorter but functional dystrophin protein. The longest available data are from an open-label extension study (PRO051-02) treating 12 boys with drisapersen (6 mg/kg/week subcutaneously). The median change (range) from baseline to week 177 in six-minute walking distance (6MWD) was 8 (-263, 163) metres. The current analysis aimed to put the results from PRO051-02 in the context of natural progression by comparing the functional trajectory of drisapersen-treated subjects to a matched natural history (NH) cohort, treated by standard of care. Subjects were matched individually by age and 6MWD, as the primary analysis, and by age and rise from floor (RFF), as sensitivity analysis. A total of 75 NH subjects were available for 6MWD analysis, of which matching was possible for 9 ambulant drisapersen-treated subjects. None of the 6 "stable" (baseline 6MWD ≥330 metres) drisapersen-treated subjects lost ambulation vs 4 out of 10 matched NH subjects over a comparable timeframe (~3.4 years), compared with 2 out of 3 ambulant "in decline" drisapersen-treated subjects vs all 6 matched NH subjects. A total of 79 NH subjects were available for RFF analysis. For continuous ambulatory subjects (N = 4), the RFF decline was more pronounced in the NH cohort than in the drisapersen-treated subjects. In conclusion, a comparison of ambulant drisapersen-treated subjects with matched NH subjects showed a difference in functional trajectories over a timeframe of up to 3.4 years in favour of drisapersen.

Analysis of Gait Disturbance in Glut 1 Deficiency Syndrome

Anticipating potential therapies for Glut 1 deficiency syndrome (Glut1DS) emphasizes the need for effective clinical outcome measures. The 6-minute walk test is a well-established outcome measure that evaluates walking ability in neurological diseases. Twenty-one children with Glut 1 deficiency syndrome and 21 controls performed the 6-minute walk test. Fatigue was determined by comparing distance walked in the first and sixth minutes. Gait was analyzed by stride length, velocity, cadence, base of support, and percentage time in double support. Independent sample t-tests examined differences between group. Repeated-measures analysis of variance evaluated gait parameters over time. Glut 1 deficiency syndrome patients walked less (P < .05), had slower velocities (P < .0001), had shorter stride lengths (P < .0001), spent more time in double support (P < .001), and had increasing variability in base of support (P = .009). Glut 1 deficiency syndrome patients have impaired motor performance, walk more slowly, and have poor balance. The 6-minute walk test with gait analysis may serve as a useful outcome measure in clinical trials in Glut 1 deficiency syndrome.

Using Touch-evoked Response and Locomotion Assays to Assess Muscle Performance and Function in Zebrafish

Zebrafish muscle development is highly conserved with mammalian systems making them an excellent model to study muscle function and disease. Many myopathies affecting skeletal muscle function can be quickly and easily assessed in zebrafish over the first few days of embryogenesis. By 24 hr post-fertilization (hpf), wildtype zebrafish spontaneously contract their tail muscles and by 48 hpf, zebrafish exhibit controlled swimming behaviors. Reduction in the frequency of, or other alterations in, these movements may indicate a skeletal muscle dysfunction. To analyze swimming behavior and assess muscle performance in early zebrafish development, we utilize both touch-evoked escape response and locomotion assays.

Touch-evoked escape response assays can be used to assess muscle performance during short burst movements resulting from contraction of fast-twitch muscle fibers. In response to an external stimulus, which in this case is a tap on the head, wildtype zebrafish at 2 days post-fertilization (dpf) typically exhibit a powerful burst swim, accompanied by sharp turns. Our method quantifies skeletal muscle function by measuring the maximum acceleration during a burst swimming motion, the acceleration being directly proportional to the force produced by muscle contraction.

In contrast, locomotion assays during early zebrafish larval development are used to assess muscle performance during sustained periods of muscle activity. Using a tracking system to monitor swimming behavior, we obtain an automated calculation of the frequency of activity and distance in 6-day old zebrafish, reflective of their skeletal muscle function. Measurements of swimming performance are valuable for phenotypic assessment of disease models and high-throughput screening of mutations or chemical treatments affecting skeletal muscle function.

Digital Droplet PCR for the Absolute Quantification of Exon Skipping Induced by Antisense Oligonucleotides in (Pre-)Clinical Development for Duchenne Muscular Dystrophy

Antisense oligonucleotides (AONs) in clinical development for Duchenne muscular dystrophy (DMD) aim to induce skipping of a specific exon of the dystrophin transcript during pre-mRNA splicing. This results in restoration of the open reading frame and consequently synthesis of a dystrophin protein with a shorter yet functional central rod domain. To monitor the molecular therapeutic effect of exon skip-inducing AONs in clinical studies, accurate quantification of pre- and post-treatment exon skip levels is required. With the recent introduction of 3^rd generation digital droplet PCR (ddPCR), a state-of-the-art technology became available which allows absolute quantification of transcript copy numbers with and without specific exon skip with high precision, sensitivity and reproducibility. Using Taqman assays with probes targeting specific exon-exon junctions, we here demonstrate that ddPCR reproducibly quantified cDNA fragments with and without exon 51 of the DMD gene over a 4-log dynamic range. In a comparison of conventional nested PCR, qPCR and ddPCR using cDNA constructs with and without exon 51 mixed in different molar ratios using, ddPCR quantification came closest to the expected outcome over the full range of ratios (0–100%), while qPCR and in particular nested PCR overestimated the relative percentage of the construct lacking exon 51. Highest accuracy was similarly obtained with ddPCR in DMD patient-derived muscle cells treated with an AON inducing exon 51 skipping. We therefore recommend implementation of ddPCR for quantification of exon skip efficiencies of AONs in (pre)clinical development for DMD.

A systematic review to investigate the measurement properties of goal attainment scaling, towards use in drug trials

Background

One of the main challenges for drug evaluation in rare diseases is the often heterogeneous course of these diseases. Traditional outcome measures may not be applicable for all patients, when they are in different stages of their disease. For instance, in Duchenne Muscular Dystrophy, the Six Minute Walk Test is often used to evaluate potential new treatments, whereas this outcome is irrelevant for patients who are already in a wheelchair. A measurement instrument such as Goal Attainment Scaling (GAS) can evaluate the effect of an intervention on an individual basis, and may be able to include patients even when they are in different stages of their disease. It allows patients to set individual goals, together with their treating professional. However, the validity of GAS as a measurement instrument in drug studies has never been systematically reviewed. Therefore, we have performed a systematic review to answer two questions: 1. Has GAS been used as a measurement instrument in drug studies? 2: What is known of the validity, responsiveness and inter- and intra-rater reliability of GAS, particularly in drug trials?

Methods

We set up a sensitive search that yielded 3818 abstracts. After careful screening, data-extraction was executed for 58 selected articles.

Results

Of the 58 selected articles, 38 articles described drug studies where GAS was used as an outcome measure, and 20 articles described measurement properties of GAS in other settings. The results show that validity, responsiveness and reliability of GAS in drug studies have hardly been investigated. The quality of the reporting of validity in studies in which GAS was used to evaluate a non-drug intervention also leaves much room for improvement.

Conclusions

We conclude that there is insufficient information to assess the validity of GAS, due to the poor quality of the validity studies. Therefore, we think that GAS needs further validation in drug studies, especially since GAS can be a potential solution when a small heterogeneous patient group is all there is to test a promising new drug.

Trial registration

The protocol has been registered in the PROSPERO international prospective register for systematic reviews, with registration number CRD42014010619. http://www.crd.york.ac.uk/PROSPERO/display_record.asp?ID=CRD42014010619.

Electronic supplementary material

The online version of this article (doi:10.1186/s12874-016-0205-4) contains supplementary material, which is available to authorized users.

Adaptive Immune Response Impairs the Efficacy of Autologous Transplantation of Engineered Stem Cells in Dystrophic Dogs

Duchenne muscular dystrophy is the most common genetic muscular dystrophy. It is caused by mutations in the dystrophin gene, leading to absence of muscular dystrophin and to progressive degeneration of skeletal muscle. We have demonstrated that the exon skipping method safely and efficiently brings to the expression of a functional dystrophin in dystrophic CD133+ cells injected scid/mdx mice. Golden Retriever muscular dystrophic (GRMD) dogs represent the best preclinical model of Duchenne muscular dystrophy, mimicking the human pathology in genotypic and phenotypic aspects. Here, we assess the capacity of intra-arterial delivered autologous engineered canine CD133+ cells of restoring dystrophin expression in Golden Retriever muscular dystrophy. This is the first demonstration of five-year follow up study, showing initial clinical amelioration followed by stabilization in mild and severe affected Golden Retriever muscular dystrophy dogs. The occurrence of T-cell response in three Golden Retriever muscular dystrophy dogs, consistent with a memory response boosted by the exon skipped-dystrophin protein, suggests an adaptive immune response against dystrophin.

Clinical potential of ataluren in the treatment of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an autosomal dominant, X-linked neuromuscular disorder caused by mutations in dystrophin, one of the largest genes known to date. Dystrophin gene mutations are generally transmitted from the mother to male offspring and can occur throughout the coding length of the gene. The majority of the methodologies aimed at treating the disorder have focused on restoring a shorter, although partially functional, dystrophin protein. The approach has the potential of converting a severe DMD phenotype into a milder form of the disease known as Becker muscular dystrophy. Others have focused on ameliorating the disease by targeting secondary pathologies such as inflammation or loss of regeneration. Of great potential is the development of strategies that are capable of restoring full-length dystrophin expression due to their ability to produce a normal, fully functional protein. Among these strategies, the use of read-through compounds (RTCs) that could be administered orally represents an ideal option. Gentamicin has been previously tested in clinical trials for DMD with limited or no success, and its use in the clinic has been dismissed due to issues of toxicity and lack of clear benefits to patients. More recently, new RTCs have been identified and tested in animal models for DMD. This review will focus on one of those RTCs known as ataluren that has now completed Phase III clinical studies for DMD and at providing an overview of the different stages that have led to its clinical development for the disease. The impact that this new drug may have on DMD and its future perspectives will also be described, with an emphasis on the importance of further assessing the clinical benefits of this molecule in patients as it becomes available on the market in different countries.

Six-minute walk test is reliable and valid in spinal muscular atrophy

INTRODUCTION

The Six-Minute Walk Test (6MWT) was adopted as a clinical outcome measure for ambulatory spinal muscular atrophy (SMA). However, a systematic review of measurement properties reported significant variation among chronic pediatric conditions. Our purpose was to assess the reliability/validity of the 6MWT in SMA.

METHODS

Thirty participants performed assessments, including the 6MWT, strength, and function. Reproducibility was evaluated by intraclass correlation coefficients. Criterion/convergent validity were determined using Pearson correlation coefficients.

RESULTS

Test-retest reliability was excellent. The 6MWT was associated positively with peak oxygen uptake, Hammersmith Functional Motor Scale Expanded (HFMSE), lower extremity manual muscle testing, knee flexion hand-held dynamometry, and inversely with 10-m walk/run. The 6MWT discriminates between disease severity, unlike the HFMSE.

CONCLUSIONS

This study documents measurement properties of reproducibility, positive criterion validity, and convergent validity with established clinical assessments and reaffirms the value of the 6MWT as a pivotal outcome measure in SMA clinical trials. Muscle Nerve 54: 836-842, 2016.

The 6-minute walk test, motor function measure and quantitative thigh muscle MRI in Becker muscular dystrophy: A cross-sectional study

Becker muscular dystrophy (BMD) has an incidence of 1 in 16 000 male births. This cross-sectional study investigated the relation between validated functional scores and quantitative MRI (qMRI) of thigh muscles in 20 ambulatory BMD patients, aged 18.3-60 years (mean 31.2; SD 11.1). Clinical assessments included the motor function measure (MFM) and its subscales, as well as timed function tests such as the 6-minute walk test (6MWT) and the timed 10-m run/walk test. Quantitative MRI of the thigh muscles included the mean fat fraction (MFF) using a 2-point Dixon (2-PD) technique, and transverse relaxation time (T2) measurements. The mean MFM value was 80.4%, SD 9.44 and the D1 subscore 54.5%, SD 19.9. The median 6MWT was 195m, IQR 160-330.2. The median 10-m run/walk test was 7.4 seconds, IQR 6.1-9.3. The mean fat fraction of the thigh muscles was 55.6%, SD 17.4%, mean T2 relaxation times of all muscles: 69.9 ms, SD 14.4. The flexors had the highest MFF and T2 relaxation times, followed by the extensors and the adductors. MFF and global T2 relaxation times were highly negatively correlated with the MFM total, D1-subscore and 6MWT, and positively correlated with the 10 m run/walk test time (p < 0.01). Age was not correlated with MFF, global T2 relaxation time or clinical assessments. Both MFF and T2 measures in the thigh muscle were well correlated with clinical function in BMD and may serve as a surrogate outcome measure in clinical trials.

Noninvasive Assessment of Neuromuscular Disease in Dogs: Use of the 6-minute Walk Test to Assess Submaximal Exercise Tolerance in Dogs with Centronuclear Myopathy

Background

Noninvasive methods of quantitating exercise tolerance in dogs with neuromuscular disease are needed both for clinical and research use. The 6‐minute walk test (6MWT) has been validated as a reliable test of exercise tolerance in dogs with pulmonary and cardiac disease, but not in dogs with neuromuscular disease.

Hypothesis/Objectives

Distance walked and number of steps taken during 6MWT will differ between Labrador retriever dogs with centronuclear myopathy (CNM) and control (ie, healthy) littermates.

Animals

Eight purebred Labrador retrievers were drawn from a purpose‐bred research colony (status: 3 clear, 2 carrier, and 3 homozygous mutants for the protein tyrosine phosphatase‐like A (PTPLA) gene mutation associated with CNM).

Methods

Pilot, prospective, Case–controlled study. Researchers were blinded to disease status. Each dog was leash‐trained and acclimatized to the testing area (length, 12.8 m). At the start of testing, each animal was fitted with a pedometer, a timer was started, and dogs were allowed to walk at their own pace for 6 minutes. Distance walked and pedometer readings were recorded.

Results

Degree of paresis varied among affected dogs, and was reflected by significant differences in distance walked between CNM‐affected dogs and those with clear and carrier genotypes (P = .048). Pedometer readings did not vary according to genotype (P = .86).

Conclusions

The 6MWT appears to differentiate between the ambulatory capacity of normal and CNM‐affected dogs. Additional studies are needed to confirm this relationship in a larger number of dogs, and to evaluate the ability of the 6MWT to differentiate between dogs with variable severity of neuromuscular disease‐associated exercise intolerance.

The Performance of the Upper Limb scores correlate with pulmonary function test measures and Egen Klassifikation scores in Duchenne muscular dystrophy

The Performance of the Upper Limb scale was developed as an outcome measure specifically for ambulant and non-ambulant patients with Duchenne muscular dystrophy and is implemented in clinical trials needing longitudinal data. The aim of this study is to determine whether this novel tool correlates with functional ability using pulmonary function test, cardiac function test and Egen Klassifikation scale scores as clinical measures. In this cross-sectional study, 43 non-ambulatory Duchenne males from ages 10 to 30 years and on long-term glucocorticoid treatment were enrolled. Cardiac and pulmonary function test results were analyzed to assess cardiopulmonary function, and Egen Klassifikation scores were analyzed to assess functional ability. The Performance of the Upper Limb scores correlated with pulmonary function measures and had inverse correlation with Egen Klassifikation scores. There was no correlation with left ventricular ejection fraction and left ventricular dysfunction. Body mass index and decreased joint range of motion affected total Performance of the Upper Limb scores and should be considered in clinical trial designs.

Multicenter prospective longitudinal study of magnetic resonance biomarkers in a large duchenne muscular dystrophy cohort

OBJECTIVE

The aim of this study was to describe Duchenne muscular dystrophy (DMD) disease progression in the lower extremity muscles over 12 months using quantitative magnetic resonance (MR) biomarkers, collected across three sites in a large cohort.

METHODS

A total of 109 ambulatory boys with DMD (8.7 ± 2.0 years; range, 5.0-12.9) completed baseline and 1-year follow-up quantitative MR imaging (transverse relaxation time constant; MRI-T2 ), MR spectroscopy (fat fraction and (1) H2 O T2 ), and 6-minute walk test (6MWT) measurements. A subset of boys completed additional measurements after 3 or 6 months.

RESULTS

MRI-T2 and fat fraction increased significantly over 12 months in all age groups, including in 5- to 6.9-year-old boys. Significant increases in vastus lateralis (VL) fat fraction were observed in 3 and 6 months. Even in boys whose 6MWT performance improved or remained stable over 1 year, significant increases in MRI-T2 and fat fraction were found. Of all the muscles examined, the VL and biceps femoris long head were the most responsive to disease progression in boys with DMD.

INTERPRETATION

MR biomarkers are responsive to disease progression in 5- to 12.9-year-old boys with DMD and able to detect subclinical disease progression in DMD, even within short (3-6 months) time periods. The measured sensitivity of MR biomarkers in this multicenter study may be critically important to future clinical trials, allowing for smaller sample sizes and/or shorter study windows in this fatal rare disease.

Health-related quality of life and functional changes in DMD: A 12-month longitudinal cohort study

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At baseline, the PedsQL^TM inventories correlated with almost all the functional measures.

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There was a significant decrease between baseline and 12 months on PedsQL^TM GCS.

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This decrement paralleled with the decrement in the functional outcome measures.

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PedsQL^TM correlates with the level of impairment.

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This correlations were not confirmed when 12 month changes are considered.

In Duchenne muscular dystrophy (DMD) little has been reported on the association between clinical outcome measures and patient health-related quality of life (HRQOL) tools. Our study evaluated the relationship between 12 month changes on the Generic Core Scales (GCS), the Multidimensional Fatigue Scale and the Neuromuscular Module of the PedsQL^TM with several outcome measures (6 minute walk test, North Star Ambulatory Assessment and timed items) in ambulatory DMD. Ninety-eight ambulatory DMD in a multicentric setting were included in the study. At baseline, the PedsQL^TM inventories correlated with almost all the functional measures On the Child Self-Report there was a significant decrease between baseline and 12 months on the PedsQL^TM GCS and its first domain, in parallel with the decrement in the functional outcome measures. Correlation between the 12 month changes on the PedsQL^TM inventories and functional measures were almost all negligible. Similar results were obtained on the Parent Proxy-Report.

In conclusion, PedsQL^TM correlates with the level of impairment at baseline, but this does not hold true when 12 month changes are considered. Further studies comparing different tools are needed to better elucidate the complexity of the relationship between HRQOL and functional performances.

Respiratory muscle training (RMT) in late-onset Pompe disease (LOPD): Effects of training and detraining

BACKGROUND

Determine the effects of a 12-week respiratory muscle training (RMT) program in late-onset Pompe disease (LOPD).

METHODS

We investigated the effects of 12-weeks of RMT followed by 3-months detraining using a single-subject A-B-A experimental design replicated across 8 adults with LOPD. To assess maximal volitional respiratory strength, our primary outcomes were maximum inspiratory pressure (MIP) and maximum expiratory pressure (MEP). Effect sizes for changes in MIP and MEP were determined using Cohen's d statistic. Exploratory outcomes targeted motor function, and peak cough flow (PCF) was measured in the last 5 subjects.

RESULTS

From pretest to posttest, all 8 subjects exhibited increases in MIP, and 7 of 8 showed increases in MEP. Effect size data reveal the magnitude of increases in MIP to be large in 4 (d≥1.0) and very large in 4 (d≥2.0), and effect sizes for increases in MEP were large in 1 (d≥1.0) and very large in 6 (d≥2.0). Across participants, pretest to posttest MIP and MEP increased by a mean of 19.6% (sd=9.9) and 16.1% (sd=17.3), respectively. Respiratory strength increases, particularly for the inspiratory muscles, were generally durable to 3-months detraining.

CONCLUSIONS

These data suggest our 12-week RMT program results in large to very large increases in inspiratory and expiratory muscle strength in adults with LOPD. Additionally, increases in respiratory strength appeared to be relatively durable following 3-months detraining. Although additional research is needed, RMT appears to offer promise as an adjunctive treatment for respiratory weakness in LOPD.

[Functional and orthopaedic aspects of dystrophinopathies]

Although the clinical picture and the natural progression of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) differ, borderline forms exist. Classical orthopaedic treatment is based on self-rehabilitation (by the parents and the patient), physical therapy, posture alignment with orthotics, ergotherapy to set up technical aides, notably positioning in an electric wheelchair to provide more satisfactory autonomy. The functional aspect predominates over pure orthopaedics. Although surgical indications have evolved for the lower limbs, pelvic-spinal arthrodesis for treatment of scoliosis remains the reference treatment, but the methods have evolved since the advent of corticotherapy for DMD. Corticotherapy slows the progression of motor deficits, the age at which walking ability is lost is delayed (shifting from 10 years to 13-14 years depending on the studies), scoliosis progresses later, respiratory insufficiency is better controlled, and therefore survival is prolonged (between 20 and 40 years). However, although this functional aspect seems to respond better to the progress in overall treatment, it also results from a multidisciplinary approach to the disease. Nevertheless, assessment is required, not at a time t as reflected by the scales currently in use, but during daily activities as proposed by qualitative and quantitative monitoring seeking to model nyctohemeral functional motor skills. The principle is to characterize the type of activity (sitting, standing, lying down, walking), its duration, its intensity (walking speed), its frequency (number of activity changes, number of walking episodes), and their sequence (temporal sequence, organization of activity variation). The goal is to identify the variety of functional motor skills and their occurrence over time to determine whether treatment contributes a functional benefit and whether this benefit is put into practice daily.

Longitudinal effect of eteplirsen versus historical control on ambulation in Duchenne muscular dystrophy

Objective

To continue evaluation of the long‐term efficacy and safety of eteplirsen, a phosphorodiamidate morpholino oligomer designed to skip DMD exon 51 in patients with Duchenne muscular dystrophy (DMD). Three‐year progression of eteplirsen‐treated patients was compared to matched historical controls (HC).

Methods

Ambulatory DMD patients who were ≥7 years old and amenable to exon 51 skipping were randomized to eteplirsen (30/50mg/kg) or placebo for 24 weeks. Thereafter, all received eteplirsen on an open‐label basis. The primary functional assessment in this study was the 6‐Minute Walk Test (6MWT). Respiratory muscle function was assessed by pulmonary function testing (PFT). Longitudinal natural history data were used for comparative analysis of 6MWT performance at baseline and months 12, 24, and 36. Patients were matched to the eteplirsen group based on age, corticosteroid use, and genotype.

Results

At 36 months, eteplirsen‐treated patients (n = 12) demonstrated a statistically significant advantage of 151m (p < 0.01) on 6MWT and experienced a lower incidence of loss of ambulation in comparison to matched HC (n = 13) amenable to exon 51 skipping. PFT results remained relatively stable in eteplirsen‐treated patients. Eteplirsen was well tolerated. Analysis of HC confirmed the previously observed change in disease trajectory at age 7 years, and more severe progression was observed in patients with mutations amenable to exon skipping than in those not amenable. The subset of patients amenable to exon 51 skipping showed a more severe disease course than those amenable to any exon skipping.

Interpretation

Over 3 years of follow‐up, eteplirsen‐treated patients showed a slower rate of decline in ambulation assessed by 6MWT compared to untreated matched HC. Ann Neurol 2016;79:257–271

Six-minute walk test versus two-minute walk test in children with Duchenne muscular dystrophy: Is more time more information?

BACKGROUND/PURPOSE

The six minute walk test is a widely accepted primary outcome parameter in most studies in Duchenne muscular dystrophy (DMD). To compare information obtained by the six minute walk distance (6MWD) test and the two minute walk distance (2MWD) in patients with DMD, a cohort of 13 voluntary DMD boys did a repeated six minute walking test.

METHODS

Patients had to be ambulatory with a physical disability according to Levels 1-3 on the Vignos-Scale for lower extremity. Measurements were taken at one minute intervals. Reliability was measured by intraclass correlation.

RESULTS

Test-retest reliability for 6MWD and 2MWD in two different age classes was very good for both subgroups. Test-retest-reliability was lower in patients with more advanced disability in both tests. Walking speed remained completely stable from time points 1-6 minutes in the whole study patient collective, which indicates that physical exhaustion is not reached after six minutes even in more disabled patients.

CONCLUSION

Thus the 6MWD in DMD patients does not give additional information as compared to a 2MWD.

Spinal muscular atrophy functional composite score: A functional measure in spinal muscular atrophy

INTRODUCTION

With clinical trials underway, our objective was to construct a composite score of global function that could discriminate among people with spinal muscular atrophy (SMA).

METHODS

Data were collected from 126 participants with SMA types 2 and 3. Scores from the Hammersmith Functional Motor Scale-Expanded and Upper Limb Module were expressed as a percentage of the maximum score and 6-minute walk test as percent of predicted normal distance. A principal component analysis was performed on the correlation matrix for the 3 percentage scores.

RESULTS

The first principal component yielded a composite score with approximately equal weighting of the 3 components and accounted for 82% of the total variability. The SMA functional composite score, an unweighted average of the 3 individual percentage scores, correlated almost perfectly with the first principal component.

CONCLUSIONS

This combination of measures broadens the spectrum of ability that can be quantified in type 2 and 3 SMA patients.

Upper extremity 3-dimensional reachable workspace analysis in dystrophinopathy using Kinect

INTRODUCTION

An innovative upper extremity 3-dimensional (3D) reachable workspace outcome measure acquired using the Kinect sensor is applied toward Duchenne/Becker muscular dystrophy (DMD/BMD). The validity, sensitivity, and clinical meaningfulness of this novel outcome measure are examined.

METHODS

Upper extremity function assessment (Brooke scale and NeuroQOL questionnaire) and Kinect-based reachable workspace analyses were conducted in 43 individuals with dystrophinopathy (30 DMD and 13 BMD, aged 7-60 years) and 46 controls (aged 6-68 years).

RESULTS

The reachable workspace measure reliably captured a wide range of upper extremity impairments encountered in both pediatric and adult, as well as ambulatory and non-ambulatory individuals with dystrophinopathy. Reduced reachable workspaces were noted for the dystrophinopathy cohort compared with controls, and they correlated with Brooke grades. In addition, progressive reduction in reachable workspace correlated directly with worsening ability to perform activities of daily living, as self-reported on the NeuroQOL.

CONCLUSION

This study demonstrates the utility and potential of the novel sensor-acquired reachable workspace outcome measure in dystrophinopathy.

New approaches to the treatment of orphan genetic disorders: Mitigating molecular pathologies using chemicals

With the advance and popularization of molecular techniques, the identification of genetic mutations that cause diseases has increased dramatically. Thus, the number of laboratories available to investigate a given disorder and the number of subsequent diagnosis have increased over time. Although it is necessary to identify mutations and provide diagnosis, it is also critical to develop specific therapeutic approaches based on this information. This review aims to highlight recent advances in mutation-targeted therapies with chemicals that mitigate mutational pathology at the molecular level, for disorders that, for the most part, have no effective treatment. Currently, there are several strategies being used to correct different types of mutations, including the following: the identification and characterization of translational readthrough compounds; antisense oligonucleotide-mediated splicing redirection; mismatch repair; and exon skipping. These therapies and other approaches are reviewed in this paper.

Circulating Biomarkers for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy is the most common form of muscular dystrophy. Genetic and biochemical research over the years has characterized the cause, pathophysiology and development of the disease providing several potential therapeutic targets and/or biomarkers. High throughput - omic technologies have provided a comprehensive understanding of the changes occurring in dystrophic muscles. Murine and canine animal models have been a valuable source to profile muscles and body fluids, thus providing candidate biomarkers that can be evaluated in patients. This review will illustrate known circulating biomarkers that could track disease progression and response to therapy in patients affected by Duchenne muscular dystrophy. We present an overview of the transcriptomic, proteomic, metabolomics and lipidomic biomarkers described in literature. We show how studies in muscle tissue have led to the identification of serum and urine biomarkers and we highlight the importance of evaluating biomarkers as possible surrogate endpoints to facilitate regulatory processes for new medicinal products.

Elosulfase Alfa: a review of its use in patients with mucopolysaccharidosis type IVA (Morquio A syndrome)

Elosulfase alfa (Vimizim(®)) is a recombinant form of the human lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS) that is lacking in patients with mucopolysaccharidosis type IVA (MPS IVA; Morquio A syndrome). It is the first, and currently only, disease-specific treatment option for this very rare, progressively degenerative, autosomal-recessive lysosomal storage disorder. Enzyme replacement therapy with elosulfase alfa aims to restore GALNS activity, thereby preventing the accumulation of keratan sulfate (KS) and chondroitin-6-sulfate in lysosomal compartments of cells that results in the clinical manifestations of MPS IVA. In clinical trials in children and adults with MPS IVA, intravenous elosulfase alfa 2 mg/kg/week provided significant and sustained improvements in urinary levels of KS (a pharmacodynamic biomarker for the disease). In the key placebo-controlled, 24-week, phase 3 trial in patients with MPS IVA aged ≥5 years, elosulfase alfa 2 mg/kg/week significantly improved endurance [least squares mean placebo-adjusted change from baseline in 6-min walk test distance 22.5 m (95 % CI 4.0-40.9)]. Infusion-associated reactions, the primary tolerability issue associated with elosulfase alfa, are generally mild to moderate in severity, self-limiting, and manageable. In the absence of a cure, GALNS enzyme replacement therapy with elosulfase alfa is an important achievement in the treatment of MPS IVA.

Galectin-1 Protein Therapy Prevents Pathology and Improves Muscle Function in the mdx Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a fatal neuromuscular disease caused by mutations in the dystrophin gene, leading to the loss of a critical component of the sarcolemmal dystrophin glycoprotein complex. Galectin-1 is a small 14 kDa protein normally found in skeletal muscle and has been shown to be a modifier of immune response, muscle repair, and apoptosis. Galectin-1 levels are elevated in the muscle of mouse and dog models of DMD. Together, these findings led us to hypothesize that Galectin-1 may serve as a modifier of disease progression in DMD. To test this hypothesis, recombinant mouse Galectin-1 was produced and used to treat myogenic cells and the mdx mouse model of DMD. Here we show that intramuscular and intraperitoneal injections of Galectin-1 into mdx mice prevented pathology and improved muscle function in skeletal muscle. These improvements were a result of enhanced sarcolemmal stability mediated by elevated utrophin and α7β1 integrin protein levels. Together our results demonstrate for the first time that Galectin-1 may serve as an exciting new protein therapeutic for the treatment of DMD.