The IAAM LTBP4 Haplotype is Protective Against Dystrophin-Deficient Cardiomyopathy.

Background: Dilated cardiomyopathy (DCM) is a major complication of, and leading cause of mortality in Duchenne muscular dystrophy (DMD). Its severity, age at onset, and rate of progression display wide variability, whose molecular bases have been scarcely elucidated. Potential DCM-modifying factors include glucocorticoid (GC) and cardiological treatments, DMD mutation type and location, and variants in other genes. Methods and Results: We retrospectively collected 3138 echocardiographic measurements of left ventricular ejection fraction (EF), shortening fraction (SF), and end-diastolic volume (EDV) from 819 DMD participants, 541 from an Italian multicentric cohort and 278 from the Cooperative International Neuromuscular Group Duchenne Natural History Study (CINRG-DNHS). Using generalized estimating equation (GEE) models, we estimated the yearly rate of decrease of EF (-0.80%) and SF (-0.41%), while EDV increase was not significantly associated with age. Utilizing a multivariate generalized estimating equation (GEE) model we observed that mutations preserving the expression of the C-terminal Dp71 isoform of dystrophin were correlated with decreased EDV (-11.01 mL/m2, p = 0.03) while for dp116 were correlated with decreased EF (-4.14%, p = <0.001). The rs10880 genotype in the LTBP4 gene, previously shown to prolong ambulation, was also associated with increased EF and decreased EDV (+3.29%, p = 0.002, and -10.62 mL/m2, p = 0.008) with a recessive model. Conclusions: We quantitatively describe the progression of systolic dysfunction progression in DMD, confirm the effect of distal dystrophin isoform expression on the dystrophin-deficient heart, and identify a strong effect of LTBP4 genotype of DCM in DMD.

Parkinsonism may aggravate dysphagia in myotonic dystrophy type 1: two case reports.

Introduction: Weakness of trunk muscles, fatigue and reduced mobility are features of myotonic dystrophy type 1 (DM1) and may also characterize patients with extrapyramidal disorders.Dysphagia is common in DM1 and parkinsonism and can be predominant compared to other symptom, often requiring surgical tratment. Methods: We describe two cases of patients with DM1 and parkinsonism who arrived at our Center for worsening dysphagia and who showed very similar and peculiar clinical features. Case reports: The first patient presented initially at the outpatient clinic reporting a 7 year history of progressive difficulties in swallowing and movement slowness. Neurologic examination showed a general bradykinesia, plastic rigidity of upper limbs, diffuse hypotrophy and deep tendon reflexes weakness. MRI scan of brain and spine was unremarkable, but neurophysiological evaluation revealed diffuse myotonic discharges on distal limb muscles. Genetic testing confirmed DM1 diagnosis (CTG range E1).The second patient, presented with an initial diagnosis of parkinsonism due to a 10 years history of gait impairment, generalized weakness and dysphagia. Due to low back pain a neurophysiological study was performed after 5 years from diagnosis of parkinsonism detecting diffuse myotonic discharges and genetic testing confirmed diagnosis of DM1 (CTG range E2).Percutaneous endoscopic gastrostomy (PEG) was severe and burdensome for both patients.To date, only one case of molecularly confirmed DM1 along with parkinsonism has been described. We have described two cases of DM1 and parkinsonism in which swallowing function has been affected by a synergic effect triggered by both muscle condition and extrapyramidal disease.

Facial nerve vulnerability in spinal muscular atrophy and motor unit number index of the orbicularis oculi muscle.

INTRODUCTION/AIMS: Measures for assessing cranial nerve vulnerability in spinal muscular atrophy (SMA) have not yet been determined. Motor unit number index (MUNIX) studies have shown correlations with disease severity but have been used only in limb muscles. In the present study, we explore facial nerve response, MUNIX, and motor unit size index (MUSIX) of the orbicularis oculi muscle in a cohort of patients with SMA. METHODS: Facial nerve response (measured as compound muscle action potential, CMAP), MUNIX, and MUSIX of the orbicularis oculi muscle were cross-sectionally recorded in patients with SMA and compared to healthy control subjects (HCs). Active maximum mouth opening (aMMO) was also measured at baseline in our SMA cohort. RESULTS: Thirty-seven patients with SMA (21 SMA II; 16 SMA III) and 27 HCs were recruited. CMAP of the facial nerve and MUNIX of orbicularis oculi proved to be feasible and well tolerated techniques. CMAP amplitude and MUNIX scores were significantly lower in patients with SMA compared to HCs (p < .0001). Both MUNIX and CMAP amplitude were significantly higher in patients with SMA III compared to SMA II. No significant difference emerged comparing CMAP amplitude, MUNIX and MUSIX scores between those with different functional status or nusinersen treatment. DISCUSSION: Our results provide neurophysiological evidence of facial nerve and muscle involvement in patients with SMA. CMAP of the facial nerve and MUNIX of orbicularis oculi showed high accuracy in discriminating between the various subtypes of SMA and in quantifying the motor unit loss of the facial nerve.

TeleNEwCARe: An Italian case-control telegenetics study in patients with Hereditary NEuromuscular and CARdiac diseases.

Telemedicine provides healthcare services remotely and represents a fundamental resource for the management of rare and fragile patients. Tele-health implementation is a main objective of the European Reference Networks (ERNs) mission to accelerate diagnosis for rare diseases. TeleNewCARe is a pilot case-control project which evaluates the efficacy and satisfaction of telegenetics for neuromuscular and cardiac adult patients, compared to face-to-face genetic counselling. The virtual sessions were co-hosted by a medical geneticist and a neurologist/cardiologist. Specific questionnaires (Clinical Genetics Satisfaction Questionnaire (CGS), Telemedicine Satisfaction Questionnaire (TSQ) and a Satisfaction Questionnaire for medical geneticists) were used to assess the effectiveness and fulfilment of telecounselling, both for patients and health care providers. Satisfaction expressed for telegenetics did not significantly differ from face-to-face counselling. The virtually enrolled patients declared they had the possibility to relate confidentially with the specialists, to share information and to be informed in an exhaustive way about their disease. Almost all patients declared themselves willing to reuse the telecounselling in the future. The multidisciplinary care was perceived as a significant added value. No overt technical problems were reported although the need for digital skills and tools can limit patients' compliance. Our experience supports telegenetics as a valid alternative to traditional genetic counselling in cardiac and neuromuscular patients. This innovative approach facilitates multidisciplinary care, grants a periodical follow up, without forcing patients to discomfortable travelling, and allows to maintain expert care. This result meets the ERNs needs to reduce patients' burden to access and monitor their healthcare.

Anti-HMGCR myopathy: barriers to prompt recognition.

Anti-HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase) myopathy is an immune-mediated necrotising myopathy. Atypical presentations hinder its recognition and its prompt treatment. We present two patients with atypical clinical or pathological features. A 45-year-old woman had an asymptomatic serum creatine kinase (CK) of ~10 000 IU/L and muscle biopsy showing minimal changes. She then developed slowly progressive proximal weakness, diagnosed as limb-girdle muscular dystrophy but with negative genetics. Twelve years later, now with severe proximal weakness, her MR scan of muscle showed diffuse asymmetrical fatty degeneration, with conspicuous hyperintense STIR signal abnormalities. HMGCR antibodies were positive and she partially improved with immunosuppression. The second patient developed slowly progressive proximal limb weakness with a high serum CK (~4000 IU/L); muscle biopsy showed a lymphocyte infiltrate with angiocentric distribution suggesting vasculitis. Serum HMGCR antibodies were positive. Anti-HMGCR myopathy can present as a slowly progressive myopathy with atypical pathology. HMGCR antibody screening is indicated for people with suspected limb-girdle muscular dystrophy or atypical inflammatory muscle conditions.

Assessment of Respiratory Function and Need for Noninvasive Ventilation in a Cohort of Patients with Myotonic Dystrophy Type 1 Followed at One Single Expert Center.

Introduction: Respiratory insufficiency is one of the main causes of death in myotonic dystrophy type 1 (DM1). Although there is general consensus that these patients have a restrictive ventilatory pattern, hypoventilation, chronic hypercapnia, and sleep disturbances, the prevalence of respiratory disease and indication for the effects of noninvasive ventilation (NIV) need to be further explored. Objectives: To describe respiratory function and need for NIV at baseline and over time in a cohort of adult patients with DM1. Methods: A total of 151 adult patients with DM1 were subjected to arterial blood gas analysis, sitting and supine forced vital capacity (FVC), peak cough expiratory flow (PCEF), nocturnal oximetry, and maximal inspiratory pressure and expiratory pressure (MIP/PEP). Results: On first assessment, 84 of 151 had normal respiratory function (median age: 38 years, median BMI: 23.9, and median disease duration: 11 years); 67 received an indication to use NIV (median age: 49 years, median BMI: 25,8, and median disease duration: 14 years). After a median time of 3.85 years, 43 patients were lost to follow-up; 9 of 84 required NIV; only 17 of 67 with the new NIV prescription were adherent. Conclusions: We provide additional data on the natural history of respiratory function decline and treatment adherence in a relatively large cohort of well-characterized patients with DM1. A high proportion (28%) was lost to follow-up. A minority (11%) required NIV, and only 25% were treatment adherent, irrespective of specific demographics and respiratory features. Our results also confirm previous findings, showing that age, disease duration, and higher BMIs are predisposing factors for respiratory impairment.

Functional outcome measures in young, steroid-naïve boys with Duchenne muscular dystrophy.

The purpose of this study was to quantitate motor performance in 196 genetically confirmed steroid-naïve boys with Duchenne muscular dystrophy (DMD), to evaluate the test-retest reliability of measures of motor performance in young DMD boys, and to assess correlations among the different functional outcomes including timed tests. Boys aged 4-7 years were recruited in the FOR-DMD study, a comparative effectiveness study of different steroid regimens in DMD. Eligible boys had to be able to rise from the floor independently and to perform pulmonary function testing consistently. The boys were evaluated with standardized assessments at the screening and baseline visits at 32 sites in 5 countries (US, UK, Canada, Italy, Germany). Assessments included timed rise from floor, timed 10 m walk/run, six-minute walk distance, North Star Ambulatory Assessment (NSAA) and forced vital capacity (FVC). Mean age at baseline was 5.9 years (range 4.1-8.1 years). Test-retest reliability was high for functional assessments, regardless of time lag between assessments (up to 90 days) and for the majority of age groups. Correlations were strong among the functional measures and timed tests, less so with FVC. Physiotherapy measures are reliable in a young, steroid-naïve population and rise from floor velocity appears to be a sensitive measure of strength in this population.

Body composition and myokines in a cohort of patients with Becker muscular dystrophy.

INTRODUCTION/AIMS: Becker muscular dystrophy (BMD) is an X-linked disease leading to muscle wasting and weakness. The decrease in lean body mass (LBM) in Duchenne muscular dystrophy, has shown correlation with loss of muscle function and bone density (BD). Myokines (including irisin) are hormones secreted by skeletal muscle that allow crosstalk between muscle and bone. The present study analyzed body composition and circulating myokine levels in a cohort of BMD patients; moreover, the association between dual energy X-ray absorptiometry (DXA) parameters, functional motor assessments, and myokine levels was investigated. METHODS: All patients underwent DXA, blood samples for myokine assays, and functional motor assessments. A group of healthy controls (HCs) was also included. RESULTS: Thirty BMD patients, median age at evaluation 36.0 y [26.0-41.0], were included. Twenty-nine patients underwent whole-body DXA. Median value of total body Z-score was -0.70. The prevalence of low skeletal muscle mass defined as appendicular skeletal muscle mass index (ASMMI) < 7.59 kg/m2 was 83%. Irisin levels were significantly lower in BMD compared to HCs (p = .03). All DXA parameters showed significant correlation with the functional motor assessments, in particular the h2 -standardized lean mass lower limb index (p = .0006); h2 -standardized total fat mass showed negative correlations with North Star Ambulatory Assessment and 6 min walk test (p = .03). DISCUSSION: DXA is a useful tool to evaluate body composition in BMD patients; the decrease in BD and LBM is associated with a reduction of motor function in BMD.

RNA-seq in DMD urinary stem cells recognized muscle-related transcription signatures and addressed the identification of atypical mutations by whole-genome sequencing.

Urinary stem cells (USCs) are a non-invasive, simple, and affordable cell source to study human diseases. Here we show that USCs are a versatile tool for studying Duchenne muscular dystrophy (DMD), since they are able to address RNA signatures and atypical mutation identification. Gene expression profiling of DMD individuals' USCs revealed a profound deregulation of inflammation, muscle development, and metabolic pathways that mirrors the known transcriptional landscape of DMD muscle and worsens following USCs' myogenic transformation. This pathogenic transcription signature was reverted by an exon-skipping corrective approach, suggesting the utility of USCs in monitoring DMD antisense therapy. The full DMD transcript profile performed in USCs from three undiagnosed DMD individuals addressed three splicing abnormalities, which were decrypted and confirmed as pathogenic variations by whole-genome sequencing (WGS). This combined genomic approach allowed the identification of three atypical and complex DMD mutations due to a deep intronic variation and two large inversions, respectively. All three mutations affect DMD gene splicing and cause a lack of dystrophin protein production, and one of these also generates unique fusion genes and transcripts. Further characterization of USCs using a novel cell-sorting technology (Celector) highlighted cell-type variability and the representation of cell-specific DMD isoforms. Our comprehensive approach to USCs unraveled RNA, DNA, and cell-specific features and demonstrated that USCs are a robust tool for studying and diagnosing DMD.

Whole-body muscle MRI in McArdle disease.

This study describes muscle involvement on whole-body MRI (WB-MRI) scans at different stages of McArdle disease. WB-MRI was performed on fifteen genetically confirmed McArdle disease patients between ages 25 to 80. The degree of fatty substitution was scored for 60 muscles using Mercuri's classification. All patients reported an intolerance to exercise and episodes of rhabdomyolysis. A mild fixed muscle weakness was observed in 13/15 patients with neck flexor weakness in 7/15 cases, and proximal muscle weakness in 6/15 cases. A moderate scapular winging was observed in five patients. A careful review of the MRI scans, as well as hierarchical clustering of patients by Mercuri scores, pointed out recurrent muscle changes particularly in the subscapularis, anterior serratus, erector spinae and quadratus femoris muscles. WB-MRI imaging provides clinically relevant information and is a useful tool to orient toward the diagnosis of McArdle disease.

Circulating Biomarkers in Neuromuscular Disorders: What Is Known, What Is New.

The urgent need for new therapies for some devastating neuromuscular diseases (NMDs), such as Duchenne muscular dystrophy or amyotrophic lateral sclerosis, has led to an intense search for new potential biomarkers. Biomarkers can be classified based on their clinical value into different categories: diagnostic biomarkers confirm the presence of a specific disease, prognostic biomarkers provide information about disease course, and therapeutic biomarkers are designed to predict or measure treatment response. Circulating biomarkers, as opposed to instrumental/invasive ones (e.g., muscle MRI or nerve ultrasound, muscle or nerve biopsy), are generally easier to access and less "time-consuming". In addition to well-known creatine kinase, other promising molecules seem to be candidate biomarkers to improve the diagnosis, prognosis and prediction of therapeutic response, such as antibodies, neurofilaments, and microRNAs. However, there are some criticalities that can complicate their application: variability during the day, stability, and reliable performance metrics (e.g., accuracy, precision and reproducibility) across laboratories. In the present review, we discuss the application of biochemical biomarkers (both validated and emerging) in the most common NMDs with a focus on their diagnostic, prognostic/predictive and therapeutic application, and finally, we address the critical issues in the introduction of new biomarkers.

Neurophysiological indices in amyotrophic lateral sclerosis correlate with functional outcome measures, staging and disease progression.

OBJECTIVE: This study examined neurophysiological (NI), split-hand (SI) and split-leg (SLI) index in patients with amyotrophic lateral sclerosis (ALS), and their correlation with functional status, disease duration, staging and survival. METHODS: Eighty-two patients underwent nerve conduction study to analyze NI, SI and SLI. Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R), disease progression rate (ΔFS), Milano-Torino (MiToS) and King's staging systems, Forced Vital Capacity (FVC), and survival data were collected. RESULTS: Both NI and SI indices were significantly associated with ALSFRS-R, MiToS, King's and FVC. Slow progressor patients (ΔFS < 0.5) reported a significantly higher NI and SI values compared to both normal (0.5 ≤ ΔFS < 1.00) and fast progressors (ΔFS ≥ 1.0). After dichotomizing patients in slow progressors (ΔFS < 0.5) and not-slow progressors (ΔFS ≥ 0.5), a combination of SI index and disease duration revealed to be the best prediction model to discriminate patients in accordance with their disease progression (c-index: 0.92), leading to a new prognostic index: the 'Split-Hand prognostic index' (SHpi). CONCLUSION: SI and NI are correlated with functional status and FVC. SHpi index could represent an useful tool to discriminate patients in accordance with their disease progression. SIGNIFICANCE: These data provide novel evidence of neurophysiological indices as promising biomarkers in ALS.

Facilitations and Hurdles of Genetic Testing in Neuromuscular Disorders.

Neuromuscular disorders (NMDs) comprise a heterogeneous group of disorders that affect about one in every thousand individuals worldwide. The vast majority of NMDs has a genetic cause, with about 600 genes already identified. Application of genetic testing in NMDs can be useful for several reasons: correct diagnostic definition of a proband, extensive familial counselling to identify subjects at risk, and prenatal diagnosis to prevent the recurrence of the disease; furthermore, identification of specific genetic mutations still remains mandatory in some cases for clinical trial enrollment where new gene therapies are now approaching. Even though genetic analysis is catching on in the neuromuscular field, pitfalls and hurdles still remain and they should be taken into account by clinicians, as for example the use of next generation sequencing (NGS) where many single nucleotide variants of "unknown significance" can emerge, complicating the correct interpretation of genotype-phenotype relationship. Finally, when all efforts in terms of molecular analysis have been carried on, a portion of patients affected by NMDs still remain "not genetically defined". In the present review we analyze the evolution of genetic techniques, from Sanger sequencing to NGS, and we discuss "facilitations and hurdles" of genetic testing which must always be balanced by clinicians, in order to ensure a correct diagnostic definition, but taking always into account the benefit that the patient could obtain especially in terms of "therapeutic offer".

Muscle MRI in two SMA patients on nusinersen treatment: A two years follow-up.

INTRODUCTION: The effects of nusinersen in adults with SMA rely on neuromotor function scales and qualitative assessments. There are limited clinical or imaging data on muscle changes over time. METHODS: Two adult SMA patients underwent clinical assessments including measures of upper and lower limb function with Revised Upper Limb Module (RULM) and Hammersmith Function Motor Scale Expanded (HFMSE); both patients were also studied with whole-body muscle MRI (T1-weighted and Diffusion Tensor Imaging/DTI sequences), at baseline and after 10 and 24 months from the beginning of treatment with nusinersen. RESULTS: After two years of treatment, HFMSE and RULM scores were stable in both patients. DTI sequences revealed an increased number, length and organization of muscle fiber tracks, and Fractional Anisotropy (FA) values showed a significant reduction after 10 and 24 months from baseline, in their corresponding maps. DISCUSSION: Muscle DTI imaging seems to play an interesting role to monitor treatment effects over time in adult SMA patients.

Emerging Drugs for the Treatment of Amyotrophic Lateral Sclerosis: A Focus on Recent Phase 2 Trials.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease involving both upper and lower motor neurons and resulting in increasing disability and death 3-5 years after onset of symptoms. Over 40 large clinical trials for ALS have been negative, except for Riluzole that offers a modest survival benefit, and Edaravone that modestly reduces disease progression in patients with specific characteristics. Thus, the discovery of efficient disease modifying therapy is an urgent need. AREAS COVERED: Although the cause of ALS remains unclear, many studies have demonstrated that neuroinflammation, proteinopathies, glutamate-induced excitotoxicity, microglial activation, oxidative stress, and mitochondrial dysfunction may play a key role in the pathogenesis. This review highlights recent discoveries relating to these diverse mechanisms and their implications for the development of therapy. Ongoing phase 2 clinical trials aimed to interfere with these pathophysiological mechanisms are discussed. EXPERT OPINION: This review describes the challenges that the discovery of an efficient drug therapy faces and how these issues may be addressed. With the continuous advances coming from basic research, we provided possible suggestions that may be considered to improve performance of clinical trials and turn ALS research into a 'fertile ground' for drug development for this devastating disease.

Genetic modifiers of respiratory function in Duchenne muscular dystrophy.

OBJECTIVE: Respiratory insufficiency is a major complication of Duchenne muscular dystrophy (DMD). Its progression shows considerable interindividual variability, which has been less thoroughly characterized and understood than in skeletal muscle. We collected pulmonary function testing (PFT) data from a large retrospective cohort followed at Centers collaborating in the Italian DMD Network. Furthermore, we analyzed PFT associations with different DMD mutation types, and with genetic variants in SPP1, LTBP4, CD40, and ACTN3, known to modify skeletal muscle weakness in DMD. Genetic association findings were independently validated in the Cooperative International Neuromuscular Research Group Duchenne Natural History Study (CINRG-DNHS). METHODS AND RESULTS: Generalized estimating equation analysis of 1852 PFTs from 327 Italian DMD patients, over an average follow-up time of 4.5 years, estimated that forced vital capacity (FVC) declined yearly by -4.2%, forced expiratory volume in 1 sec by -5.0%, and peak expiratory flow (PEF) by -2.9%. Glucocorticoid (GC) treatment was associated with higher values of all PFT measures (approximately + 15% across disease stages). Mutations situated 3' of DMD intron 44, thus predicted to alter the expression of short dystrophin isoforms, were associated with lower (approximately -6%) PFT values, a finding independently validated in the CINRG-DNHS. Deletions amenable to skipping of exon 51 and 53 were independently associated with worse PFT outcomes. A meta-analysis of the two cohorts identified detrimental effects of SPP1 rs28357094 and CD40 rs1883832 minor alleles on both FVC and PEF. INTERPRETATION: These findings support GC efficacy in delaying respiratory insufficiency, and will be useful for the design and interpretation of clinical trials focused on respiratory endpoints in DMD.

European muscle MRI study in limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A).

BACKGROUND: Limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A) is a progressive myopathy caused by deficiency of calpain 3, a calcium-dependent cysteine protease of skeletal muscle, and it represents the most frequent type of LGMD worldwide. In the last few years, muscle magnetic resonance imaging (MRI) has been proposed as a tool for identifying patterns of muscular involvement in genetic disorders and as a biomarker of disease progression in muscle diseases. In this study, 57 molecularly confirmed LGMDR1 patients from a European cohort (age range 7-78 years) underwent muscle MRI and a global evaluation of functional status (Gardner-Medwin and Walton score and ability to raise the arms). RESULTS: We confirmed a specific pattern of fatty substitution involving predominantly the hip adductors and hamstrings in lower limbs. Spine extensors were more severely affected than spine rotators, in agreement with higher incidence of lordosis than scoliosis in LGMDR1. Hierarchical clustering of lower limb MRI scores showed that involvement of anterior thigh muscles discriminates between classes of disease progression. Severity of muscle fatty substitution was significantly correlated with CAPN3 mutations: in particular, patients with no or one "null" alleles showed a milder involvement, compared to patients with two null alleles (i.e., predicting absence of calpain-3 protein). Expectedly, fat infiltration scores strongly correlated with functional measures. The "pseudocollagen" sign (central areas of sparing in some muscle) was associated with longer and more severe disease course. CONCLUSIONS: We conclude that skeletal muscle MRI represents a useful tool in the diagnostic workup and clinical management of LGMDR1.

Whole-Body Muscle Magnetic Resonance Imaging in Glycogen-Storage Disease Type III.

INTRODUCTION: The main objective of this study was to describe muscle involvement on whole-body magnetic resonance imaging scans in adults at different stages of glycogen-storage disease type III (GSDIII). METHODS: Fifteen patients, 16-59 years of age, were examined on a 3-T system. The examinations consisted of coronal and axial T1-weighted images or fat images with a Dixon technique, and were scored for 47 muscles using Mercuri's classification. Muscle changes consisted of internal bright signals of fatty replacement. RESULTS: Distribution across muscles showed predominant signal alteration in the lower limbs and postural muscles. This finding is consistent with the overall clinical presentation of GSDIII and the results of heatmap scores. Review of the MRI scans provided new information regarding recurrent muscle changes, particularly in the soleus, gastrocnemius medial head, and thoracic extensor muscles. DISCUSSION: Whole-body muscle imaging provides clinically relevant information regarding muscle involvement in GSDIII. A severity score may contribute to improved patient management. Muscle Nerve, 2019.