Becker-type muscular dystrophy

Vamorolone improves Becker muscular dystrophy and increases dystrophin protein in bmx model mice

There is no approved therapy for Becker muscular dystrophy (BMD), a genetic muscle disease caused by in-frame dystrophin deletions. We previously developed the dissociative corticosteroid vamorolone for treatment of the allelic, dystrophin-null disease Duchenne muscular dystrophy. We hypothesize vamorolone can treat BMD by safely reducing inflammatory signaling in muscle and through a novel mechanism of increasing dystrophin protein via suppression of dystrophin-targeting miRNAs. Here, we test this in the bmx mouse model of BMD. Daily oral treatment with vamorolone or prednisolone improves bmx grip strength and hang time phenotypes. Both drugs reduce myofiber size and decrease the percentage of centrally nucleated fibers. Vamorolone shows improved safety versus prednisolone by avoiding or reducing key side effects to behavior and growth. Intriguingly, vamorolone increases dystrophin protein in both heart and skeletal muscle. These data indicate that vamorolone, nearing approval for Duchenne, shows efficacy in bmx mice and therefore warrants clinical investigation in BMD.

Diffusion-tensor magnetic resonance imaging captures increased skeletal muscle fibre diameters in Becker muscular dystrophy

BACKGROUND

Becker muscular dystrophy (BMD) is an X-linked disorder characterized by slow, progressive muscle damage and muscle weakness. Hallmarks include fibre-size variation and replacement of skeletal muscle with fibrous and adipose tissues, after repeated cycles of regeneration. Muscle histology can detect these features, but the required biopsies are invasive, are difficult to repeat and capture only small muscle volumes. Diffusion-tensor magnetic resonance imaging (DT-MRI) is a potential non-invasive alternative that can calculate muscle fibre diameters when applied with the novel random permeable barrier model (RPBM). In this study, we assessed muscle fibre diameters using DT-MRI in BMD patients and healthy controls and compared these with histology.

METHODS

We included 13 BMD patients and 9 age-matched controls, who underwent water-fat MRI and DT-MRI at multiple diffusion times, allowing RPBM parameter estimation in the lower leg muscles. Tibialis anterior muscle biopsies were taken from the contralateral leg in 6 BMD patients who underwent DT-MRI and from an additional 32 BMD patients and 15 healthy controls. Laminin and Sirius-red stainings were performed to evaluate muscle fibre morphology and fibrosis. Twelve ambulant patients from the MRI cohort underwent the North Star ambulatory assessment, and 6-min walk, rise-from-floor and 10-m run/walk functional tests.

RESULTS

RPBM fibre diameter was significantly larger in BMD patients (P = 0.015): mean (SD) = 68.0 (25.3) μm versus 59.4 (19.2) μm in controls. Inter-muscle differences were also observed (P ≤ 0.002). Both inter- and intra-individual RPBM fibre diameter variability were similar between groups. Laminin staining agreed with the RPBM, showing larger median fibre diameters in patients than in controls: 72.5 (7.9) versus 63.2 (6.9) μm, P = 0.006. However, despite showing similar inter-individual variation, patients showed more intra-individual fibre diameter variability than controls-mean variance (SD) = 34.2 (7.9) versus 21.4 (6.9) μm, P < 0.001-and larger fibrosis areas: median (interquartile range) = 21.7 (5.6)% versus 14.9 (3.4)%, P < 0.001. Despite good overall agreement of RPBM and laminin fibre diameters, they were not associated in patients who underwent DT-MRI and muscle biopsy, perhaps due to lack of colocalization of DT-MRI with biopsy samples.

CONCLUSIONS

DT-MRI RPBM metrics agree with histology and can quantify changes in muscle fibre size that are associated with regeneration without the need for biopsies. They therefore show promise as imaging biomarkers for muscular dystrophies.

The X-linked Becker muscular dystrophy (bmx) mouse models Becker muscular dystrophy via deletion of murine dystrophin exons 45-47

BACKGROUND

Becker muscular dystrophy (BMD) is a genetic neuromuscular disease of growing importance caused by in-frame, partial loss-of-function mutations in the dystrophin (DMD) gene. BMD presents with reduced severity compared with Duchenne muscular dystrophy (DMD), the allelic disorder of complete dystrophin deficiency. Significant therapeutic advancements have been made in DMD, including four FDA-approved drugs. BMD, however, is understudied and underserved-there are no drugs and few clinical trials. Discordance in therapeutic efforts is due in part to lack of a BMD mouse model which would enable greater understanding of disease and de-risk potential therapeutics before first-in-human trials. Importantly, a BMD mouse model is becoming increasingly critical as emerging DMD dystrophin restoration therapies aim to convert a DMD genotype into a BMD phenotype.

METHODS

We use CRISPR/Cas9 technology to generate bmx (Becker muscular dystrophy, X-linked) mice, which express an in-frame ~40 000 bp deletion of exons 45-47 in the murine Dmd gene, reproducing the most common BMD patient mutation. Here, we characterize muscle pathogenesis using molecular and histological techniques and then test skeletal muscle and cardiac function using muscle function assays and echocardiography.

RESULTS

Overall, bmx mice present with significant muscle weakness and heart dysfunction versus wild-type (WT) mice, despite a substantial improvement in pathology over dystrophin-null mdx52 mice. bmx mice show impaired motor function in grip strength (-39%, P < 0.0001), wire hang (P = 0.0025), and in vivo as well as ex vivo force assays. In aged bmx, echocardiography reveals decreased heart function through reduced fractional shortening (-25%, P = 0.0036). Additionally, muscle-specific serum CK is increased >60-fold (P < 0.0001), indicating increased muscle damage. Histologically, bmx muscles display increased myofibre size variability (minimal Feret's diameter: P = 0.0017) and centrally located nuclei indicating degeneration/regeneration (P < 0.0001). bmx muscles also display dystrophic pathology; however, levels of the following parameters are moderate in comparison with mdx52: inflammatory/necrotic foci (P < 0.0001), collagen deposition (+1.4-fold, P = 0.0217), and sarcolemmal damage measured by intracellular IgM (P = 0.0878). Like BMD patients, bmx muscles show reduced dystrophin protein levels (~20-50% of WT), whereas Dmd transcript levels are unchanged. At the molecular level, bmx muscles express increased levels of inflammatory genes, inflammatory miRNAs and fibrosis genes.

CONCLUSIONS

The bmx mouse recapitulates BMD disease phenotypes with histological, molecular and functional deficits. Importantly, it can inform both BMD pathology and DMD dystrophin restoration therapies. This novel model will enable further characterization of BMD disease progression, identification of biomarkers, identification of therapeutic targets and new preclinical drug studies aimed at developing therapies for BMD patients.

Large scale population screening for Duchenne muscular dystrophy - Predictable and unpredictable challenges

Objective

Large deletions and duplications account for 65%–80% of pathogenic Duchenne muscular dystrophy (DMD) variants. A nationwide carrier screening for DMD was initiated in Israel in 2020. We assessed the carrier rate and spectrum of variants detected in a cohort of women screened for DMD carrier status and analyzed screening efficacy and challenges related to DMD population screening.

Methods

A cohort of 12,362 women were tested at a single institute using multiplex ligation‐dependent probe amplification based copy number analysis of the 79 DMD exons. Consecutive sequencing of the primer region was performed when a single exon deletion was suspected.

Results

Deletions involving multiple exons were detected in seven cases and duplications involving multiple exons were found in four. Of these, nine were pathogenic based on previous reports and familial segregation testing, translating to a carrier rate of 1:1374. A family history was reported in three cases. Single exon deletions were suspected in 81 cases; further sequencing detected a single nucleotide variant affecting probe hybridization. These cases clustered according to ethnic origin.

Discussion

Population screening for DMD has a significant yield. Most carriers did not report a family history of dystrophinopathies. Screening should be adjusted for methodological limitations. Some cases may require extensive genetic counseling and work‐up.

What's already known about this topic?

Deletions and duplications account for 65%–80% of pathogenic Duchenne muscular dystrophy (DMD) variants.

About two‐thirds of DMD pathogenic variants are inherited from a female carrier.

A nationwide carrier screening for DMD was initiated in Israel in 2020.

What does this study add?

The carrier rate among 12,362 women tested for deletions and duplications in the DMD gene was 1:1374.

Screening should be adjusted for methodological limitations and may require extensive genetic counseling and work‐up.

Muscle histological changes in a large cohort of patients affected with Becker muscular dystrophy

Becker muscular dystrophy (BMD) is a severe X-linked muscle disease. Age of onset, clinical variability, speed of progression and affected tissues display wide variability, making a clinical trial design for drug development very complex. The histopathological changes in skeletal muscle tissue are central to the pathogenesis, but they have not been thoroughly elucidated yet. Here we analysed muscle biopsies from a large cohort of BMD patients, focusing our attention on the histopathological muscle parameters, as fibrosis, fatty replacement, fibre cross sectional area, necrosis, regenerating fibres, splitting fibres, internalized nuclei and dystrophy evaluation. We correlated histological parameters with both demographic features and clinical functional evaluations. The most interesting results of our study are the accurate quantification of fibroadipose tissue replacement and the identification of some histopathological aspects that well correlate with clinical performances. Through correlation analysis, we divided our patients into three clusters with well-defined histological and clinical features. In conclusion, this is the first study that analyses in detail the histological characteristics of muscle biopsies in a large cohort of BMD patients, correlating them to a functional impairment. The collection of these data help to better understand the histopathological progression of the disease and can be useful to validate any pharmacological trial in which the modification of muscle biopsy is utilized as outcome measure.

Overview of gene therapy in spinal muscular atrophy and Duchenne muscular dystrophy

Both 5q-linked spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD) are fatal monogenic neuromuscular disorders caused by loss-of-function mutations. SMA is an autosomal recessive disorder affecting motor neurons that is typically caused by homozygous whole-gene deletions of SMN1. DMD is an X-linked recessive muscle disease most often due to exon deletions, but also duplications and smaller sized variants within the DMD gene. Gene replacement therapy offers the opportunity to correct the underlying genetic defect by the introduction of a functional gene. We review the transformative work from clinical trials to United States Food and Drug Administration approval of onasemnogene abeparvovec-xioi in SMA and its application in clinical practice and the early results of microdystrophin delivery in DMD. We also review the introduction of antisense oligonucleotides to alter pre-messenger RNA splicing to promote exon inclusion (as in nusinersen in SMA) or exclusion (as in eteplirsen in DMD) into neuromuscular therapeutics. There are multiple promising novel genetically mediated therapies on the horizon, which in aggregate point towards a hopeful future for individuals with SMA and DMD.

Essential roles of the dystrophin-glycoprotein complex in different cardiac pathologies

The dystrophin-glycoprotein complex (DGC), situated at the sarcolemma dynamically remodels during cardiac disease. This review examines DGC remodeling as a common denominator in diseases affecting heart function and health. Dystrophin and the DGC serve as broad cytoskeletal integrators that are critical for maintaining stability of muscle membranes. The presence of pathogenic variants in genes encoding proteins of the DGC can cause absence of the protein and/or alterations in other complex members leading to muscular dystrophies. Targeted studies have allowed the individual functions of affected proteins to be defined. The DGC has demonstrated its dynamic function, remodeling under a number of conditions that stress the heart. Beyond genetic causes, pathogenic processes also impinge on the DGC, causing alterations in the abundance of dystrophin and associated proteins during cardiac insult such as ischemia-reperfusion injury, mechanical unloading, and myocarditis. When considering new therapeutic strategies, it is important to assess DGC remodeling as a common factor in various heart diseases. The DGC connects the internal F-actin-based cytoskeleton to laminin-211 of the extracellular space, playing an important role in the transmission of mechanical force to the extracellular matrix. The essential functions of dystrophin and the DGC have been long recognized. DGC based therapeutic approaches have been primarily focused on muscular dystrophies, however it may be a beneficial target in a number of disorders that affect the heart. This review provides an account of what we now know, and discusses how this knowledge can benefit persistent health conditions in the clinic.

Consensus Statement on the Management of Duchenne Muscular Dystrophy in Saudi Arabia During the Coronavirus Disease 2019 Pandemic

Background: The coronavirus disease 2019 (COVID-19) pandemic has caused overwhelming challenges in healthcare worldwide. During such an outbreak, some needs of high-risk groups who require regular follow-ups and long-term management are not met. The vulnerable populations include patients with Duchenne muscular dystrophy (DMD). Duchenne muscular dystrophy is characterized by respiratory complications caused by muscle weakness. Hence, patients with this condition are at high risk of severe diseases including COVID-19. Methods: To standardize care and provide optimal treatment to DMD patients in Saudi Arabia during the COVID-19 pandemic, a panel of experts including neurologists and pediatricians consolidated recommendations for healthcare professionals and caregivers. Results: During this pandemic, substituting unnecessary clinic visits with virtual clinic services was highly recommended, if possible, without compromising clinical outcomes. Duchenne muscular dystrophy patients with respiratory complications should be closely monitored, and those with cardiovascular complications must continue taking angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. Moreover, individualized home-based rehabilitation management was preferred. Glucocorticoid and new gene correction therapies should be continued. However, new gene correction therapy must be post-poned in newly diagnosed patients. A multidisciplinary decision was required before the initiation of hydroxychloroquine based on the COVID-19 treatment protocol. Conclusion: COVID-19 has caused challenges and transformed access to health care. However, these limitations have provided opportunities for the health care system to adapt. Further, telemedicine has become a reliable platform for follow-up appointments that should be conducted by a multidisciplinary team including physicians, dieticians, and physical therapists.

Beneficial effects of one-month sacubitril/valsartan treatment in a patient affected by end-stage dystrophinopathic cardiomyopathy

Dystrophinopathic cardiomyopathy (DCM) is an almost constant manifestation in Becker muscular dystrophy (BMD) patients significantly contributing to morbidity and mortality. The nearly complete replacement of the myocardium by fibrous and fatty connective tissue results in an irreversible cardiac failure, characterized by progressive reduction of the ejection fraction. According to PARADIGM-HF trial results, the European Society of Cardiology (ESC) guidelines recommend the use of sacubitril/valsartan in ambulatory patients with heart failure and reduced ejection fraction, who remain symptomatic despite an optimal medical therapy. To date, little is still known about the use of sacubitril/valsartan in DCM. We report the case of a patient with dystrophinopathic end stage dilated cardiomyopathy with reduced ejection fraction who successfully responded to sacubitril/valsartan treatment.

[A male patient with adult-onset sporadic calpainopathy presenting with hypertrophy of the upper extremities]

A 33-year-old man presented with slowly progressive weakness in the lower extremities over 8 years. At the age of 16 years, the elevation of serum creatine kinase level was detected. Physical examination revealed scapular winging, exaggerated lumbar lordosis and tendoachilles contracture. Gowers sign was positive and proximal dominant limb weakness was noted. Hypertrophy was observed in the upper limbs such as the biceps brachii and forearm flexor muscles. Muscle biopsy showed distinct differences in size of muscle fibers and regenerating and necrotic muscle fibers. A histological study revealed decreased calpain3 expression. Gene analysis of CAPN3 revealed two known gene mutations, leading to a diagnosis of calpainopathy (limb girdle muscular dystrophy 2A; LGMD2A). We here report our patient to discuss findings of upper limb hypertrophy, which are frequently missed compared to the lower limb, but important clinical findings.

Presentation and Management Patterns of Lower Urinary Tract Symptoms in Adults Due to Rare Inherited Neuromuscular Diseases

OBJECTIVE

To describe the urologic sequalae of several rare congenital neuromuscular diseases.

METHODS

We retrospectively reviewed medical records at Gillette Specialty Healthcare (2014-2018) of patients presenting to urology clinic with lower urinary tract symptoms and select rare congenital diseases: muscular dystrophy, spinal muscular atrophy, and Rett syndrome.

RESULTS

Muscular dystrophies (n = 19) are X-linked myogenic disorders characterized by progressive muscle wasting and weakness. Men present to the urologist at variable ages, typically with complaints of functional incontinence and normal cystometrograms; we manage them with oral anticholinergic medications, condom catheter, or suprapubic catheter. Spinal muscular atrophy (n = 6) is a rare autosomal recessive disease characterized by degeneration of the anterior horn cells in the spinal cord and motor nuclei in the lower brainstem leading to progressive muscle weakness and atrophy. Patients typically present with nephrolithiasis and urinary retention in late adolescence/early adulthood, but timing varies. Filling cystometrograms have been normal. We allow passive retention with intermittent catheterization and creation of catheterizable channels, when indicated. Rett syndrome (n = 5) is a rare, noninheritable genetic condition affecting females characterized by a brief period of normal development followed by loss of speech and purposeful hand use; there are characteristic behaviors. Patients present in early adulthood with complaints of urinary retention. We manage retention with permissive retention or sphincter chemodenervation.

CONCLUSION

Several congenital neuromuscular conditions can cause lower urinary tract symptoms when these individuals become adults. We have discussed the clinical characteristics and management of select neurogenic and myogenic bladder conditions seen in adults with congenital conditions.

Genotype-phenotype correlation in Becker muscular dystrophy in Chinese patients

Large deletions and duplications are the most frequent causative mutations in Becker muscular dystrophy (BMD), but genetic profile varied greatly among reports. We performed a comprehensive molecular investigation in 95 Chinese BMD patients. All patients were divided into three subtypes: normal muscle strength (type 1) in 18 cases, quadriceps myopathy (type 2) in 20 cases, and limb-girdle weakness (type 3) in 57 cases. Nineteen cases (20.0%) had small mutations and 76 cases (80.0%) had major rearrangements, including 67 cases (70.5%) of exonic deletions and 9 cases (9.5%) of exonic duplications. We identified 50 cases (65.8%) of in-frame mutations, and 26 cases (34.2%) of frame-shift mutations. The frequency of deletion in exons 13-19 was 30.6% in type 1 patients, 9.7% in type 2 patients, and 10.4% in type 3 patients. The frequency of deletion in exons 45-55 was 28.6% in type 1 patients, 40.8% in type 2, and 50.0% in type 3 patients. All major rearrangements of DMD gene in type 1 patients were also observed in type 3 patients. Our study suggested that frame-shift mutation was not rare in Chinese BMD patients. Although no difference was observed on the forms of DMD gene mutations among the three types of patients, the mutation in proximal region of DMD gene has higher frequency for patients without weakness. Effect of exon skipping for DMD depends on the size and location of the mutation. Additional studies are required to determine whether exon-skipping strategies in proximal region of DMD gene could yield more functional dystrophin.

Cardiac Involvement in Duchenne Muscular Dystrophy and Related Dystrophinopathies

Dystrophinopathies include Duchenne muscular dystrophy (DMD), Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy (XLCM), and facioscapulohumeral muscular dystrophy (FSHD). DMD/BMD are X-linked recessive disorders, related to the synthesis of dystrophin. Most of DMD after the third decade of their age develop cardiomyopathy that remains silent, due to relative physical inactivity. Cardiac disease in female carriers presents with hypertrophy, arrhythmias or dilated cardiomyopathy, clinically overt by increasing age.In ECG, DMD presents increased R/S ratio in the right precordial leads, deep Q waves in the lateral leads, conduction abnormalities, and arrhythmias. Echocardiography, although widely available and inexpensive, is highly depended on the acoustic window and operator's experience. Tissue Doppler can be used to identify early changes of cardiomyopathy and detect progressive cardiac damage. CMR, a noninvasive, nonradiating technique, by evaluation of cardiac volumes, mass, ejection fraction, inflammation, and fibrosis, is ideal for early diagnosis. Subepicardial fibrosis in the inferolateral wall is the typical CMR lesion in DMD/BMD.Early initiation of angiotensin converting enzyme inhibitors (ACEI) treatment, such as perindopril, was associated with lower mortality in DMD with normal LV ejection fraction at study entry. Other studies documented that a beta-blocker (BB), in addition to ACEI, improves LV systolic function in MD. These encouraging results recommend initiation of ACEI and/or BB early after diagnosis of the muscular dystrophy, especially in DMD.

Neuromuscular Disorders and the Role of the Clinical Electrophysiologist

Cardiac involvement is common and may be the presenting or predominant manifestation in a variety of neuromuscular disorders, most notably the inherited muscle disorders, or muscular dystrophies. Cardiac manifestations of the neuromuscular disorders result from pathological involvement of the myocardium and the cardiac conduction system, with resulting cardiomyopathy or rhythm disturbances including supraventricular arrhythmias, life-threatening ventricular arrhythmias, and sudden cardiac death. Many of these neuromuscular disorders are rare and may be unrecognized by even experienced specialists in internal and cardiovascular medicine. Furthermore, the initial cardiac manifestations in these patients are often asymptomatic. The goal of this investigation is to review the scope of cardiac conduction defects and rhythm disturbances in these disorders and to propose some practical recommendations for arrhythmia monitoring and management of these patients.

Dystrophin-Deficient Cardiomyopathy

Dystrophinopathies are a group of distinct neuromuscular diseases that result from mutations in the structural cytoskeletal Dystrophin gene. Dystrophinopathies include Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), X-linked dilated cardiomyopathy, as well as DMD and BMD female carriers. The primary presenting symptom in most dystrophinopathies is skeletal muscle weakness. However, cardiac muscle is also a subtype of striated muscle and is similarly affected in many of the muscular dystrophies. Cardiomyopathies associated with dystrophinopathies are an increasingly recognized manifestation of these neuromuscular disorders and contribute significantly to their morbidity and mortality. Recent studies suggest that these patient populations would benefit from cardiovascular therapies, annual cardiovascular imaging studies, and close follow-up with cardiovascular specialists. Moreover, patients with DMD and BMD who develop end-stage heart failure may benefit from the use of advanced therapies. This review focuses on the pathophysiology, cardiac involvement, and treatment of cardiomyopathy in the dystrophic patient.

Diagnosis of becker muscular dystrophy: Results of Re-analysis of DNA samples

INTRODUCTION

The phenotype of Becker muscular dystrophy (BMD) is highly variable, and the disease may be underdiagnosed. We searched for new mutations in the DMD gene in a cohort of previously undiagnosed patients who had been referred in the period 1985-1995.

METHODS

All requests for DNA analysis of the DMD gene in probands with suspected BMD were re-evaluated. If the phenotype was compatible with BMD, and no deletions or duplications were detected, DNA samples were screened for small mutations.

RESULTS

In 79 of 185 referrals, no mutation was found. Analysis could be performed on 31 DNA samples. Seven different mutations, including 3 novel ones, were found. Long-term clinical follow-up is described.

CONCLUSIONS

Refining DNA analysis in previously undiagnosed cases can identify mutations in the DMD gene and provide genetic diagnosis of BMD. A delayed diagnosis can still be valuable for the proband or the relatives of BMD patients.

The cooperative international neuromuscular research group Duchenne natural history study--a longitudinal investigation in the era of glucocorticoid therapy: design of protocol and the methods used

Contemporary natural history data in Duchenne muscular dystrophy (DMD) is needed to assess care recommendations and aid in planning future trials.

METHODS

The Cooperative International Neuromuscular Research Group (CINRG) DMD Natural History Study (DMD-NHS) enrolled 340 individuals, aged 2-28 years, with DMD in a longitudinal, observational study at 20 centers. Assessments obtained every 3 months for 1 year, at 18 months, and annually thereafter included: clinical history; anthropometrics; goniometry; manual muscle testing; quantitative muscle strength; timed function tests; pulmonary function; and patient-reported outcomes/health-related quality-of-life instruments.

RESULTS

Glucocorticoid (GC) use at baseline was 62% present, 14% past, and 24% GC-naive. In those ≥6 years of age, 16% lost ambulation over the first 12 months (mean age 10.8 years).

CONCLUSIONS

Detailed information on the study methodology of the CINRG DMD-NHS lays the groundwork for future analyses of prospective longitudinal natural history data. These data will assist investigators in designing clinical trials of novel therapeutics.

Pseudometabolic presentation of dystrophinopathy due to a missense mutation

Exercise intolerance with myalgia, muscle stiffness, and recurrent rhabdomyolysis due to mutations in the DMD gene can mimic metabolic myopathies leading to delayed or inaccurate diagnoses. In this retrospective chart review, we report 3 unrelated boys with exertional myalgia, muscle stiffness, myoglobinuria, and normal neurological examination due to an identical point mutation in the DMD gene: a hemizygous T-to-C change in exon 15 (c.1724T>C) resulting in an amino acid substitution of leucine to proline at codon 575. Two of the 3 boys had normal dystrophin immunostaining and Western blot analysis in muscle. This missense mutation has been reported twice before, with at least 1 patient exhibiting rhabdomyolysis. Our report, however, is the first to describe in detail the clinical findings associated with this specific mutation. Further studies and clinical reports are needed to better understand the pathogenicity of the mutation.

Sensitivity of motor unit potential analysis in facioscapulohumeral muscular dystrophy

Template-operated motor unit potential (MUP) analysis has made quantitative electromyography (EMG) feasible, even in busy laboratories, but validation of this approach is still necessary. In the present study, the utility of multi-MUP analysis was assessed in patients with a molecular genetic diagnosis of facioscapulohumeral muscular dystrophy (FSHD). Manual assessment of muscle strength and concentric-needle EMG of the biceps brachii and vastus lateralis muscles were performed. The sensitivity for diagnosing myopathy (mean values and outliers) was tested for eight MUP parameters and four of their combinations. The group comprised 31 patients. Elbow flexion and knee extension strength was normal in 45% and 52% of patients, respectively. The most sensitive MUP parameter was thickness, followed by duration. A combination of three MUP parameters (thickness, amplitude, and duration/area) was needed for maximal sensitivity. The study demonstrated a high sensitivity of multi-MUP analysis in FSHD. Myopathic abnormalities were demonstrated in all weak biceps brachii muscles, and in 77% of biceps brachii muscles with normal strength.

Cognitive impairment in neuromuscular disorders

Several studies have suggested the presence of central nervous system involvement manifesting as cognitive impairment in diseases traditionally confined to the peripheral nervous system. The aim of this review is to highlight the character of clinical, genetic, neurofunctional, cognitive, and psychiatric deficits in neuromuscular disorders. A high correlation between cognitive features and cerebral protein expression or function is evident in Duchenne muscular dystrophy, myotonic dystrophy (Steinert disease), and mitochondrial encephalomyopathies; direct correlation between tissue-specific protein expression and cognitive deficits is still elusive in certain neuromuscular disorders presenting with or without a cerebral abnormality, such as congenital muscular dystrophies, congenital myopathies, amyotrophic lateral sclerosis, adult polyglucosan body disease, and limb-girdle muscular dystrophies. No clear cognitive deficits have been found in spinal muscular atrophy and facioscapulohumeral dystrophy.

Subclinical skeletal muscle abnormalities in patients with hypertrophic cardiomyopathy and their relation to clinical characteristics

BACKGROUND

Some mutations of cardiac sarcomeric proteins causing hypertrophic cardiomyopathy (beta-myosin heavy chain) are associated with skeletal muscle fiber dysfunction, while subclinical skeletal myopathy can be diagnosed by electromyography (EMG) in a substantial proportion of hypertrophic cardiomyopathy patients.

METHODS

In 49 consecutive, unrelated patients with hypertrophic cardiomyopathy, conventional EMG of deltoid, vastus lateralis, tibialis anterior and soleus muscles was performed. No patient had clinically detectable muscle weakness. We compared the clinical and echocardiographic characteristics between patients with normal and patients with myopathic EMG.

RESULTS

Myopathic EMG findings were demonstrated in 13 patients (26.5%), 26 patients (53.1%) had normal findings and 10 patients (20.4%) had indeterminate recordings. There was no significant difference in mean age, maximum wall thickness, left ventricular fraction shortening, NYHA class, the existence of left ventricular outflow tract obstruction, syncope, or the occurrence of nonsustained ventricular tachycardia in the Holter recording among the three groups. Comparison between the myopathic and the normal group revealed that nine patients from the latter (34.6%) had a positive history of sudden death in the family, whereas no patient had such a history in the former group (P=0.015).

CONCLUSION

The higher prevalence of a family history of sudden death in patients with normal EMG, although not thoroughly explained by our data, may reflect differences in the genetic substrate produced by the higher prevalence of high-risk mutations that are not expressed in skeletal muscle (e.g. troponin T). Further evaluation in genotyped patients is warranted.

Pulmonary complications of chronic neuromuscular diseases and their management

Chronic neuromuscular diseases may affect all major respiratory muscles groups including inspiratory, expiratory, and bulbar, and respiratory complications are the major cause of morbidity and mortality. Untreated, many of these diseases lead inexorably to hypercapnic respiratory failure, precipitated in some cases by chronic aspiration and secretion retention or pneumonia, related to impairment of cough and swallowing mechanisms. Many measures are helpful including inhibition of salivation, cough-assist techniques, devices to enhance communication, and physical therapy. In addition, ventilatory assistance is an important part of disease management for patients with advanced neuromuscular disease. Because of its comfort, convenience, and portability advantages, noninvasive positive pressure ventilation (NPPV) has become the modality of first choice for most patients. Patients to receive NPPV should be selected using consensus guidelines, and initiation should be gradual to maximize the chances for success. Attention should be paid to individual preferences for interfaces and early identification of cough impairment that necessitates the use of cough-assist devices. For patients considered unsuitable for noninvasive ventilation, invasive mechanical ventilation should be considered, but only after a frank but compassionate discussion between the patient, family, physician, and other caregivers.

Expression of foetal type acetylcholine receptor is restricted to type 1 muscle fibres in human neuromuscular disorders

In adult muscle, acetylcholine receptors (AChR) are restricted mainly to the motor endplate where the adult isoform (alphabetadeltaepsilon) is expressed. When skeletal muscle is denervated in animal models, there is atrophy of the muscle and a marked increase in expression of the AChR foetal isoform (alphabetagammadelta) containing a gamma-subunit. Similar changes in AChR expression are thought to occur in human muscle. While the role of denervation in regulating AChR gene expression has been widely studied, it has not been determined whether the transcriptional programmes responsible for defining different fibre types have an impact on the expression of AChR genes. We investigated biopsies from patients with a wide spectrum of neuromuscular diseases for expression of the AChR alpha- and gamma-subunits using RNase protection assays, alpha/gamma-duplex reverse transcriptase polymerase chain reaction, immunohistochemistry for foetal AChR and RNA in situ hybridization. Muscle from all patients with neurogenic disorders and, to a lesser extent, myogenic disorders, exhibited markedly increased transcription of the AChR gamma-subunit but, in contrast to previous animal studies, did not show increased AChR alpha-subunit. Moreover, both immunohistochemistry and RNA in situ hybridization revealed that AChR gamma-subunit hyperexpression occurred exclusively in atrophic type 1 and not in atrophic type 2 muscle fibres, irrespective of the underlying neuromuscular disease. We conclude that up-regulation of the AChR gamma-subunit in human muscle disorders is restricted to type 1 muscle fibres and, therefore, that AChR gamma-subunit expression is controlled by a muscle fibre type-restricted transcriptional programme. The factors influencing expression of this and other functional proteins should be relevant to the understanding and treatment of a range of neuromuscular disorders.

X-linked myopathy with excessive autophagy: a clinicopathological study of five new families

In 1988, Kalimo et al. (Ann Neurol 23 (1988) 258)described a new type of X-linked myopathy in a Finnish family. The clinical course was characterized by slow progression of muscle weakness without loss of ambulation in childhood and no evidence of cardiac, respiratory, or central nervous system involvement. Muscle fibers were not necrotic and showed excessive autophagic activity and exocytosis of the phagocytosed material. These authors proposed the name X-linked myopathy with excessive autophagy. Subsequently, only one French family has been reported with similar clinical and histopathological data. We report here five new families with a total of eight affected boys with the same clinical and histopathological features as reported in the original families. Histopathological findings of an asymptomatic mother are also reported. Vacuolar changes in muscle fibers result both from invaginations of the sarcolemma along with a variable component of basal lamina and from an autophagic process. The complement C5b-9 membrane attack complex associated with MHC class 1 antigen and calcium deposits is involved in muscle fiber damage. Among the X-linked myopathies, the identification of this new type is of great interest because of its favorable prognosis and unique morphological findings.

Dilated cardiomyopathy of Becker-type muscular dystrophy with exon 4 deletion--a case report

The authors report a 47-year-old man with Becker-type muscular dystrophy presenting with dilated cardiomyopathy. Left ventriculography showed diffuse severe hypokinesia: left ventricular end-diastolic volume index 193 mL/m2, left ventricular end-systolic volume index 143 mL/m2, and left ventricular ejection fraction 26%. Skeletal muscle biopsy demonstrated a dystrophic process. Genetic analysis revealed a deletion of exon 4. There was a difference in immunostaining pattern between skeletal muscles and cardiac muscles. Severe cardiac dysfunction in this case may be associated with the damage in dystrophin-deficient fibers.

Limb girdle muscular dystrophy: a pathological and immunohistochemical reevaluation

Ninety-seven muscle biopsies from 81 limb girdle muscular dystrophy (LGMD) patients [32 autosomal recessive (AR), 15 autosomal dominant (AD), 34 sporadic] were morphologically reevaluated. Sarcoglycan analysis was done in 37 available muscle biopsies of AR and sporadic patients. Chi-square tests were used to analyze the relation between abnormalities in AR/sporadic versus AD cases. Eighty percent of the muscle biopsies showed a predominantly dystrophic pattern, 20% showed myopathic changes, and 17% of these also had neurogenic changes. Muscle histology was not significantly different between AR/sporadic and AD LGMD; however, the observed abnormalities were more pronounced in the AR/sporadic group. Collections of inflammatory cells were observed in 25% and 10% of the AR/sporadic and AD group, respectively. Sarcoglycanopathy was diagnosed in 25% of the AR and sporadic patients of the 37 families tested. We conclude that the histological picture of AR/sporadic and AD LGMD is essentially the same, and sarcoglycanopathy constitutes an important part of the AR/sporadic patients.

Dystrophinopathies

The discovery of the subsarcolemmal muscle fiber protein dystrophin has, to a certain extent, replaced former nosological terms of Duchenne (DMD) and Becker (BMD) muscular dystrophies by the term dystrophinopathies. The immunohistochemical and Western blot analysis of dystrophin has not only enlarged the clinical spectrum of dystrophinopathies, but has also made carrier detection of DMD more reliable, particularly in manifesting carriers without family history. Moreover, prenatal muscle biopsy, under selected circumstances, can show presence or absence of dystrophin, ie, in the latter case an affected male fetus. Molecular genetics have provided a wealth of genetic details in the dystrophinopathies, but therapy has not yet succeeded to a similar extent, on the contrary, myoblast transplantation has not resulted in any clinical improvement.

Dystrophinopathy in two young boys with exercise-induced cramps and myoglobinuria

Two young boys were referred for evaluation of metabolic myopathy because of elevated serum levels of creatine kinase, cramps and pigmenturia. Immunohistochemical studies of dystrophin in muscle biopsies showed reduced intensity of the stain with a patchy and discontinuous pattern in most fibers. In both patients dystrophin was undetectable by immunoblotting. DNA analysis of the dystrophin gene was not informative in one patient; in the other it revealed an in-frame deletion comprising exons 3-6. These observations suggest that the two patients are affected with an unusual phenotype of Becker muscular dystrophy. Dystrophin analysis should be included in the evaluation of patients with childhood-onset of recurrent myoglobinuria.

Asymptomatic Becker muscular dystrophy: histological changes in biopsied muscles

The histological changes observed in consecutive tests of biopsied muscles from an asymptomatic patient with Becker muscular dystrophy (BMD) are reported. The first biopsy showed active muscle necrosis and clustered regenerating fibers. The second biopsy revealed chronic myopathic changes mixed with neurogenic involvement. It is stressed that active myogenic changes observed in younger and asymptomatic BMD patients were followed by chronic myogenic or neurogenic change with age. Finally, we confirm the necessity of checking for dystrophin of abnormal size or reduced abundance by immunoblot analysis.

The clinical, genetic and dystrophin characteristics of Becker muscular dystrophy. I. Natural history

We have investigated 67 patients with proven Becker muscular dystrophy (BMD) using a standard protocol including a detailed history and a functional and clinical examination. Our aim was to define the natural history of the disease in a large cohort of patients in the light of the diagnostic methods now available. In all patients with or without an X-linked family history, the diagnosis was confirmed by the identification of a deletion or other abnormality in the dystrophin gene, and abnormal dystrophin on immunoblotting and immunocytochemistry of muscle biopsy samples. In graphs of functional and muscle score against age, two groups of patients emerged. In the larger group the disease was milder and patients remained ambulant into their forties or beyond. A smaller group had more severe disease with a slightly earlier onset, much earlier loss of ambulation, more frequent abnormal electrocardiographic findings and much lower reproductive fitness. The relationship of these clinical findings to the genetic and protein abnormalities found in the patients is explored in the accompanying paper.

A case of myopathy associated with a dystrophin gene deletion and abnormal glycogen storage

A 30-year-old man with no family history of muscle disease presented with a progressive proximal myopathy and calf hypertrophy characteristic of Becker muscular dystrophy. A deletion of exons 45 to 48 in the dystrophin gene was confirmed by Southern blotting and multiplex polymerase chain reaction. However, muscle biopsy showed massive accumulation of glycogen, although no significant abnormality of glycolytic pathway enzymes could be demonstrated. This patient therefore has a previously undescribed myopathy associated with both Becker muscular dystrophy and a glycogen storage disorder of unknown aetiology.

[Early differentiation between Duchenne and Becker muscular dystrophy: clinical, laboratory, electrophysiology, histochemical, and immunohistochemical study of 138 cases]

194 clinical, laboratory, electrophysiologic, histological, histochemical and immunohistochemical parameters were studied through statistical analysis in 112 cases of Duchenne muscular dystrophy (DMD) and in 26 cases of Becker muscular dystrophy (BMD). It was found a significant statistical difference (p < 0.05) between the two groups concerning the age of evaluation, beginning of symptoms, difficulty in walking, running, climbing and going downstairs, frequent falling down, support to walk, localized muscle pain, stopping climb stairs, and inability to walk. Muscle biopsy showed statistically significant (p < 0.05) differences between the two groups regarding the intensity of connective tissue and focal adipose tissue proliferation, presence of diffuse rounded atrophic and angulated fibers, diffuse hypertrophic and splitting fibers. There were also differences regarding excessive internal fibers nuclei, hypertrophic types 1 and 2 fibers, angulated atrophic fibers and focal increasing in the NADH-TR, angulated atrophic fibers in non-specific esterase, and accumulated NBT in the periphery of fibers in succinic dehidrogenase. Isolatedly muscle biopsy gave the correct diagnosis in 52.7% of DMD cases and in 69.2% of BMD cases. Dystrophin detection by immunofluorescence (60 cases) showed: absence in 87.0% of fibers in DMD cases, and sarcolemmal membrane discontinuites in all BMD cases. The muscle biopsy diagnosis had an agreement with the dystrophin results in 82.6% of DMD cases and 71.4% of BMD cases.

Delayed expression of dystrophin on regenerating muscle from two siblings with Becker muscular dystrophy

We present here a unique expression of dystrophin on biopsied muscle from 2 siblings with Becker muscular dystrophy (BMD). They had neither muscle weakness nor atrophy. Clustered dystrophin-deficient fibers were constituted to regenerating basophilic fibers (mainly type 2C fiber) based on histochemical stainings. We speculate that the developmental delay in the expression of dystrophin is a characteristic finding in regenerating fibers from asymptomatic and young BMD patients, such as the siblings in this report.

The heart in Becker muscular dystrophy, facioscapulohumeral dystrophy, and Bethlem myopathy

We report a study, assessing involvement of the heart in 33 familial cases of Becker muscular dystrophy (BMD), 31 familiar cases of facioscapulohumeral (FSH) dystrophy, and 27 familial cases of Bethlem myopathy. In the patients with BMD, correlations of myocardial involvement with age and extent of musculoskeletal involvement were made. We performed physical examination, chest x-ray, electrocardiographic (EKG), and echocardiographic examination on all patients, and continuous EKG Holter-monitoring in the patients with FSH dystrophy. Thirteen patients with BMD (45%) showed EKG changes similar to those found in Duchenne muscular dystrophy. Only 1 of the 13 individuals with cardiac involvement was wheelchair-bound. We found no evidence of cardiac changes in the patients with FSH dystrophy. In Bethlem myopathy, only 1 patient had a form of hypertrophic cardiomyopathy (asymmetrical septal hypertrophy).

Two distinct mutations in a single dystrophin gene: chance occurrence or premutation?

We report on a kindred segregating 2 distinct mutations of a dystrophin gene. DNA analysis showed that the second mutation, a deletion, arose in the same gene carrying the primary defect which produced a Becker phenotype in the affected males. The DNA data for this family are reported and the alternative explanations of chance occurrence and premutation are discussed to explain these unusual findings.

Muscle histology in Becker muscular dystrophy

Twenty patients with Becker muscular dystrophy (BMD), confirmed by dystrophin tests, were studied histologically. There were several morphological differences between younger (less than or equal to 15-year-old) and older (greater than 15-year-old) patients. In the younger patients, active muscle fiber necrosis followed by a regenerating process was conspicuous. In the older patients, the active degenerative changes appeared less prominent and, instead, more chronic myopathic changes such as moth-eaten fibers, fiber splitting, and hypertrophic fibers were evident. These age-dependent differences in the pathology of BMD were irrespective of the duration of clinical symptoms, i.e., BMD patients of a similar age showed a similar morphological feature regardless of age at onset. Although the presence of mild fiber type grouping and some small angulated atrophic fibers suggested a certain degree of neurogenic involvement, none of biopsies showed significant grouped atrophy as seen in neuropathic disorders. There was no correlation between the histological changes and the specific dystrophin abnormality.

Becker muscular dystrophy or spinal muscular atrophy?--Dystrophin studies resolve conflicting results of electromyography and muscle biopsy

We studied a 29-year-old man with slowly progressive proximal leg weakness, calf hypertrophy, and high serum levels of creatine kinase activity. Clinically, it was not possible to identify his as a sporadic instance of Becker muscular dystrophy (BMD) or one of spinal muscular atrophy. The problem arose because electromyography and elevated creatine kinase suggested a myopathy whereas changes in the muscle biopsy resembled a neurogenic disorder. The diagnosis of BMD was made by DNA analysis which detected a deletion at Xp21 and by immunoelectrophoresis and immunohistochemical tests that identified an abnormal form of gene product, dystrophin. These studies were important for genetic counselling, identifying an X-linked disease instead of one that is autosomal recessive.

[Dystrophin in the differentiation between Duchenne and Becker muscular dystrophies: an immunohistochemical study compared with clinical stage, serum enzymes and muscle biopsy]

Study of 55 cases of progressive muscular dystrophies (34 Duchenne, 12 Duchenne with residual dystrophin and 9 Becker patients) comparing age, age at the initial symptoms, duration of symptoms, levels of serum enzymes, degree of disability measured by the Vignos and Archibald scale, and the type and amount of dystrophin found in the muscle biopsies by immunofluorescence. Statistical analysis showed a tendency of the symptoms and progression of disease to be related with the low quantity of dystrophin in the biopsies. There was no difference in the parameter analysed between the Duchenne patients with and without residual dystrophin, as well as the Duchenne with residual dystrophin and Becker patients. There was an inverse relation with the amount of dystrophin and the endomysial connective tissue and fatty infiltration, and a direct relation with hypertrophic fibers and atrophic angulated fibers in the NADH-tetrazolium reductase. In the comments a discussion is made about the difficulties in differentiate Duchenne and Becker dystrophies, the cases with residual dystrophin and the importance of the correct diagnosis.

Heterogeneity of dystrophin expression in patients with Duchenne and Becker muscular dystrophy

This report documents the results of an integrated biochemical and immunocytochemical investigation into the expression of dystrophin (the protein product of the Duchenne muscular dystrophy gene) in muscle biopsies from 226 patients. It is the first study in which dystrophin has been analysed on blots and on tissue sections in such a large number of patients using the same (monoclonal) antibody. The 140 patients with Xp21 muscular dystrophy who were included in this study represent a continuous spectrum of disease severity and this range was reflected in the heterogeneity of dystrophin expression which was observed with respect to abundance, size and the pattern of tissue localisation. Approximately 40% of biopsies obtained from patients diagnosed as having Duchenne muscular dystrophy (DMD) contained isolated clearly positive fibres and a further 20% had very weak labelling on a large number of fibres. Biopsies from patients with Becker muscular dystrophy (BMD) showed labelling patterns which varied from weak labelling on the majority of fibres to clear labelling on all fibres. Typically, however, there was inter- and intra-fibre variation in labelling intensity. Approximately 85% of the 52 BMD and 54 DMD patients who had unequivocal labelling on blots demonstrated a protein of abnormal size. The remaining 15% had a protein of normal size but reduced abundance. Overall, the estimated abundance of dystrophin correlated well with clinical assessments of the disease severity expressed in patients. We conclude that dystrophin analysis is an essential and dependable technique for the differential diagnosis of patients with Xp21 muscular dystrophy.

An unusual variant of Becker muscular dystrophy

We report on 5 brothers with slowly progressive limbgirdle weakness. Calf hypertrophy was absent. The levels of creatine kinase, electromyography, and findings from a muscle biopsy specimen were compatible with muscular dystrophy. The propositus's biopsy specimen also showed numerous rimmed vacuoles. DNA analysis revealed a deletion in the dystrophin gene, establishing a diagnosis of Becker muscular dystrophy. Both the absence of calf hypertrophy and the presence of rimmed vacuoles are unusual features in this disorder.

Differentiation of Becker muscular dystrophy from limb-girdle muscular dystrophy and Kugelberg-Welander disease using a cDNA probe

A 31-year-old man previously investigated for a neuromuscular disorder was diagnosed as having either limb-girdle dystrophy, spinal muscular atrophy, or Becker muscular dystrophy. Extensive clinical and special neurological investigations failed to clarify this differential diagnosis. However, recent DNA studies have shown a deletion of the dystrophin gene, thereby providing an unequivocal diagnosis of Becker muscular dystrophy. The application of molecular genetic techniques in the diagnosis of inherited neuromuscular disorders is discussed.