EFNS guideline on diagnosis and management of limb girdle muscular dystrophies

Psychosocial resources and psychopathology among persons with neuromuscular disorders during the COVID-19 pandemic

BACKGROUND

The COVID-19 pandemic substantially affected the lives of persons with inherited neuromuscular disorders (INMD), causing disruption in clinical and support services. While several studies have investigated mental health, distress and psychosocial resources in the general population during the pandemic, little is known about the experience of persons with INMD.

METHODS

This study was aimed to fill this gap by jointly investigating both psychopathological symptoms and psychosocial resources - specifically, resilience and perceived social support - among persons with INMD during the pandemic, taking into account demographic and clinical factors. Between April and December 2020, 59 participants with INMD (aged 15-59, 71.2% M) completed a questionnaire collecting demographic and clinical data, the Multidimensional Scale of Perceived Social Support, the Resilience Scale for Adults, and the Achenbach System of Empirically Based Assessment.

RESULTS

Overall, participants showed good levels of resilience and perceived social support. A minority of participants reported clinically relevant psychopathological symptoms, 28.81% for anxiety and depression. Most psychopathological symptoms were negatively correlated with resilience (-0.347 < r < - .420), but not significantly associated with social support. Consistent with previous studies, regression analyses highlighted that participants with Duchenne muscular dystrophy were more prone to report anxious and depressive symptoms (B = 1.748, p = .028, OR = 5.744), and participants with myotonic dystrophy, attention problems (B = 2.339, p = .006, OR = 10.376). Resilience emerged as a potential predictor of lower anxious-depressive symptoms (B=-1.264, p = .012, OR = 0.283).

CONCLUSIONS

The findings suggest the importance to investigate psychosocial resources in addition to psychopathology among persons with INMD, and to design interventions supporting resilience as a protective factor for mental health promotion.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

Sarcoglycanopathies: an update

Sarcoglycanopathies are the most severe forms of autosomal recessive limb-girdle muscular dystrophies (LGMDs), constituting about 10-25% of LGMDs. The clinical phenotype is variable, but onset is usually in the first decade of life. Patients present muscle hypertrophy, elevated CK, variable muscle weaknesses, and progressive loss of ambulation. Four subtypes are known: LGMDR3, LGMDR4, LGMDR5 and LGMDR6, caused, respectively, by mutations in the SGCA, SGCB,SGCG and SGCD genes. Their four coded proteins, α-SG, ß-SG, λ-SG and δ-SG are part of the dystrophin-glycoprotein complex (DGC) present in muscle sarcolemma, which acts as a linker between the cytoskeleton of the muscle fiber and the extracellular matrix, providing mechanical support to the sarcolemma during myofiber contraction. Many different mutations have already been identified in all the sarcoglycan genes, with a predominance of some mutations in different populations. The diagnosis is currently based on the molecular screening for these mutations. Therapeutic approaches include the strategy of gene replacement mediated by a vector derived from adeno-associated virus (AAV). Pre-clinical studies have shown detectable levels of SG proteins in the muscle, and some improvement in the phenotype, in animal models. Therapeutic trials in humans are ongoing.

Assessment of Nocturnal Hypoventilation by Different Methods and Definitions in Children with Neuromuscular Disease: Oxycapnography and Blood Gas Analysis

Objective

To investigate whether partial arterial carbon dioxide pressure (PaCO₂) level in arterial blood gas analysis that was used to predict nocturnal hypoventilation (NH) is concordant with nocturnal end-tidal CO₂ (PetCO₂) measurement obtained by a noninvasive method of oxycapnography in children with neuromuscular disease (NMD).

Methods

Twenty-one patients aged 6-18 years with a confirmed diagnosis of NMD were enrolled. Each patient underwent a nocturnal oxycapnography study using an orinasal probe and a pulse oximetry finger probe to record PetCO₂, oxygen saturation (SpO₂), pulse rate, and respiratory rate. Arterial blood gas analysis was performed to record PaCO₂ levels on three occasions at night (23:00 pm, 03:00 am, 07:00 am).

Results

The mean overnight PaCO₂ level of the three blood gas analyses (mean PaCO₂noct) was 41.78±4.69 mmHg. A significant change was observed between mean PaCO₂ 23:00 and PaCO₂ 07:00 levels (p=0.032). There was no significant difference between PaCO₂, PetCO₂, and SpO₂ levels in the NMD group. The interclass correlation coefficient between PaCO₂ 07:00 and PetCO₂ levels was 0.791 (95% CI: 0.533-0.923); the interclass correlation coefficient between overnight mean PaCO₂ and PetCO₂ levels was 0.811 (95% CI:0.533-0.923).

Conclusion

Our study indicates that nocturnal PetCO₂ and PaCO₂ levels were statistically comparable but the use of PaCO₂ alone is not adequate to make an early diagnosis of NH in NMD. There is a need for making more restrictive definitions for NH, and conducting studies with larger study populations to reach an agreement on the best definition of hypoventilation, and updating consensus guidelines.

Use of RNA‑sequencing to detect abnormal transcription of the collagen α‑2 (VI) chain gene that can lead to Bethlem myopathy

Bethlem myopathy (BM) is an autosomal dominant or autosomal recessive disorder and is usually associated with mutations in the collagen VI genes. In the present study, the pathogenicity of a novel splice-site mutation was explored using RNA-sequencing in a family with suspected BM, and a myopathy panel was performed in the proband. The genetic status of all family members was confirmed using Sanger sequencing. Clinical data and magnetic resonance imaging (MRI) features were also documented. In silico analysis was performed to predict the effects of the splice mutation. RNA-sequencing and reverse transcription (RT)-PCR were used to assess aberrant splicing. Immunocytochemistry was conducted to measure collagen VI protein levels within the gastrocnemius and in cultured skin fibroblasts. The results revealed that three patients in the family shared a similar classic BM presentation. MRI revealed distinct patterns of fatty infiltration in the lower extremities. A novel splicing mutation c.736-1G>C in the collagen α-2 (VI) chain (COL6A2) gene was found in all three patients. In silico analysis predicted that the mutation would destroy the normal splice acceptor site. RNA-sequencing detected two abnormal splicing variants adjacent to the mutation site, and RT-PCR confirmed the RNA-sequencing findings. Furthermore, a defect in the collagen protein within cultured fibroblasts was detected using immunocytochemistry. The mutation c.736-1G>C in the COL6A2 gene caused aberrant splicing and led to premature termination of protein translation. In conclusion, these findings may improve our knowledge of mutations of the COL6A2 gene associated with BM and demonstrated that RNA-sequencing can be a powerful tool for finding the underlying mechanism of a disease-causing mutations at a splice site.

A Wearable Device for Breathing Frequency Monitoring: A Pilot Study on Patients with Muscular Dystrophy

Patients at risk of developing respiratory dysfunctions, such as patients with severe forms of muscular dystrophy, need a careful respiratory assessment, and periodic follow-up visits to monitor the progression of the disease. In these patients, at-home continuous monitoring of respiratory activity patterns could provide additional understanding about disease progression, allowing prompt clinical intervention. The core aim of the present study is thus to investigate the feasibility of using an innovative wearable device for respiratory monitoring, particularly breathing frequency variation assessment, in patients with muscular dystrophy. A comparison of measurements of breathing frequency with gold standard methods showed that the device based on the inertial measurement units (IMU-based device) provided optimal results in terms of accuracy errors, correlation, and agreement. Participants positively evaluated the device for ease of use, comfort, usability, and wearability. Moreover, preliminary results confirmed that breathing frequency is a valuable breathing parameter to monitor, at the clinic and at home, because it strongly correlates with the main indexes of respiratory function.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

As a group, the limb-girdle muscular dystrophies (LGMDs) are the fourth most prevalent genetic muscle disease, yet they are still not well known or understood. This article defines and describes LGMDs, delineates a diagnostic strategy, and discusses treatment of the LGMDs.

RECENT FINDINGS

In 2018, the definition of the LGMDs was further refined, and a new nomenclature was proposed. Diagnosis of the LGMDs was long guided by the distinctive clinical characteristics of each particular subtype but now integrates use of genetics-with next-generation sequencing panels, exomes, and full genome analysis-early in the diagnostic assessment. Appreciation of the phenotypic diversity of each LGMD subtype continues to expand. This emphasizes the need for precision genetic diagnostics to better understand each subtype and formulate appropriate management for individual patients. Of significant relevance, the explosion of research into therapeutic options accentuates the need for accurate diagnosis, comprehensive disease characterization, and description of the natural histories of the LGMDs to move the field forward and to mitigate disease impact on patients with LGMD.

SUMMARY

The LGMDs are genetic muscle diseases that superficially appear similar to one another but have important differences in rates of progression and concomitant comorbidities. Definitive diagnoses are crucial to guide management and treatment now and in the future. As targeted treatments emerge, it will be important for clinicians to understand the nomenclature, diagnosis, clinical manifestations, and treatments of the LGMDs.

Displaced Myonuclei in Cancer Cachexia Suggest Altered Innervation

An idiopathic myopathy characterized by central nuclei in muscle fibers, a hallmark of muscle regeneration, has been observed in cancer patients. In cancer cachexia skeletal muscle is incapable of regeneration, consequently, this observation remains unaccounted for. In C26-tumor bearing, cachectic mice, we observed muscle fibers with central nuclei in the absence of molecular markers of bona fide regeneration. These clustered, non-peripheral nuclei were present in NCAM-expressing muscle fibers. Since NCAM expression is upregulated in denervated myofibers, we searched for additional makers of denervation, including AchRs, MUSK, and HDAC. This last one being also consistently upregulated in cachectic muscles, correlated with an increase of central myonuclei. This held true in the musculature of patients suffering from gastrointestinal cancer, where a progressive increase in the number of central myonuclei was observed in weight stable and in cachectic patients, compared to healthy subjects. Based on all of the above, the presence of central myonuclei in cancer patients and animal models of cachexia is consistent with motor neuron loss or NMJ perturbation and could underlie a previously neglected phenomenon of denervation, rather than representing myofiber damage and regeneration in cachexia. Similarly to aging, denervation-dependent myofiber atrophy could contribute to muscle wasting in cancer cachexia.

Comprehensive Assessment of Cardiac Involvement in Muscular Dystrophies by Cardiac MR Imaging

Muscular dystrophy is a group of genetically inherited diseases with irreversible and progressive muscle loss and is associated with cardiac involvement. Particularly in Duchenne and Becker dystrophies, cardiac disorders are the leading causes of mortality. Cardiovascular magnetic resonance imaging (CMR) can detect even incipient myocardial fibrosis (late gadolinium enhancement), which has prognostic significance in patients with preserved left ventricular function by echocardiogram and before the onset of symptoms. Early detection of cardiac abnormalities by CMR enables early cardioprotective treatment, leading to a better prognosis.

Cross-sectional study into age-related pathology of mouse models for limb girdle muscular dystrophy types 2D and 2F

Limb girdle muscular dystrophy (LGMD) types 2D and 2F are caused by mutations in the genes encoding for α- and δ-sarcoglycan, respectively, leading to progressive muscle weakness. Mouse models exist for LGMD2D (Sgca-/-) and 2F (Sgcd-/-). In a previous natural history study, we described the pathology in these mice at 34 weeks of age. However, the development of muscle pathology at younger ages has not been fully characterised yet. We therefore performed a study into age-related changes in muscle function and pathology by examining mice at different ages. From 4 weeks of age onwards, male mice were subjected to functional tests and sacrificed at respectively 8, 16 or 24 weeks of age. Muscle histopathology and expression of genes involved in muscle pathology were analysed for several skeletal muscles, while miRNA levels were assessed in serum. In addition, for Sgcd-/- mice heart pathology was assessed. Muscle function showed a gradual decline in both Sgca-/- and Sgcd-/- mice. Respiratory function was also impaired at all examined timepoints. Already at 8 weeks of age, muscle pathology was prominent, and fibrotic, inflammatory and regenerative markers were elevated, which remained relatively constant with age. In addition, Sgcd-/- mice showed signs of cardiomyopathy from 16 weeks of age onwards. These results indicate that Sgca-/- and Sgcd-/- are relevant disease models for LGMD2D and 2F.

Cardiomyopathy in Children: Classification and Diagnosis: A Scientific Statement From the American Heart Association

In this scientific statement from the American Heart Association, experts in the field of cardiomyopathy (heart muscle disease) in children address 2 issues: the most current understanding of the causes of cardiomyopathy in children and the optimal approaches to diagnosis cardiomyopathy in children. Cardiomyopathies result in some of the worst pediatric cardiology outcomes; nearly 40% of children who present with symptomatic cardiomyopathy undergo a heart transplantation or die within the first 2 years after diagnosis. The percentage of children with cardiomyopathy who underwent a heart transplantation has not declined over the past 10 years, and cardiomyopathy remains the leading cause of transplantation for children >1 year of age. Studies from the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry have shown that causes are established in very few children with cardiomyopathy, yet genetic causes are likely to be present in most. The incidence of pediatric cardiomyopathy is ≈1 per 100 000 children. This is comparable to the incidence of such childhood cancers as lymphoma, Wilms tumor, and neuroblastoma. However, the published research and scientific conferences focused on pediatric cardiomyopathy are sparcer than for those cancers. The aim of the statement is to focus on the diagnosis and classification of cardiomyopathy. We anticipate that this report will help shape the future research priorities in this set of diseases to achieve earlier diagnosis, improved clinical outcomes, and better quality of life for these children and their families.

Demembranated skeletal and cardiac fibers produce less force with altered cross-bridge kinetics in a mouse model for limb-girdle muscular dystrophy 2i

Limb-girdle muscular dystrophy 2i (LGMD2i) is a dystroglycanopathy that compromises myofiber integrity and primarily reduces power output in limb muscles but can influence cardiac muscle as well. Previous studies of LGMD2i made use of a transgenic mouse model in which a proline-to-leucine (P448L) mutation in fukutin-related protein severely reduces glycosylation of α-dystroglycan. Muscle function is compromised in P448L mice in a manner similar to human patients with LGMD2i. In situ studies reported lower maximal twitch force and depressed force-velocity curves in medial gastrocnemius (MG) muscles from male P448L mice. Here, we measured Ca²⁺-activated force generation and cross-bridge kinetics in both demembranated MG fibers and papillary muscle strips from P448L mice. Maximal activated tension was 37% lower in MG fibers and 18% lower in papillary strips from P448L mice than controls. We also found slightly faster rates of cross-bridge recruitment and detachment in MG fibers from P448L than control mice. These increases in skeletal cross-bridge cycling could reduce the unitary force output from individual cross bridges by lowering the ratio of time spent in a force-bearing state to total cycle time. This suggests that the decreased force production in LGMD2i may be due (at least in part) to altered cross-bridge kinetics. This finding is notable, as the majority of studies germane to muscular dystrophies have focused on sarcolemma or whole muscle properties, whereas our findings suggest that the disease pathology is also influenced by potential downstream effects on cross-bridge behavior.

(-)-Epicatechin inhibits development of dilated cardiomyopathy in δ sarcoglycan null mouse

BACKGROUND AND AIMS

Several studies propose that (-)-epicatechin, a flavonol present in high concentration in the cocoa, has cardioprotective effects. This study aimed to evaluate the impact of (-)-epicatechin on the development of dilated cardiomyopathy in a δ sarcoglycan null mouse model.

METHODS AND RESULTS

δ Sarcoglycan null mice were treated for 15 days with (-)-epicatechin. Histological and morphometric analysis of the hearts treated mutant mice showed significant reduction of the vasoconstrictions in the coronary arteries as well as fewer areas with fibrosis and a reduction in the loss of the ventricular wall. On the contrary, it was observed a thickening of this region. By Western blot analysis, it was shown, and increment in the phosphorylation level of eNOS and PI3K/AKT/mTOR/p70S6K proteins in the heart of the (-)-epicatechin treated animals. On the other hand, we observed a significantly decreased level of the atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) heart failure markers.

CONCLUSION

All the results indicate that (-)-epicatechin has the potential to prevent the development of dilated cardiomyopathy of genetic origin and encourages the use of this flavonol as a pharmacological therapy for dilated cardiomyopathy and heart failure diseases.

A novel mutation in the DYSF gene in a patient with a presumed inflammatory myopathy

Dysferlinopathy, a progressive muscular dystrophy, results from mutations in the Dysferlin gene (DYSF, MIM*603009). Traditional diagnosis relies on the reduction or absence of dysferlin. However, altered dysferlin has been observed in other myopathies, leading to a precise diagnosis through molecular genetics. In this study, we report a patient who was previously misdiagnosed as inflammatory myopathy based on routine clinicopathological examinations alone. However, muscle biopsy specimens were analyzed further by immunohistochemistry of muscular dystrophy-related proteins, and gene-targeted next generation sequencing (NGS) was used to correctly identify muscular dystrophy. DNA was sequenced with NGS and the detected mutation was verified by Sanger sequencing. Our targeted NGS found a novel missense mutation (c.5392G > A) in the DYSF gene, allowing correct diagnosis of LGMD2B in our patient. We discovered of a novel missense mutation in the DYSF gene and have broadened the DYSF mutation spectrum, which may be correlated in patients with presumed dysferlinopathy, especially when lymphocytic infiltration is observed.

Perceptions of the transition from receiving the diagnosis recessive limb-girdle muscular dystrophy to becoming in need of human support and using a wheelchair: an interview study

Purpose: To describe perceptions of the transition from receiving the diagnosis recessive limb-girdle muscular dystrophy to becoming in need of human support to manage daily life and using a wheelchair for ambulation, from the affected young adults' and their parents' perspectives. Method: A qualitative and descriptive study design was used. Semi-structured interviews were held with 14 young adults diagnosed with recessive limb-girdle muscular dystrophy and 19 parents. Phenomenography was used for data analysis. Results: The diagnosis was described as being a shock and difficult to comprehend but also as a relief and a tool for information. Beginning to use a wheelchair was perceived to be mentally difficult but it also provided freedom. New ways of living involved physical, emotional, practical, and social difficulties as well as experiences of learning to adapt to the disease. The transition was overshadowed by concern about disease progression and influenced by facilitating factors, which were young adult being seen as a person; supportive family and friends; mobilized internal resources; meaningful daily activities; adapted environment; and professional support. Conclusions: The different perceptions expressed in this study highlight the importance of identifying personal perceptions and needs in order to optimize support provided by healthcare professionals. Implications for Rehabilitation The different perceptions described in this study emphasize the need for person-centered care for young adults living with recessive limb-girdle muscular dystrophy and their parents. Regular controls and professional support to cope with the disease and its consequences should be offered, not only at the time of diagnosis but also throughout disease progression. Beginning to use a wheelchair can be a psychologically distressing process, which has to be acknowledged by healthcare professionals when introducing it. Healthcare professionals should not only recognize the importance of having social relations and activities that are meaningful but also be a link to authorities in society and to interest organizations that can help to facilitate the person's management of the disease.

Association of Limb-Girdle muscular dystrophy with multiple sclerosis: A case report

Background:

The association of limb-girdle muscular dystrophy (LGMD) with other neurological disorders is uncommon.

Case presentation:

We report a 25-year-old female with LGMD who suffered from slowly progressive proximal muscular weakness and atrophy since she was 12 years of age. The patient recently presented with acute loss of left side visual acuity. After evaluation, findings were suggestive of multiple sclerosis.

Conclusions:

This is the first report of LGMD in association with MS. The simultaneous occurrence of MS with myopathies may be incidental but there may be a genetic susceptibility for both diseases. This comorbidity may influence the treatment of MS.

Mutational spectrum of Chinese LGMD patients by targeted next-generation sequencing

This study aimed to study the diagnostic value of targeted next-generation sequencing (NGS) in limb-girdle muscular dystrophies (LGMDs), and investigate the mutational spectrum of Chinese LGMD patients. We performed targeted NGS covering 420 genes in 180 patients who were consecutively suspected of LGMDs and underwent muscle biopsies from January 2013 to May 2015. The association between genotype and myopathological profiles was analyzed in the genetically confirmed LGMD patients. With targeted NGS, one or more rare variants were detected in 138 patients, of whom 113 had causative mutations, 10 sporadic patients had one pathogenic heterozygous mutation related to a recessive pattern of LGMDs, and 15 had variants of uncertain significance. No disease-causing mutation was found in the remaining 42 patients. Combined with the myopathological findings, we achieved a positive genetic diagnostic rate as 68.3% (123/180). Totally 105 patients were diagnosed as LGMDs with genetic basis. Among these 105 patients, the most common subtypes were LGMD2B in 52 (49.5%), LGMD2A in 26 (24.8%) and LGMD 2D in eight (7.6%), followed by LGMD1B in seven (6.7%), LGMD1E in four (3.8%), LGMD2I in three (2.9%), and LGMD2E, 2F, 2H, 2K, 2L in one patient (1.0%), respectively. Although some characteristic pathological changes may suggest certain LGMD subtypes, both heterogeneous findings in a certain subtype and overlapping presentations among different subtypes were not uncommon. The application of NGS, together with thorough clinical and myopathological evaluation, can substantially improve the molecular diagnostic rate in LGMDs. Confirming the genetic diagnosis in LGMD patients can help improve our understanding of their myopathological changes.

Epidemiological and Molecular Characterization of a Mexican Population Isolate with High Prevalence of Limb-Girdle Muscular Dystrophy Type 2A Due to a Novel Calpain-3 Mutation

Limb-Girdle Muscular Dystrophy type 2 (LGMD2) is a group of autosomally recessive inherited disorders defined by weakness and wasting of the shoulder and pelvic girdle muscles. In the past, several population isolates with high incidence of LGMD2 arising from founder mutation effects have been identified. The aim of this work is to describe the results of clinical, epidemiologic, and molecular studies performed in a Mexican village segregating numerous cases of LGMD2. A population census was conducted in the village to identify all LGMD affected patients. Molecular analysis included genome wide homozygosity mapping using a 250K SNP Affymetrix microarray followed by PCR amplification and direct nucleotide sequencing of the candidate gene. In addition, DNA from 401 randomly selected unaffected villagers was analyzed to establish the carrier frequency of the LGMD2 causal mutation. A total of 32 LGMD2 patients were identified in the village, rendering a disease prevalence of 4.3 (CI: 2.9–5.9) cases per 1,000 habitants (1 in 232). Genome wide homozygosity mapping revealed that affected individuals shared a 6.6 Mb region of homozygosity at chromosome 15q15. The identified homozygous interval contained CAPN3, the gene responsible for LGMD2 type A (LGMD2A). Direct sequencing of this gene revealed homozygosity for a novel c.348C>A mutation (p.Ala116Asp) in DNA from all 20 affected subjects available for genetic screening, except one which was heterozygous for the mutation. In such patient, a heterozygous c.2362AG>TCATCT deletion/insertion was recognized as the second CAPN3 mutation. Western blot and autocatalytic activity analyses in protein lysates from skeletal muscle biopsy obtained from a p.Ala116Asp homozygous patient suggested that this particular mutation increased the autocatalytic activity of CAPN3. Thirty eigth heterozygotes of the p.Ala116Asp mutation were identified among 401 genotyped unaffected villagers, yielding a population carrier frequency of 1 in 11. This study demonstrates that a cluster of patients with LGMD2A in a small Mexican village arises from a novel CAPN3 founder mutation. Evidence of allelic heterogeneity is demonstrated by the recognition of an additional CAPN3 mutation in a single affected. Our study provides an additional example of genetic isolation causing a high prevalence of LGMD and of successful molecular characterization of the disease by means of homozygosity mapping. The identification of a very high carrier frequency of the LGMD2-causing mutation has implications for more rational genetic counseling in this community.

Cardiopulmonary dysfunction in patients with limb-girdle muscular dystrophy 2A

Introduction: Little is known about the frequency of cardiopulmonary failure in limb‐girdle muscular dystrophy type 2A (calpainopathy) patients, although some studies have reported severe cardiomyopathy or respiratory failure. Methods: To clarify the frequency of cardiopulmonary dysfunction in this patient population, we retrospectively reviewed the respiratory and cardiac function of 43 patients with calpainopathy. Results: Nine of the 43 patients had forced vital capacity (FVC) < 80%, and 3 used noninvasive positive pressure ventilation. Mean FVC was significantly lower in patients who were nonambulant and had normal creatine kinase levels. Only 1 patient had a prolonged QRS complex duration. Echocardiography revealed that 1 patient had very mild left ventricular dysfunction. Conclusions: These findings suggest that patients with calpainopathy may develop severe respiratory failure, but cardiac dysfunction is infrequent. Muscle Nerve55: 465–469, 2017

The italian limb girdle muscular dystrophy registry: Relative frequency, clinical features, and differential diagnosis

INTRODUCTION

Limb girdle muscular dystrophies (LGMDs) are characterized by high molecular heterogeneity, clinical overlap, and a paucity of specific biomarkers. Their molecular definition is fundamental for prognostic and therapeutic purposes.

METHODS

We created an Italian LGMD registry that included 370 molecularly defined patients. We reviewed detailed retrospective and prospective data and compared each LGMD subtype for differential diagnosis purposes.

RESULTS

LGMD types 2A and 2B are the most frequent forms in Italy. The ages at disease onset, clinical progression, and cardiac and respiratory involvement can vary greatly between each LGMD subtype. In a set of extensively studied patients, targeted next-generation sequencing (NGS) identified mutations in 36.5% of cases.

CONCLUSION

Detailed clinical characterization combined with muscle tissue analysis is fundamental to guide differential diagnosis and to address molecular tests. NGS is useful for diagnosing forms without specific biomarkers, although, at least in our study cohort, several LGMD disease mechanisms remain to be identified. Muscle Nerve 55: 55-68, 2017.

Where do we stand in trial readiness for autosomal recessive limb girdle muscular dystrophies?

Autosomal recessive limb girdle muscular dystrophies (LGMD2) are a group of genetically heterogeneous diseases that are typically characterised by progressive weakness and wasting of the shoulder and pelvic girdle muscles. Many of the more than 20 different conditions show overlapping clinical features with other forms of muscular dystrophy, congenital, myofibrillar or even distal myopathies and also with acquired muscle diseases. Although individually extremely rare, all types of LGMD2 together form an important differential diagnostic group among neuromuscular diseases. Despite improved diagnostics and pathomechanistic insight, a curative therapy is currently lacking for any of these diseases. Medical care consists of the symptomatic treatment of complications, aiming to improve life expectancy and quality of life. Besides well characterised pre-clinical tools like animal models and cell culture assays, the determinants of successful drug development programmes for rare diseases include a good understanding of the phenotype and natural history of the disease, the existence of clinically relevant outcome measures, guidance on care standards, up to date patient registries, and, ideally, biomarkers that can help assess disease severity or drug response. Strong patient organisations driving research and successful partnerships between academia, advocacy, industry and regulatory authorities can also help accelerate the elaboration of clinical trials. All these determinants constitute aspects of translational research efforts and influence patient access to therapies. Here we review the current status of determinants of successful drug development programmes for LGMD2, and the challenges of translating promising therapeutic strategies into effective and accessible treatments for patients.

An overview of muscle diseases presenting in adulthood

Patients with muscle disease present not only to neurologists, but also to rheumatologists and general physicians. This article provides a framework of how to approach patients with suspected muscle disease, and reviews the clinical features of the most frequently encountered acquired and genetic conditions in adult practice.

Nocturnal hypoventilation in neuromuscular disease: prevalence according to different definitions issued from the literature

PURPOSE

Restrictive respiratory failure is a major cause of morbidity and mortality in neuromuscular diseases (NMD). Home mechanical ventilation (HMV) is used to treat hypoventilation, identified by daytime hypercapnia or nocturnal desaturation. Recently, transcutaneous measure of CO2 (TcCO2) has been increasingly used to detect hypoventilation, using different cut-offs. We aimed to compare the prevalence of hypoventilation in an unselected adult NMD population according to different definitions issued from the literature.

METHODS

All consecutive nocturnal capno-oximetries performed between 2010 and 2014 in unventilated adult NMD patients were analysed retrospectively. Concomitant blood gas analysis and lung function data were collected. Patients on oxygen therapy were excluded. Hypoventilation was defined according to eight criteria, based on daytime PaCO2, daytime base excess, nocturnal SpO2 or TcCO2.

RESULTS

Data from 232 patients were analysed (mean age 43.1 ± 15.4 years; 50.0 % women; vital capacity 59.2 ± 24.2 % of predicted). The hypoventilation prevalence was 10.3 to 61.2 %, depending on the used definition. The different definitions showed 49.1 to 94.8 % concordance (Cohen's kappa for agreement 0.115 to 0.763). Overall agreement between the eight definitions was poor (Light's kappa 0.267), and agreement between definitions based on nocturnal SpO2 and those based on TcCO2 was even lower (Light's kappa 0.204).

CONCLUSIONS

We found large differences in hypoventilation prevalence according to the used definition. This has practical consequences, as HMV indication relies upon hypoventilation detection. We believe that capno-oximetry should be included in the diagnostic tools used to detect hypoventilation but this requires an update of consensus guidelines to agree upon the best definition.

Common recessive limb girdle muscular dystrophies differential diagnosis: why and how?

Limb girdle muscular dystrophies are heterogeneous autosomal hereditary neuromuscular disorders. They produce dystrophic changes on muscle biopsy and they are associated with mutations in several genes involved in muscular structure and function. Detailed clinical, laboratorial, imaging, diagnostic flowchart, photographs, tables, and illustrated diagrams are presented for the differential diagnosis of common autosomal recessive limb girdle muscular dystrophy subtypes diagnosed nowadays at one reference center in Brazil. Preoperative image studies guide muscle biopsy site selection. Muscle involvement image pattern differs depending on the limb girdle muscular dystrophy subtype. Muscle involvement is conspicuous at the posterior thigh in calpainopathy and fukutin-related proteinopathy; anterior thigh in sarcoglycanopathy; whole thigh in dysferlinopathy, and telethoninopathy. The precise differential diagnosis of limb girdle muscular dystrophies is important for genetic counseling, prognostic orientation, cardiac and respiratory management. Besides that, it may probably, in the future, provide specific genetic therapies for each subtype.

Young adults' experiences of living with recessive limb-girdle muscular dystrophy from a salutogenic orientation: an interview study

PURPOSE

To describe young adults' experiences of living with recessive limb-girdle muscular dystrophy (LGMD2) from a salutogenic orientation.

METHODS

A qualitative explorative interview study, including 14 participants aged 20-30 years, was performed focusing on comprehensibility, manageability and meaningfulness in daily life. Content analysis was used for data analysis.

RESULT

Living with LGMD2 not only implies learning to live with the disease and the variations between good and bad periods but also means trying to make sense of a progressive disease that brings uncertainty about future health, by striving to make the best of the situation. Disease progression involves practical and mental struggle, trying to maintain control over one's life despite vanished physical functions that require continual adjustments to the body. Restrictions in a double sense were described, not only due to the disease but also due to poor comprehension of the disease in society. Lack of knowledge about LGMD2 among professionals often results in having to fight for the support needed.

CONCLUSION

In order to manage daily life, it is important to be seen and understood as an individual in contacts with professionals and in society in general, to have informal social support and meaningful activities as well as access to personal assistance if necessary.

IMPLICATIONS FOR REHABILITATION

Recessive limb-girdle muscular dystrophy (LGMD2) is a group of progressive disorders, which manifest in physical and psychological consequences for the individual. According to the salutogenic orientation, people need to find life comprehensible, manageable and meaningful, i.e. to achieve a sense of coherence (SOC), but living with LGMD2 may recurrently challenge the individual's SOC. Through the holistic view of the individual's situation that the salutogenic orientation provides, professionals may support the individual to strengthen SOC and thereby facilitate the movement towards health.

Molecular Genetic Diagnosis of a Bethlem Myopathy Family with an Autosomal-Dominant COL6A1 Mutation, as Evidenced by Exome Sequencing

Background

We describe herein the application of whole exome sequencing (WES) for the molecular genetic diagnosis of a large Korean family with dominantly inherited myopathy.

Case Report

The affected individuals presented with slowly progressive proximal weakness and ankle contracture. They were initially diagnosed with limb-girdle muscular dystrophy (LGMD) based on clinical and pathologic features. However, WES and subsequent capillary sequencing identified a pathogenic splicing-site mutation (c.1056+1G>A) in COL6A1, which was previously reported to be an underlying cause of Bethlem myopathy. After identification of the genetic cause of the disease, careful neurologic examination revealed subtle contracture of the interphalangeal joint in the affected members, which is a characteristic sign of Bethlem myopathy. Therefore, we revised the original diagnosis from LGMD to Bethlem myopathy.

Conclusions

This is the first report of identification of COL6A1-mediated Bethlem myopathy in Korea, and indicates the utility of WES for the diagnosis of muscular dystrophy.

Finding the sweet spot: assembly and glycosylation of the dystrophin-associated glycoprotein complex

The dystrophin-associated glycoprotein complex (DGC) is a collection of glycoproteins that are essential for the normal function of striated muscle and many other tissues. Recent genetic studies have implicated the components of this complex in over a dozen forms of muscular dystrophy. Furthermore, disruption of the DGC has been implicated in many forms of acquired disease. This review aims to summarize the current state of knowledge regarding the processing and assembly of dystrophin-associated proteins with a focus primarily on the dystroglycan heterodimer and the sarcoglycan complex. These proteins form the transmembrane portion of the DGC and undergo a complex multi-step processing with proteolytic cleavage, differential assembly, and both N- and O-glycosylation. The enzymes responsible for this processing and a model describing the sequence and subcellular localization of these events are discussed.

Limb-girdle muscular dystrophies: where next after six decades from the first proposal (Review)

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of disorders, which has led to certain investigators disputing its rationality. The mutual feature of LGMD is limb-girdle affection. Magnetic resonance imaging (MRI), perioral skin biopsies, blood-based assays, reverse-protein arrays, proteomic analyses, gene chips and next generation sequencing are the leading diagnostic techniques for LGMD and gene, cell and pharmaceutical treatments are the mainstay therapies for these genetic disorders. Recently, more highlights have been shed on disease biomarkers to follow up disease progression and to monitor therapeutic responsiveness in future trials. In this study, we review LGMD from a variety of aspects, paying specific attention to newly evolving research, with the purpose of bringing this information into the clinical setting to aid the development of novel therapeutic strategies for this hereditary disease. In conclusion, substantial progress in our ability to diagnose and treat LGMD has been made in recent decades, however enhancing our understanding of the detailed pathophysiology of LGMD may enhance our ability to improve disease outcome in subsequent years.

Total intravenous anesthesia for aortic aneurysm replacement surgery in a patient with limb-girdle dystrophy

We report the anesthetic management with total intravenous anesthesia of a 61-year-old male diagnosed with limb-girdle muscular dystrophy admitted for replacement of ascending aorta due to an aortic aneurysm. Limb-girdle muscular dystrophy belongs to a genetically heterogeneous group of muscular dystrophies involving shoulder and hip girdles. Although the risk of malignant hyperthermia does not seem to be increased in these patients compared with the general population, the exposure to inhaled anesthetics and succinylcholine should probably be avoided because these patients have a predisposition to hyperkalemia and rhabdomyolysis. We chose to use total intravenous anesthesia with propofol, remifentanil and muscle relaxants to reduce oxygen consumption, and later to reduce the doses of propofol and remifentanil. The combination of a carefully planned anesthetic strategy, anesthetic depth, and neuromuscular blockade monitoring is explained.

A family with 2 different hereditary diseases leading to early cardiac involvement

Autosomal dominant limb-girdle muscular dystrophy type 1B (LGMD 1B) is caused by mutations in the LMNA gene. The disorder is associated with potentially fatal cardiac arrhythmias. Brugada syndrome (BS) is an autosomal dominant channelopathy linked to mutations in the SCN5A gene. BS is also associated with increased risk of sudden cardiac death. We reported a family in which a novel gene mutation, a missense mutation (c.80C>T) in exon 1 of the LMNA gene causing autosomal dominant LGMD 1B, occurred in association with SCN5A gene mutation causing BS. After the diagnosis of BS, 4 patients received implantable cardioverter-defibrillator therapy. Eight members of the family deceased at early age before the diagnosis. We emphasized the co-occurrence of 2 different conditions predisposing to sudden cardiac death: LGMD 1B caused by a novel mutation and BS.

Undiagnosed genetic muscle disease in the north of England: an in depth phenotype analysis

Advances in the molecular characterisation of genetic muscle disease has been rapid, as demonstrated by a recent analysis of these conditions in the north of England by Norwood et al (2009), in which a genetic diagnosis was achieved for 75.7% of patients. However, there remain many patients with suspected genetic muscle disease in who a diagnosis is not obtained, often despite considerable diagnostic effort, and these patients are now being considered for the application of new technologies such as next generation sequencing. This study aimed to provide an in-depth phenotype analysis of undiagnosed patients referred to the Northern region muscle clinic with suspected genetic muscle disease, with the intention of gaining insight into these conditions, identifing cases with a shared phenotype who may be amenable to collective diagnostic testing or research, and evaluating the strengths and limitations of our current diagnostic strategy. We used two approaches: a review of clinical findings in patients with undiagnosed muscle disease, and a hierarchical cluster analysis to provide an unbiased interpretation of the phenotype data. These joint approaches identified a correlation of phenotypic features according to the age of disease onset and also delineated several interesting groups of patients, as well as highlighting areas of frequent diagnostic difficulty that could benefit from the use of new high-throughput diagnostic techniques. Correspondence to: anna.sarkozy@ncl.ac.uk

Ancestral founder mutations in calpain-3 in the Indian Agarwal community: historical, clinical, and molecular perspective

INTRODUCTION

Clinical heterogeneity of limb-girdle muscular dystrophies (LGMDs, 24 known subtypes), which includes overlapping phenotypes and varying ages of onset and morbidity, adds complexity to clinical and molecular diagnoses.

METHODS

To diagnose LGMD subtype, protein analysis, using immunohistochemistry (IHC) and immunoblotting, was followed by gene sequencing through a panel approach (simultaneous sequencing of known LGMD genes) in 9 patients from unrelated families of the Indian Agarwal community. Haplotype studies were performed by targeted SNP genotyping to establish mutation segregation.

RESULTS

We identified 2 founder mutations in CAPN3, a missense (c.2338G>C; p.D780H) and a splice-site (c.2099-1G>T) mutation, on 2 different haplotype backgrounds. The patients were either heterozygous for both or homozygous for either of these mutations.

CONCLUSIONS

Founder mutations have immediate clinical application, at least in selected population groups. Clinically available gene panels may provide a definitive molecular diagnosis for heterogeneous disorders such as LGMD.

Gender-specific differences in major cardiac events and mortality in lamin A/C mutation carriers

AIMS

Mutations in the lamin A/C gene (LMNA) cause a variety of clinical phenotypes, including dilated cardiomyopathy. LMNA is one of the most prevalent mutated genes in dilated cardiomyopathy, and is associated with a high risk of arrhythmias, sudden cardiac death, and heart failure. There are few data on the impact of age and gender on cardiac disease penetrance and mortality.

METHODS AND RESULTS

In a multicentre cohort of 269 LMNA mutation carriers, we evaluated gender-specific penetrance of cardiac involvement and major cardiac events. All-cause mortality of mutation carriers [standardized mortality ratio (SMR)] was determined. Cardiac disease penetrance was age dependent and almost complete at the age of 70 years. The presence of an LVEF ≤45% was significantly higher in men (P < 0.001). However, there was no difference between genders in the prevalence of atrioventricular block, atrial tachyarrhythmias, and non-sustained ventricular tachycardia. Malignant ventricular arrhythmias (26% vs. 8%) and end-stage heart failure (28% vs. 14%) were more common in men than in women (P < 0.001 and P = 0.006, respectively). All-cause mortality of mutation carriers was significantly increased [SMR 4.0, 95% confidence interval (CI) 2.8-5.2] between the ages of 15 and 75 years. Mortality in men was higher than in women (hazard ratio 2.2, 95% CI 1.2-4.3).

CONCLUSIONS

This large cohort of LMNA mutation carriers demonstrates a high cardiac disease penetrance and a high mortality in mutation carriers. Male mutation carriers have a worse prognosis due to a higher prevalence of malignant ventricular arrhythmias and end-stage heart failure.

An analysis of exome sequencing for diagnostic testing of the genes associated with muscle disease and spastic paraplegia

In this study, we assess exome sequencing (ES) as a diagnostic alternative for genetically heterogeneous disorders. Because ES readily identified a previously reported homozygous mutation in the CAPN3 gene for an individual with an undiagnosed limb girdle muscular dystrophy, we evaluated ES as a generalizable clinical diagnostic tool by assessing the targeting efficiency and sequencing coverage of 88 genes associated with muscle disease (MD) and spastic paraplegia (SPG). We used three exome-capture kits on 125 individuals. Exons constituting each gene were defined using the UCSC and CCDS databases. The three exome-capture kits targeted 47-92% of bases within the UCSC-defined exons and 97-99% of bases within the CCDS-defined exons. An average of 61.2-99.5% and 19.1-99.5% of targeted bases per gene were sequenced to 20X coverage within the CCDS-defined MD and SPG coding exons, respectively. Greater than 95-99% of targeted known mutation positions were sequenced to ≥1X coverage and 55-87% to ≥20X coverage in every exome. We conclude, therefore, that ES is a rapid and efficient first-tier method to screen for mutations, particularly within the CCDS annotated exons, although its application requires disclosure of the extent of coverage for each targeted gene and supplementation with second-tier Sanger sequencing for full coverage.

Childhood onset of limb-girdle muscular dystrophy

Limb-girdle muscular dystrophies comprise a rare heterogeneous group of genetic muscular dystrophies, involving 15 autosomal recessive subtypes and seven autosomal dominant subtypes. Autosomal recessive dystrophy is far more common than autosomal dominant dystrophy. Typical clinical features include progressive limb muscle weakness and atrophy (proximal greater than distal), varying from very mild to severe. Significant overlap of clinical phenotypes, with genetic and clinical heterogeneity, constitutes the rule for this group of diseases. Muscle biopsies are useful for histopathologic and immunolabeling studies, and DNA analysis is the gold standard to establish the specific form of muscular dystrophy. A definitive diagnosis among various subtypes is challenging, and the data presented here provide neuromuscular clinicians with additional information to help attain that goal.

Distinct pathophysiological mechanisms of cardiomyopathy in hearts lacking dystrophin or the sarcoglycan complex

Duchenne muscular dystrophy (DMD) and limb girdle muscular dystrophy (LGMD) 2C-F result from the loss of dystrophin and the sarcoglycans, respectively. Dystrophin, a cytoskeletal protein, is closely associated with the membrane-bound sarcoglycan complex. Despite this tight biochemical association, the function of dystrophin and the sarcoglycan subunits may differ. The loss of dystrophin in skeletal muscle results in muscle that is highly susceptible to contraction-induced damage, but the skeletal muscle of mice lacking γ- or δ-sarcoglycan are less susceptible. Using mouse models of DMD, LGMD-2C, and LGMD-2F, we demonstrate that isolated cardiac myocytes from mice lacking either γ- or δ-sarcoglycan have normal compliance. In contrast, dystrophin-deficient myocytes display poor passive compliance and are susceptible to terminal contracture following mild passive extensions. Mice deficient in dystrophin and, less so, δ-sarcoglycan have reduced survival during in vivo dobutamine stress testing compared to controls. Catheter-based hemodynamic studies show deficits in both baseline and dobutamine-stimulated cardiac function in all of the dystrophic mice compared to control mice, with dystrophin-deficient mice having the poorest function. In contrast, histopathology showed increased fibrosis in the sarcoglycan-deficient hearts, but not in hearts lacking dystrophin. In summary, this study provides important insights into the unique mechanisms of disease underlying these different models of inherited dystrophic cardiomyopathy and supports a model where dystrophin, but not the sarcoglycans, protects the cardiac myocyte against mechanical damage.

Muscular dystrophies and neurologic diseases that present as myopathy

Chronic muscle weakness is a common complaint among patients seen in rheumatology and neuromuscular specialty clinics. This article focuses on adult-onset muscular dystrophies, select hereditary myopathies, and other neuromuscular conditions that must be distinguished from acquired causes of inflammatory muscle disease such as polymyositis. A few organizing principles help to focus the evaluation and narrow the differential diagnosis.

Limb-girdle muscular dystrophy 2A

Limb-girdle muscular dystrophy type 2A (LGMD2A) is caused by mutations in the gene CAPN3 located in the chromosome region 15q15.1-q21.1. To date more than 300 mutations have been described. This gene encodes for a 94-kDa nonlysosomal calcium-dependent cysteine protease and its function in skeletal muscle is not fully understood. It seems that calpain-3 has an unusual zymogenic activation that involves, among other substrates, cytoskeletal proteins. Calpain-3 is thought to interact with titin and dysferlin. Calpain-3 deficiency produces abnormal sarcomeres that lead eventually to muscle fiber death. Hip adductors and gluteus maximus are the earliest clinically affected muscles. No clinical differences have been reported depending on the type of mutation in the CAPN3 gene. The muscle biopsy shows variability of fiber size, interstitial fibrosis, internal nuclei, lobulated fibers, and, in some cases, presence of eosinophils. Recent gene expression profiling studies have shown upregulation of interleukin-32 and immunoglobulin genes, which may explain the eosinophilic infiltration. Two mouse knockout models of CAPN3 have been characterized. There are no curative treatments for this disease. However, experimental therapeutics using mouse models conclude that adeno-associated virus (AAV) vectors seem to be one of the best approaches because of their efficiency and persistency of gene transfer.