Cognitive profile and MRI findings in limb-girdle muscular dystrophy 2I

Cognitive abnormalities in Becker muscular dystrophy: a mysterious link between dystrophin deficiency and executive functions

BACKGROUND

Distrophinopathies are a heterogeneous group of neuromuscular disorders due to mutations in the DMD gene. Different isoforms of dystrophin are also expressed in the cerebral cortex and Purkinje cells. Despite cognitive abnormalities in Duchenne muscular dystrophy subjects that have been described in the literature, little is known about a comprehensive cognitive profile in Becker muscular dystrophy patients.

AIM

The aim of this study was to assess cognitive functioning in Becker muscular dystrophy patients by using an extensive neuropsychological battery. Our hypothesis is that the most impaired functions are the highly intentional and conscious ones, such as working memory functions, which require a prolonged state of cellular activation.

METHODS

We performed an extensive neuropsychological assessment on 28 Becker muscular dystrophy patients from 18 to 65 years old. As control subjects, we selected 20 patients with limb-girdle muscular dystrophy, whose clinical picture was similar except for cognitive integrity. The evaluation, although extended to all areas, was focused on prefrontal control skills, with a distinction between inhibitory processes of selective attention and activating processes of working memory.

RESULTS AND CONCLUSIONS

Significant underperformances were found exclusively in the Dual Task and PASAT tests, to demonstrate a selective impairment of working memory that, while not causing intellectual disability, reduces the intellectual potential of patients with Becker muscular dystrophy.

Dysferlinopathy in Tunisia: clinical spectrum, genetic background and prognostic profile

Dysferlinopathy is a rare group of hereditary muscular dystrophy with an autosomal recessive mode of inheritance caused by a mutation in the DYSF gene. It encodes for the dysferlin protein, which has a crucial role in multiple cellular processes, including muscle fiber membrane repair. This deficit has heterogeneous clinical presentations. In this study, we collected 20 Tunisian patients with a sex ratio of 1 and a median age of 50.5 years old (Interquartile range (IQR) = [36,5-54,75]). They were followed for periods ranging from 5 to 48 years. The median age at onset was 17 years old (IQR = [16,8-28,4]). Five major phenotypes were identified: Limb-girdle muscular dystrophy (LGMDR2) (35%), a proximodistal phenotype (35%), Miyoshi myopathy (10%),  Distal myopathy with anterior tibial onset (DMAT) (10%), and asymptomatic HyperCKemia (10%). At the last evaluation, more than half of patients (55%) were on wheelchair. Loss of ambulation occurred generally during the fourth decade. After 20 years of disease progression, two patients with a proximodistal phenotype (10%) developed dilated cardiomyopathy and mitral valve regurgitation. Restrictive respiratory syndrome was observed in three patients (DMAT: 1 patient, proximodistal phenotype: 1 patient, LGMDR2: 1 patient). Genetic study disclosed five mutations. We observed clinical heterogeneity between families and even within the same family. Disease progression was mainly slow to intermediate regardless of the phenotype.

Ribitol dose-dependently enhances matriglycan expression and improves muscle function with prolonged life span in limb girdle muscular dystrophy 2I mouse model

Limb Girdle Muscular Dystrophy 2I (LGMDR9) is one of the most common LGMD characterized by defects in glycosylation of α-dystroglycan (matriglycan) resulting from mutations of Fukutin-related protein (FKRP). There is no effective therapy currently available. We recently demonstrated that ribitol supplement increases levels of matriglycan in cells in vitro and in FKRP-P448L (P448L) mutant mouse model through drinking water administration. To be clinically relevant, we have now conducted a dose-escalating efficacy study by gavage in P448L mutant mice. Six months of ribitol treatment daily significantly rescued functions of skeletal, respiratory, and cardiac muscles dose-dependently. This was associated with a dose dependent increase in matriglycan and improvement in muscle pathology with reductions in muscle degeneration, inflammatory infiltration and fibrosis. Importantly, ribitol significantly increased life span and muscle functions of the female animals receiving treatment from 10 months of age. The only observed side effect was gastrointestinal tract bloating with loose stool and this effect is also dose dependent. The results validate the mechanism that ribitol as a pre-substrate of glycosyltransferase is able to compensate for the decreased function of mutant FKRP with restoration of matriglycan expression and provide a guidance for future clinical trial design.

Phenotype and Genotype Study of Chinese POMT2-Related α-Dystroglycanopathy

Objective

Alpha-dystroglycanopathy (α-DGP) is a subtype of muscular dystrophy caused by defects in the posttranslational glycosylation of α-dystroglycan (α-DG). Our study aimed to summarize the clinical and genetic features of POMT2-related α-DGP in a cohort of patients in China.

Methods

Pedigrees, clinical data, and laboratory tests of patients diagnosed with POMT2-related α-DGP were analyzed retrospectively. The pathogenicity of variants in POMT2 were predicted by bioinformatics software. The variants with uncertain significance were verified by further analysis.

Results

The 11 patients, comprising eight males and three females, were from nine non-consanguineous families. They exhibited different degrees of muscle weakness, ambulation, and intellectual impairment. Among them, three had a muscle-eye-brain disease (MEB)-like phenotype, five presented congenital muscular dystrophy with intellectual disability (CMD-ID), and three presented limb-girdle muscular dystrophy (LGMD). Overall, nine novel variants of POMT2, including two non-sense, one frameshift and six missense variants, were identified. The pathogenicity of two missense variants, c.1891G > C and c.874G > C, was uncertain based on bioinformatics software prediction. In vitro minigene analysis showed that c.1891G > C affects the splicing of POMT2. Immunofluorescence staining with the IIH6C4 antibody of muscle biopsy from the patient carrying the c.874G > C variant showed an apparent lack of expression.

Conclusion

This study summarizes the clinical and genetic characteristics of a cohort of POMT2-related α-DGP patients in China for the first time, expanding the mutational spectrum of the disease. Further study of the pathogenicity of some missense variants based on enzyme activity detection is needed.

MiRNAs, Myostatin, and Muscle MRI Imaging as Biomarkers of Clinical Features in Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is an X-linked recessive disorder caused by dystrophin gene mutations. The phenotype and evolution of this muscle disorder are extremely clinical variable. In the last years, circulating biomarkers have acquired remarkable importance in their use as noninvasive biological indicators of prognosis and in monitoring muscle disease progression, especially when associated to muscle MRI imaging. We investigated the levels of circulating microRNAs (myo-miRNAs and inflammatory miRNAs) and of the proteins follistatin (FSTN) and myostatin (GDF-8) and compared results with clinical and radiological imaging data. In eight BMD patients, including two cases with evolving lower extremity weakness treated with deflazacort, we evaluated the expression level of 4 myo-miRNAs (miR-1, miR-206, miR-133a, and miR-133b), 3 inflammatory miRNAs (miR-146b, miR-155, and miR-221), FSTN, and GDF-8 proteins. In the two treated cases, there was pronounced posterior thigh and leg fibrofatty replacement assessed by muscle MRI by Mercuri score. The muscle-specific miR-206 was increased in all patients, and inflammatory miR-221 and miR-146b were variably elevated. A significant difference in myostatin expression was observed between steroid-treated and untreated patients. This study suggests that microRNAs and myostatin protein levels could be used to better understand the progression and management of the disease.

Towards Central Nervous System Involvement in Adults with Hereditary Myopathies

There is increasing evidence of central nervous system involvement in numerous neuromuscular disorders primarily considered diseases of skeletal muscle. Our knowledge on cerebral affection in myopathies is expanding continuously due to a better understanding of the genetic background and underlying pathophysiological mechanisms. Intriguingly, there is a remarkable overlap of brain pathology in muscular diseases with pathomechanisms involved in neurodegenerative or neurodevelopmental disorders. A rapid progress in advanced neuroimaging techniques results in further detailed insight into structural and functional cerebral abnormalities. The spectrum of clinical manifestations is broad and includes movement disorders, neurovascular complications, paroxysmal neurological symptoms like migraine and epileptic seizures, but also behavioural abnormalities and cognitive dysfunction. Cerebral involvement implies a high socio-economic and personal burden in adult patients sometimes exceeding the everyday challenges associated with muscle weakness. It is especially important to clarify the nature and natural history of brain affection against the background of upcoming specific treatment regimen in hereditary myopathies that should address the brain as a secondary target. This review aims to highlight the character and extent of central nervous system involvement in patients with hereditary myopathies manifesting in adulthood, however also includes some childhood-onset diseases with brain abnormalities that transfer into adult neurological care.

The roles of dystroglycan in the nervous system: insights from animal models of muscular dystrophy

Dystroglycan is a cell membrane protein that binds to the extracellular matrix in a variety of mammalian tissues. The α-subunit of dystroglycan (αDG) is heavily glycosylated, including a special O-mannosyl glycoepitope, relying upon this unique glycosylation to bind its matrix ligands. A distinct group of muscular dystrophies results from specific hypoglycosylation of αDG, and they are frequently associated with central nervous system involvement, ranging from profound brain malformation to intellectual disability without evident morphological defects. There is an expanding literature addressing the function of αDG in the nervous system, with recent reports demonstrating important roles in brain development and in the maintenance of neuronal synapses. Much of these data are derived from an increasingly rich array of experimental animal models. This Review aims to synthesize the information from such diverse models, formulating an up-to-date understanding about the various functions of αDG in neurons and glia of the central and peripheral nervous systems. Where possible, we integrate these data with our knowledge of the human disorders to promote translation from basic mechanistic findings to clinical therapies that take the neural phenotypes into account.

Summary: Dystroglycan is a ubiquitous matrix receptor linked to brain and muscle disease. Unraveling the functions of this protein will inform basic and translational research on neural development and muscular dystrophies.

An update on diagnostic options and considerations in limb-girdle dystrophies

INTRODUCTION

Limb-girdle muscular dystrophies (LGMDs) encompass a clinically heterogeneous group of rare, genetic progressive muscle disorders presenting with weakness and atrophy of predominant pelvic and shoulder muscles. The spectrum of disease severity ranges from severe childhood-onset muscular dystrophy to adult-onset dystrophy. Areas covered: The review presents an update of the clinical phenotypes and diagnostic options for LGMD including both dominant and recessive LGMD and consider their differential clinical and histopathological features. An overview of most common phenotypes and of possible complications is given. The management of the main clinical respiratory, cardiac, and central nervous system complications are covered. The instrumental, muscle imaging, and laboratory exams to assess and reach diagnosis are described. The use of recent genetic techniques such as next generation sequencing (NGS), whole-exome sequencing compared to other techniques (e.g. DNA sequencing, protein analysis) is covered. Currently available drugs or gene therapy and rehabilitation management are focused on. Expert commentary: Many LGMD cases, which for a long time previously remained without a molecular diagnosis, can now be investigated by NGS. Gene mutation analysis is always required to obtain a certain molecular diagnosis, fundamental to select homogeneous group of patients for future pharmaceutical and gene trials.

Limb girdle muscular dystrophy due to mutations in POMT2

BACKGROUND

Mutations in the gene coding for protein O-mannosyl-transferase 2 (POMT2) are known to cause severe congenital muscular dystrophy, and recently, mutations in POMT2 have also been linked to a milder limb-girdle muscular dystrophy (LGMD) phenotype, named LGMD type 2N (LGMD2N). Only four cases have been reported so far.ClinicalTrials.gov ID: NCT02759302 METHODS: We report 12 new cases of LGMD2N, aged 18-63 years. Muscle involvement was assessed by MRI, muscle strength testing and muscle biopsy analysis. Other clinical features were also recorded.

RESULTS

Presenting symptoms were difficulties in walking, pain during exercise, delayed motor milestones and learning disabilities at school. All had some degree of cognitive impairment. Brain MRIs were abnormal in 3 of 10 patients, showing ventricular enlargement in one, periventricular hyperintensities in another and frontal atrophy of the left hemisphere in a third patient. Most affected muscle groups were hip and knee flexors and extensors on strength testing. On MRI, most affected muscles were hamstrings followed by paraspinal and gluteal muscles. The 12 patients in our cohort carried 11 alleles with known mutations, whereas 11 novel mutations accounted for the remaining 13 alleles.

CONCLUSION

We describe the first cohort of patients with LGMD2N and show that unlike other LGMD types, all patients had cognitive impairment. Primary muscle involvement was found in hamstring, paraspinal and gluteal muscles on MRI, which correlated well with reduced muscle strength in hip and knee flexors and extensors. The study expands the mutational spectrum for LGMD2N, with the description of 11 novel POMT2 mutations in the association with LGMD2N.

CLINICAL TRIAL REGISTRATION

NCT02759302.

Next-Generation Sequencing to Diagnose Muscular Dystrophy, Rhabdomyolysis, and HyperCKemia

Background:Neuromuscular disorders are a phenotypically and genotypically diverse group of diseases that can be difficult to diagnose accurately because of overlapping clinical features and nonspecific muscle pathology. Next-generation sequencing (NGS) is a high-throughput technology that can be used as a more time- and cost-effective tool for identifying molecular diagnoses for complex genetic conditions, such as neuromuscular disorders.Methods:One hundred and sixty-nine patients referred to a Canadian neuromuscular clinic for evaluation of possible muscle disease were screened with an NGS panel of muscular dystrophy–associated genes. Patients were categorized by the reason of referral (1) muscle weakness (n=135), (2) recurrent episodes of rhabdomyolysis (n=18), or (3) idiopathic hyperCKemia (n=16).Results:Pathogenic and likely pathogenic variants were identified in 36.09% of patients (61/169). The detection rate was 37.04% (50/135) in patients with muscle weakness, 33.33% (6/18) with rhabdomyolysis, and 31.25% (5/16) in those with idiopathic hyperCKemia.Conclusions:This study shows that NGS can be a useful tool in the molecular workup of patients seen in a neuromuscular clinic. Evaluating the utility of large panels of a muscle disease-specific NGS panel to investigate the genetic susceptibilities of rhabdomyolysis and/or idiopathic hyperCKemia is a relatively new field. Twenty-eight of the pathogenic and likely pathogenic variants reported here are novel and have not previously been associated with disease.

The Limb-Girdle Muscular Dystrophies and the Dystrophinopathies

PURPOSE OF REVIEW

The classic approach to identifying and accurately diagnosing limb-girdle muscular dystrophies (LGMDs) relied heavily on phenotypic characterization and ancillary studies including muscle biopsy. Because of rapid advances in genetic sequencing methodologies, several additional LGMDs have been molecularly characterized, and the diagnostic approach to these disorders has been simplified. This article summarizes the epidemiology, clinical features, and genetic defects underlying the LGMDs.

RECENT FINDINGS

In recent years, the advent of next-generation sequencing has heralded an era of molecular diagnosis in conjunction with physical characterization. Inadvertently, this process has also led to the "next-generation aftermath," whereby variants of unknown significance are identified in most patients. Similar to the published diagnostic and treatment guidelines for Duchenne muscular dystrophy, diagnostic and treatment guidelines have recently been published for LGMDs. In addition, the first medication (based on the exon-skipping strategy) for treatment of patients with a subset of Duchenne muscular dystrophy has been recently approved by the US Food and Drug Administration (FDA).

SUMMARY

The LGMDs are a heterogeneous group of hereditary, progressive, and degenerative neuromuscular disorders that present with primary symptoms of shoulder girdle and pelvic girdle weakness. Although a combination of clinical and molecular genetic evaluations may be sufficient for accurate diagnosis of LGMDs in many cases, the contribution of imaging and histopathologic correlations still remains a critical, if not a necessary, component of evaluation in some cases.

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.