Congenital muscular dystrophies

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.

The Presentation of Two Unrelated Clinical Cases from the Republic of North Ossetia-Alania with the Same Previously Undescribed Variant in the COL6A2 Gene

Here, we described three affected boys from two unrelated families of Ossetian-Digor origin from the Republic of North Ossetia-Alania who were admitted to the Research Centre for Medical Genetics with unspecified muscular dystrophy. High-throughput sequencing was performed and revealed two novel frameshift variants in the COL6A2 gene (NM_001849.3) in a heterozygous state each in both cases: c.508_535delinsCTGTGG and c.1659_1660del (case 1) and c.1689del and c.1659_1660del (case 2). In two cases, the same nucleotide variant in the COL6A2 gene (c.1659_1660del) was observed. We have suggested that the variant c.1659_1660del may be common in the Ossetian-Digor population because two analyzed families have the same ancestry from the same subethnic group of Ossetians). The screening for an asymptomatic carriage of the nucleotide variant c.1659_1660del in 54 healthy donors from Ossetian-Digor population revealed that the estimated carrier frequency is 0.0093 (CI: 0.0002–0.0505), which is high for healthy carriers of the pathogenic variant. Molecular genetic, anamnestic data and clinical examination results allowed us to diagnose Ullrich muscular dystrophy in those affected boys. Genetic heterogeneity and phenotypic diversity of muscular dystrophies complicate diagnosis. It is important to make a differential diagnosis of such conditions and use HTS methods to determine the most accurate diagnosis.

3D in vitro Models of Pathological Skeletal Muscle: Which Cells and Scaffolds to Elect?

Skeletal muscle is a fundamental tissue of the human body with great plasticity and adaptation to diseases and injuries. Recreating this tissue in vitro helps not only to deepen its functionality, but also to simulate pathophysiological processes. In this review we discuss the generation of human skeletal muscle three-dimensional (3D) models obtained through tissue engineering approaches. First, we present an overview of the most severe myopathies and the two key players involved: the variety of cells composing skeletal muscle tissue and the different components of its extracellular matrix. Then, we discuss the peculiar characteristics among diverse in vitro models with a specific focus on cell sources, scaffold composition and formulations, and fabrication techniques. To conclude, we highlight the efficacy of 3D models in mimicking patient-specific myopathies, deepening muscle disease mechanisms or investigating possible therapeutic effects.

Neuromuscular Diseases of the Newborn

The peripheral nervous system (PNS) is composed of motor neurons, nerve roots, plexuses, peripheral nerves (motor, sensory and autonomic), neuromuscular junction, and skeletal muscles. Disorders of the PNS in neonates most frequently cause weakness, hypotonia, and contractures, which may be generalized or focal. Since these findings may also occur with brain and spinal cord lesions, key features of the history and neurologic exam, together with diagnostic testing, are helpful in reaching a diagnosis. This review covers the diagnostic approach to PNS disorders in the neonate and includes a discussion of representative diseases of the motor neuron, brachial plexus, peripheral nerves, neuromuscular junction, and muscles. The importance of reaching a precise genetic diagnosis is highlighted with a discussion of current and emerging treatments for neonatal PNS diseases, particularly spinal muscular atrophy.

Loss of function of Colgalt1 disrupts collagen post-translational modification and causes musculoskeletal defects

In a screen for organogenesis defects in N-ethyl-N-nitrosourea (ENU)-induced mutant mice, we discovered a line carrying a mutation in Colgalt1 [collagen beta(1-O)galactosyltransferase type 1], which is required for proper galactosylation of hydroxylysine residues in a number of collagens. Colgalt1 mutant embryos have not been previously characterized; here, we show that they exhibit skeletal and muscular defects. Analysis of mutant-derived embryonic fibroblasts reveals that COLGALT1 acts on collagen IV and VI, and, while collagen VI appears stable and its secretion is not affected, collagen IV accumulates inside of cells and within the extracellular matrix, possibly due to instability and increased degradation. We also generated mutant zebrafish that do not express the duplicated orthologs of mammalian Colgalt1. The double-homozygote mutants have muscle defects; they are viable through the larvae stage but do not survive to 10 days post-fertilization. We hypothesize that the Colgalt1 mutant could serve as a model of a human connective tissue disorder and/or congenital muscular dystrophy or myopathy.

Summary: The authors characterized a novel mouse mutant that has a defect in collagen glycosylation, which appears to affect muscle development. There is very little functional characterization of the affected gene, but this study provides analysis of its embryonic phenotype and the biochemistry of the null mutant, as well as the phenotype of null-mutant zebrafish.

A child diagnosed with rigid spine syndrome complicated by ventilatory disorders: a nursing case report

Rigid spine syndrome is a rare myopathy in children and has a poor prognosis because of its lack of treatment and eventual ventilatory failure. We report the case of a 10-year-old child with RSS and ventilatory disorders. We provided care to the child using bilevel positive airway pressure (BiPAP) non-invasive mechanical ventilation and continuous monitoring of transcutaneous carbon dioxide pressure. A 10-year-old Han Chinese girl presented (6 April 6 2016) to the Shanghai Children’s Medical Center with ventilatory disorders, including hypoxia and hypercapnia. Transcutaneous oxygen saturation with mask oxygen inspiration was 90%. BiPAP non-invasive ventilator-assisted ventilation was continuously used. Through continuous non-invasive ventilation and carbon dioxide monitoring, the symptoms of dyspnea in this child were effectively controlled and improved. She was discharged on April 19 with instructions to continue using BiPAP at home and transcutaneous oxygen saturation was maintained at 94% to 98%. This case highlights that nursing of patients with rigid spine syndrome and ventilatory disorders should focus on evaluating the effect of non-invasive mechanical ventilation, prevention of complications, and continuous nursing after discharge. Additionally, continuous monitoring of transcutaneous carbon dioxide pressure is feasible for evaluating the effect of BiPAP.

Three novel recessive mutations in LAMA2, SYNE1, and TTN are identified in a single case with congenital muscular dystrophy

Congenital muscular dystrophies (CMD) are a group of heterogeneous disorders. Here, targeted next generation sequencing of 168 CMD-associated genes was performed on collected clinic samples to identify potential mutations. A loss-of-function mutation (c.4676-4682delGCTGCAA; p.Cys1560Thrfs*33) of the LAMA2 gene in a consanguineous family was identified and confirmed by Sanger sequencing. The second recessive mutation in SYNE1 (c.2881C>T; p.Arg961Trp) was found in the SAP motif, which was predicted to be involved in chromosomal organization. The third homozygous mutation (c.32462C>T; p.Pro10821Leu) in TTN was mapped to the third PPAK motif of the encoded protein. Muscle biopsies of the proband showed large variations in muscle fiber size, necrotic and regenerating fibers and an increase in endomysial collagen tissue. To the best of our knowledge, this is the first case with CMD and mildly enlarged heart, carrying three novel recessive mutations in LAMA2, SYNE1, and TTN.

Tmem2 regulates cell-matrix interactions that are essential for muscle fiber attachment

Skeletal muscle morphogenesis depends upon interactions between developing muscle fibers and the extracellular matrix (ECM) that anchors fibers to the myotendinous junction (MTJ). The pathways that organize the ECM and regulate its engagement by cell-matrix adhesion complexes (CMACs) are therefore essential for muscle integrity. Here, we demonstrate the impact of transmembrane protein 2 (tmem2) on cell-matrix interactions during muscle morphogenesis in zebrafish. Maternal-zygotic tmem2 mutants (MZtmem2) exhibit muscle fiber detachment, in association with impaired laminin organization and ineffective fibronectin degradation at the MTJ. Similarly, disorganized laminin and fibronectin surround MZtmem2 cardiomyocytes, which could account for their hindered movement during cardiac morphogenesis. In addition to ECM defects, MZtmem2 mutants display hypoglycosylation of α-dystroglycan within the CMAC, which could contribute to the observed fiber detachment. Expression of the Tmem2 ectodomain can rescue aspects of the MZtmem2 phenotype, consistent with a possible extracellular function of Tmem2. Together, our results suggest that Tmem2 regulates cell-matrix interactions by affecting both ECM organization and CMAC activity. These findings evoke possible connections between the functions of Tmem2 and the etiologies of congenital muscular dystrophies, particularly dystroglycanopathies.

Acceptance, Usability and Health Applications of Virtual Worlds by Older Adults: A Feasibility Study

BACKGROUND

Virtual worlds allow users to communicate and interact across various environments, scenarios, and platforms. Virtual worlds present opportunities in health care to reduce the burden of illness and disability by supporting education, rehabilitation, self-management, and social networking. The application of virtual worlds to older adults who bear the burden and cost of health conditions associated with age has not been evaluated.

OBJECTIVE

The aim of this study is to explore the usability, ease of use, and enjoyment of a virtual world by older adults, the types of virtual world activities that older adults may engage in, and the perceptions of older adults regarding the application of virtual worlds in health care.

METHODS

This quasi-experimental pre-post design research was guided by the Technology Acceptance Model (TAM). Participants were recruited from a Lifelong Learning Institute (LLI) program at Nova Southeastern University. Participants attended four training sessions over a 5-week period in the Second Life (SL) virtual world. Subjects were surveyed before and after the training on perceived ease of use, attitudes towards technology, behavioral intention to use the system, facilitating conditions, effort expectancy, and self-efficacy.

RESULTS

Older adults (N=19) completed the informed consent and attended the first training session, and 11 participants (58%, 11/19) completed the full training and the post survey. Completers (82%, 9/11) were more likely than non-completers (37%, 3/8) to consider themselves technologically savvy (P=.048), and to express confidence in being able to use the virtual world (100%, 11/11 vs 37%, 3/8; P=.002). All completers (100%, 11/11) perceived that SL has application in health behaviors and disease and reducing social isolation among people who are homebound. Of the completers, 10 (91%, 10/11) responded that they enjoyed learning how to use SL. Completers suggested that future trainings include more assistants and smaller groups.

CONCLUSIONS

This pilot study suggests that virtual worlds can be both a feasible and an applicable method to promote health among some seniors. Future research on virtual worlds with older populations should consider using state-of-the art technology including large monitors, providing a minimum of one trainer for every two to three participants, and distributing a comprehensive training manual at the start of the training to support organization and recall.

Ophthalmological Findings of Turkish Children With Muscular Dystrophies

PURPOSE

To present the results of ophthalmological examinations in children with muscular dystrophies and highlight the importance of their ophthalmological evaluation.

METHODS

Retrospective analysis of the ophthalmological examination records in 74 children with a type of muscular dystrophy, examined between January 2011 and January 2015, was performed.

RESULTS

The most common type of muscular dystrophy observed in our patients was Duchenne muscular dystrophy (67.5%), followed by Becker muscular dystrophy (9.4%), myotonic dystrophy (8%), limb-girdle muscular dystrophy (6.7%), merosin-negative muscular dystrophy (4%), and Ullrich muscular dystrophy (4%). Ten cases of Duchenne muscular dystrophy had both macular and retinal pigmentary changes (20%) and 9 had abnormal electroretinographies with decreased photopic and scotopic responses. Ptosis was the most common finding (83.3%). No abnormalities of light reflexes, pupil size, or saccadic and smooth pursuit movements were seen among cases with myotonic dystrophy.

CONCLUSIONS

Ophthalmological problems are commonly seen in children with muscular dystrophies. Simple ophthalmological screening and early intervention can improve their communication skills by way of increasing their visual talents.

LAMA2-related myopathy: Frequency among congenital and limb-girdle muscular dystrophies

INTRODUCTION

Muscular dystrophy caused by LAMA2-gene mutations is an autosomal recessive disease typically presenting as a severe, early-onset congenital muscular dystrophy (CMD). However, milder cases with a limb-girdle type muscular dystrophy (LGMD) have been described.

METHODS

In this study, we assessed the frequency and phenotypic spectrum of LAMA2-related muscular dystrophy in CMD (n = 18) and LGMD2 (n = 128) cohorts identified in the last 15 years in eastern Denmark. The medical history, brain-MRI, muscle pathology, muscle laminin-α2 expression, and genetic analyses were assessed.

RESULTS

Molecular genetics revealed 2 pathogenic LAMA2 mutations in 5 of 18 CMD and 3 of 128 LGMD patients, corresponding to a LAMA2-mutation frequency of 28% in the CMD and 2.3% in the LGMD cohorts, respectively.

CONCLUSIONS

This study demonstrates a wide clinical spectrum of LAMA2-related muscular dystrophy and its prevalence in an LGMD2 cohort, which indicates that LAMA2 muscular dystrophy should be included in the LGMD2 nomenclature.

Model organisms in the fight against muscular dystrophy: lessons from drosophila and Zebrafish

Muscular dystrophies (MD) are a heterogeneous group of genetic disorders that cause muscle weakness, abnormal contractions and muscle wasting, often leading to premature death. More than 30 types of MD have been described so far; those most thoroughly studied are Duchenne muscular dystrophy (DMD), myotonic dystrophy type 1 (DM1) and congenital MDs. Structurally, physiologically and biochemically, MDs affect different types of muscles and cause individual symptoms such that genetic and molecular pathways underlying their pathogenesis thus remain poorly understood. To improve our knowledge of how MD-caused muscle defects arise and to find efficacious therapeutic treatments, different animal models have been generated and applied. Among these, simple non-mammalian Drosophila and zebrafish models have proved most useful. This review discusses how zebrafish and Drosophila MD have helped to identify genetic determinants of MDs and design innovative therapeutic strategies with a special focus on DMD, DM1 and congenital MDs.