Search

Muscle weakness in childhood can be caused by a lesion at any point extending from the motor cortex, brainstem and spinal cord to the anterior horn cell, peripheral nerve, neuromuscular junction and muscle. A comprehensive history and physical examination is essential to aid classification of the neuromuscular disorder and direct gene testing. The more common disorders such as spinal muscular atrophy, Duchenne muscular dystrophy, myotonic dystrophy and facioscapulohumeral dystrophy may be diagnosed on direct gene testing based on the history and clinical examination. The congenital myopathies are classified based on structural abnormalities on muscle biopsy, while protein abnormalities on immunohistochemistry and immunoblotting aid classification of the muscular dystrophies. In this review, we provide an approach to diagnosis of a child with weakness, with a focus on the inherited neuromuscular disorders, and the features on history, examination and investigation that help to distinguish between them. [ABSTRACT FROM AUTHOR]

The article discusses the study by Wein, N. and colleagues to demonstrate that initiation of Duchenne muscular dystrophy (DMD) exon 6 translation is driven by an internal ribosome entry site (IRES) in exon 5 nucleic acid sequence and this allows translation of truncated form of dystrophin protein. It states that mass spectrometry on muscle biopsy tissue of an asymptomatic individual was carried out and a form of dystrophin was detected and therapeutic use of IRES modulation was established.

Abstract: Foot weakness occurs in many paediatric neuromuscular disorders, which overtime can cause considerable functional motor difficulties. Measuring foot strength with hand-held dynamometry is reliable in preschool-age children, but its validity in this age group is unknown. If foot strength measures are collected as endpoints in clinical trials, they should represent functionally meaningful outcomes. We evaluated the foot strength-motor function relationship in 60 healthy children aged 2–4 years. Foot strength measures included inversion, eversion, dorsiflexion and plantarflexion using hand-held dynamometry. Motor function parameters included time to run 10-m, standing long jump distance and vertical jump height. Measures of foot strength showed significant correlations with all measures of motor function (r =0.40–0.57, p <0.001). Hand-held dynamometry may be used as a valid and functionally meaningful measure of foot strength in very young children. [Copyright &y& Elsevier]

Duchenne muscular dystrophy (DMD) is the second most common fatal genetic disease in humans and is characterized by the absence of a functional copy of the protein dystrophin from skeletal muscle. In dystrophin-negative humans and rodents, regenerated skeletal muscle fibers show abnormal branching. The number of fibers with branches and the complexity of branching increases with each cycle of degeneration/regeneration. Previously, using the mdx mouse model of DMD, we have proposed that once the number and complexity of branched fibers present in dystrophic fast-twitch EDL muscle surpasses a stable level, we term the "tipping point," the branches, in and of themselves, mechanically weaken the muscle by rupturing when subjected to high forces during eccentric contractions. Here, we use the slow-twitch soleus muscle from the dystrophic mdx mouse to study prediseased "periambulatory" dystrophy at 2-3 wk, the peak regenerative "adult" phase at 6-9 wk, and "old" at 58-112 wk. Using isolated mdx soleus muscles, we examined contractile function and response to eccentric contraction correlated with the amount and complexity of regenerated branched fibers. The intact muscle was enzymatically dispersed into individual fibers in order to count fiber branching and some muscles were optically cleared to allow laser scanning confocal microscopy. We demonstrate throughout the lifespan of the mdx mouse that dystrophic slow-twitch soleus muscle is no more susceptible to eccentric contraction-induced injury than age-matched littermate controls and that this is correlated with a reduction in the number and complexity of branched fibers compared with fast-twitch dystrophic EDL muscles. [ABSTRACT FROM AUTHOR]

A striking pathological feature of dystrophinopathies is the presence of morphologically abnormal branched skeletal muscle fibers. The deterioration of muscle contractile function in Duchenne muscular dystrophy is accompanied by both an increase in number and complexity of these branched fibers. We propose that when number and complexity of branched fibers reaches a critical threshold, or "tipping point," the branches in and of themselves are the site of contraction-induced rupture. In the present study, we use the dystrophic mdx mouse and littermate controls to study the prediseased dystrophic fast-twitch extensor digitorum longus (EDL) muscle at 2-3 wk, the peak myonecrotic phase at 6-9 wk, and finally, "old," at 58-112 wk. Using a combination of isolated muscle function contractile measurements coupled with single-fiber imaging and confocal microscope imaging of cleared whole muscles, we identified a distinct pathophysiology, acute fiber rupture at branch nodes, which occurs in "old" fast-twitch EDL muscle approaching the end stage of the dystrophinopathy muscle disease, where the EDL muscles are entirely composed of complexed branched fibers. This evidence supports our concept of "tipping point" where the number and extent of fiber branching reach a level where the branching itself terminally compromises muscle function, irrespective of the absence of dystrophin. [ABSTRACT FROM AUTHOR]

Aim: To investigate whether in-the-moment diary reports of daily experience, taken collectively, are a valid representation of health-related quality of life (HRQL).Methods: A total of 35 boys with Duchenne muscular dystrophy (DMD) were recruited through four neuromuscular care providers across Australia. Participants completed the PedsQL™ Generic Core scales and one week of experience-sampling diary reporting on a personal digital assistant. Rasch analysis was undertaken on the diary data to derive a single valid measure score. The resulting measure score for each participant was correlated with the summary score from the PedsQL™ Generic Core scales to examine whether daily experience was representative of HRQL.Results: The daily diary method showed good metric properties, with adequate goodness of fit for data from items and participants suggesting unidimensionality of the construct: quality of everyday experience. The correlation of the daily diary measure score with overall PedsQL™ summary score showed moderate agreement (r = .60, p = 0.001).Conclusions: The benefits of measuring daily quality of life include detailed descriptions of day-to-day experiences of children without the need for retrospective recall. Diary methods on an electronic platform or software application for personal devices may be a useful tool to understand HRQL as the repeated measures data provide a detailed experience directly from the child and the platform makes data completion highly motivating. [ABSTRACT FROM AUTHOR]

Aim: To investigate parent-reported health status of boys with Duchenne muscular dystrophy (DMD) compared with a large Australian normative population and a cohort of children with Charcot-Marie-Tooth disease type 1A (CMT1A). Methods: The Child Health Questionnaire parent form (CHQ-PF50) was completed by parents of 34 boys with confirmed DMD. Seventeen parents were followed up at 6 months. CHQ-PF50 data were compared with 2620 age-matched norms and 90 children with CMT1A. Results: All domains of the CHQ-PF50 for the DMD cohort were significantly lower than the general paediatric population, particularly for physical functioning ( t=−17.2, P < 0.001) and the child's ability to fulfil school and social roles because of physical limitations ( t=−9.4, P < 0.001). Parents experienced greatest emotional impact of their child's DMD around the time of loss of ambulation. Children with DMD had lower health status compared with children with CMT1A with the exception of the behaviour and pain domains. Physical functioning worsened during 6 months ( P= 0.04); no other changes in health status were observed at follow-up. Conclusions: Parents report the impact of DMD on health status to be considerably worse when compared with CMT1A. Interventions should target minimising the impact of physical limitations on role functioning. [ABSTRACT FROM AUTHOR]

Cardiomyopathy contributes to morbidity and mortality in Duchenne muscular dystrophy (DMD), a progressive muscle-wasting disorder. A major feature of the hearts of DMD patients and the mdx mouse model of the disease is cardiac fibrosis. Connective tissue growth factor (CTGF) is involved in the fibrotic process in many organs. This study utilized the mdx mouse model to assess the role of CTGF and other extracellular matrix components during the development of fibrosis in the dystrophic heart. Left ventricular function of mdx and control mice at 6, 29 and 43 weeks was measured by echocardiography. Young (6 weeks old) mdx hearts had normal function and histology. At 29 weeks of age, mdx mice developed cardiac fibrosis and increased collagen expression. The onset of fibrosis was associated with increased CTGF transcript and protein expression. Increased intensity of CTGF immunostaining was localized to fibrotic areas in mdx hearts. The upregulation of CTGF was also concurrent with increased expression of tissue inhibitor of matrix metalloproteinases (TIMP-1). These changes persisted in 43 week old mdx hearts and were combined with impaired cardiac function and increased gene expression of transforming growth factor (TGF)-β1 and matrix metalloproteinases (MMP-2, MMP-9). In summary, an association was observed between cardiac fibrosis and increased CTGF expression in the mdx mouse heart. CTGF may be a key mediator of early and persistent fibrosis in dystrophic cardiomyopathy. [ABSTRACT FROM AUTHOR]

Transmembrane water transport is mediated by aquaporins (AQPs), of which AQP1 and AQP4 are expressed in skeletal muscle. AQP4 expression is reduced in Duchenne muscular dystrophy (DMD) patients, and is reported to correlate with decreased α1-syntrophin and altered osmotic permeability. In this study, we assessed the relationship between AQP1, AQP4, dystrophin and α1-syntrophin in dystrophinopathy and dysferlinopathy patients. Muscle biopsies of patients with DMD ( n = 8) and limb–girdle muscular dystrophy type 2B (LGMD2B; n = 5) were screened for AQP1 and AQP4 expression by real-time quantitative RT-PCR or Western blot and immunohistochemistry. AQP expression was further analyzed in primary myotubes derived from DMD and LGMD2B patients by cell culture and immunohistochemistry. AQP1 transcript and protein expression was significantly elevated in DMD biopsies, and was localized to the sarcolemma of muscle fibers and endothelia of muscle capillaries. AQP4 was significantly reduced despite normal dystrophin and α1-syntrophin in dysferlinopathy patients, while expression of AQP1 was variably upregulated. Expression of AQP1 and AQP4 was normal in patient-derived primary myotubes, suggesting that altered AQPs observed in biopsies are likely secondary to the dystrophic process. Our study shows that AQP4 downregulation can occur in muscular dystrophies with either normal or disrupted expression of dystrophin-associated proteins, and that this might be associated with upregulation of AQP1. [ABSTRACT FROM AUTHOR]