Pathomechanics of Gowers' sign: a video analysis of a spectrum of Gowers' maneuvers

Identification and functional characterization of a novel heterozygous splice‑site mutation in the calpain 3 gene causes rare autosomal dominant limb‑girdle muscular dystrophy

Limb-girdle muscular dystrophies are a group of extremely heterogenous neuromuscular disorders that manifest with gradual and progressive weakness of both proximal and distal muscles. Autosomal dominant limb-girdle muscular dystrophy (LGMDD4) or calpainopathy is a very rare form of myopathy characterized by weakness and atrophy of both proximal and distal muscles with a variable age of onset. LGMDD4 is caused by germline heterozygous mutations of the calpain 3 (CAPN3) gene. Patients with LGMDD4 often show extreme phenotypic heterogeneity; however, most patients present with gait difficulties, increased levels of serum creatine kinase, myalgia and back pain. In the present study, a 16-year-old male patient, clinically diagnosed with LGMDD4, was investigated. The proband had been suffering from weakness and atrophy of both of their proximal and distal muscles, and had difficulty walking and standing independently. The serum creatine kinase levels (4,754 IU/l; normal, 35-232 IU/l) of the patient were markedly elevated. The younger sister and mother of the proband were also clinically diagnosed with LGMDD4, while the father was phenotypically normal. Whole exome sequencing identified a heterozygous novel splice-site (c.2440-1G>A) mutation in intron 23 of the CAPN3 gene in the proband. Sanger sequencing confirmed that this mutation was also present in both the younger sister and mother of the proband, but the father was not a carrier of this mutation. This splice-site (c.2440-1G>A) mutation causes aberrant splicing of CAPN3 mRNA, leading to the skipping of the last exon (exon 24) of CAPN3 mRNA and resulting in the removal of eight amino acids from the C-terminal of domain IV of the CAPN3 protein. Hence, this splice site mutation causes the formation of a truncated CAPN3 protein (p.Trp814*) of 813 amino acids instead of the wild-type CAPN3 protein that consists of 821 amino acids. This mutation causes partial loss of domain IV (PEF domain) in the CAPN3 protein, which is involved in calcium binding and homodimerization; therefore, this is a loss-of-function mutation. Relative expression of the mutated CAPN3 mRNA was reduced in comparison with the wild-type CAPN3 mRNA in the proband, and their younger sister and mother. This mutation was also not present in 100 normal healthy control individuals of the same ethnicity. The present study reported the first case of CAPN3 gene-associated LGMDD4 in the Chinese population.

Development and Validation of an Outpatient Clinical Predictive Score for the Diagnosis of Duchenne Muscular Dystrophy/Becker Muscular Dystrophy in Children Aged 2-18 Years

Introduction

There is no bedside clinical examination-based prediction score for Duchenne muscular dystrophy/Becker muscular dystrophy (DMD/BMD) in children with neuromuscular diseases (NMDs) presenting with proximal limb-girdle weakness.

Methods

We compared the details of 200 cases of lower motor neuron type of weakness and had some proximal limb-girdle muscle weakness and divided them into 2 groups: with/without a confirmed diagnosis of DMD/BMD. We determined the predictive factors associated with a diagnosis of DMD/BMD using multivariate binary logistic regression. We assessed our proposed prognostic model using both discrimination and calibration and subsequently used the bootstrap method to successfully validate the model internally.

Results

A total of 121 patients had DMD/BMD and the rest of the patients had other diagnoses. Male gender, presence of Gower's sign, valley sign, toe walking, calf pseudohypertrophy, and tongue hypertrophy were independent predictors for a confirmed diagnosis of DMD/BMD and included in the final CVT2MG score (Calf pseudohypertrophy, Valley sign, Toe walking, Tongue hypertrophy, Male gender, and Gower's sign). The final model showed good discrimination (AUC = 87.4% [95% CI: 80.5-92.3%, P < 0.001]) and calibration (P = 0.57). A score of 6 or above appeared to be the best cutoff for discriminating between the DMD/BMD group and the rest of the group with both sensitivity and specificity of 98%. The interrater reliability was almost perfect between two pediatric neurologists and strong between a pediatric neurologist and a pediatric neurology trainee resident (k = 0.91 and 0.87).

Conclusion

The CVT2MG score has good sensitivity and specificity in predicting a confirmed diagnosis of DMD/BMD in subsequent tests.

Recent Trends in Antisense Therapies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a debilitating and fatal genetic disease affecting 1/5000 boys globally, characterized by progressive muscle breakdown and eventual death, with an average lifespan in the mid-late twenties. While no cure yet exists for DMD, gene and antisense therapies have been heavily explored in recent years to better treat this disease. Four antisense therapies have received conditional FDA approval, and many more exist in varying stages of clinical trials. These upcoming therapies often utilize novel drug chemistries to address limitations of existing therapies, and their development could herald the next generation of antisense therapy. This review article aims to summarize the current state of development for antisense-based therapies for the treatment of Duchenne muscular dystrophy, exploring candidates designed for both exon skipping and gene knockdown.

Idiopathic Toe-Walking in Children and Adolescents: Diagnosis, Natural History, and Treatment Options

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Idiopathic toe-walking is a diagnosis of exclusion.

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The natural history of idiopathic toe-walking has not been studied in many children; we identified only 1 prospective study. Of children without equinus contractures who were toe-walking before the age of 5.5 years, 59% had spontaneous resolution of toe-walking by 5.5 years of age, and 79%, by the age of 10 years.

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Adverse consequences of toe-walking into adulthood have not been reported, but may exist, and further research is needed to define and clarify.

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If parents desire treatment to resolve their child's toe-walking, surgical lengthening of the Achilles tendon is the treatment with the highest chance of success and lowest relapse rate, and thus far, no complications have been reported in any surgical series.

The skeletal muscle phenotype of children with Neurofibromatosis Type 1 - A clinical perspective

Neurofibromatosis type 1 (NF1) can affect multiple systems in the body. An under recognised phenotype is one of muscle weakness. Clinical studies using dynamometry and jumping mechanography have demonstrated that children with NF1 are more likely to have reduced muscle force and power. Many children with NF1 are unable to undertake physical activities to the same level as their peers, and report leg pains on physical activity and aching hands on writing. Children and adolescents with NF1 reporting symptoms of muscle weakness should have a focused assessment to exclude alternative causes of muscle weakness. Assessments of muscle strength and fine motor skills by physiotherapists and occupational therapists can provide objective evidence of muscle function and deficits, allowing supporting systems in education and at home to be implemented. In the absence of an evidence base for management of NF1-related muscle weakness, we recommend muscle-strengthening exercises and generic strategies for pain and fatigue management. Currently, trials are underway involving whole-body vibration therapy and carnitine supplementation as potential future management options.

Bilateral Anterior Knee Pain in a High School Cross-Country Runner: An Atypical Etiology

Anterior knee pain is a common complaint found in distance runners, and can be the end result of a variety of benign processes. A 17-year-old female cross-country runner presented to a sports medicine clinic with insidious onset of bilateral patellofemoral pain (PFP). In the workup of the significant quadriceps weakness discovered on her initial examination, a principal contributing cause of her PFP, she was found to have a form of spinal muscular atrophy, an uncommon neurodegenerative disease that typically requires multidisciplinary medical care. Her case provides a good example for clinicians to consider, at times, an in-depth assessment of the root causes of benign conditions.

Bridging the Gap: An Osteopathic Primary Care–Centered Approach to Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a deadly and incurable disease typically diagnosed in early childhood. Presently, the delay between a caregiver's initial concern and the primary care physician obtaining creatine kinase levels—the most important screening test—is more than a year. It is imperative to diagnose DMD as soon as possible because early treatment has the potential to double the patient's lifespan. In addition, because of geographic and economic disadvantages, multidisciplinary DMD treatment centers are not readily available to all patients. Therefore, the challenge of early diagnosis and treatment coordination rests with the primary care physician. The present review provides osteopathic primary care physicians with current and relevant information regarding DMD diagnosis and management.

A Practical Approach to Juvenile Dermatomyositis and Juvenile Scleroderma

Juvenile dermatomyositis and juvenile scleroderma are rare multisystem autoimmune disorders. Although they share some pathognomonic hallmarks with adult onset myositis or scleroderma, there are significant differences in presentation, characteristics and associated features when the diseases present in childhood. In view of this, and the rarity of the conditions, it is important for care to be led by teams with expertise in pediatric rheumatology conditions. Prognosis has improved significantly in the West; likely due to early diagnosis and aggressive treatment with immunosuppressive medications. However, this trend is not replicated in the developing world. Early recognition of these diseases is crucial to achieve rapid and sustained remission and prevent disease or medication associated complications. This article aims to provide a practical overview for recognition, diagnosis and treatment of these conditions.

Use of patient video cases in medical education

Patient video cases (PVCs) are brief video recordings of patients during spontaneous or instructed activity. PVCs are true to life and can be replayed, enabling the establishment of highly interactive, contextual and safe learning environments, with a minimum of facilitation. This article describes the use of workshops in which PVCs are used to assist with the development of observational skills and clinical reasoning in medical students and postgraduates. We describe why PVCs are a valuable addition to an educator's portfolio of resources, what evidence there is for their effectiveness, how to use videos for teaching, and some practical advice and tips on their collection and storage.

Diaphragm remodeling and compensatory respiratory mechanics in a canine model of Duchenne muscular dystrophy

Ventilatory insufficiency remains the leading cause of death and late stage morbidity in Duchenne muscular dystrophy (DMD). To address critical gaps in our knowledge of the pathobiology of respiratory functional decline, we used an integrative approach to study respiratory mechanics in a translational model of DMD. In studies of individual dogs with the Golden Retriever muscular dystrophy (GRMD) mutation, we found evidence of rapidly progressive loss of ventilatory capacity in association with dramatic morphometric remodeling of the diaphragm. Within the first year of life, the mechanics of breathing at rest, and especially during pharmacological stimulation of respiratory control pathways in the carotid bodies, shift such that the primary role of the diaphragm becomes the passive elastic storage of energy transferred from abdominal wall muscles, thereby permitting the expiratory musculature to share in the generation of inspiratory pressure and flow. In the diaphragm, this physiological shift is associated with the loss of sarcomeres in series (∼ 60%) and an increase in muscle stiffness (∼ 900%) compared with those of the nondystrophic diaphragm, as studied during perfusion ex vivo. In addition to providing much needed endpoint measures for assessing the efficacy of therapeutics, we expect these findings to be a starting point for a more precise understanding of respiratory failure in DMD.