A de novo mutation of the MYH7 gene in a large Chinese family with autosomal dominant myopathy

MYH7 in cardiomyopathy and skeletal muscle myopathy

Myosin heavy chain gene 7 (MYH7), a sarcomeric gene encoding the myosin heavy chain (myosin-7), has attracted considerable interest as a result of its fundamental functions in cardiac and skeletal muscle contraction and numerous nucleotide variations of MYH7 are closely related to cardiomyopathy and skeletal muscle myopathy. These disorders display significantly inter- and intra-familial variability, sometimes developing complex phenotypes, including both cardiomyopathy and skeletal myopathy. Here, we review the current understanding on MYH7 with the aim to better clarify how mutations in MYH7 affect the structure and physiologic function of sarcomere, thus resulting in cardiomyopathy and skeletal muscle myopathy. Importantly, the latest advances on diagnosis, research models in vivo and in vitro and therapy for precise clinical application have made great progress and have epoch-making significance. All the great advance is discussed here.

Understanding Musculoskeletal Disorders Through Next-Generation Sequencing

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An insight into musculoskeletal disorders through advancements in next-generation sequencing (NGS) promises to maximize benefits and improve outcomes through improved genetic diagnosis.

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The primary use of whole exome sequencing (WES) for musculoskeletal disorders is to identify functionally relevant variants.

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The current evidence has shown the superiority of NGS over conventional genotyping for identifying novel and rare genetic variants in patients with musculoskeletal disorders, due to its high throughput and low cost.

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Genes identified in patients with scoliosis, osteoporosis, osteoarthritis, and osteogenesis imperfecta using NGS technologies are listed for further reference.

Clinical features and genotypes of Laing distal myopathy in a group of Chinese patients, with in-frame deletions of MYH7 as common mutations

Background

Laing distal myopathy is a rare autosomal dominant inherited distal myopathy caused by mutations of the MYH7 gene affecting mainly the rod region. We described the clinical features, muscle MRI and pathological changes as well as genetic mutations in a group of Chinese patients with Laing distal myopathy.

Results

Six patients with the confirmed diagnoses of Laing distal myopathy were recruited. Ankle dorsiflexion and finger extension weakness, as well as neck flexion weakness were common in our patients. Myopathic as well as neurogenic lesions were suggested by electromyography in different patients. Respiratory abnormality of sleep apnea was detected in two of our patients stressing the necessity of close respiratory monitoring in this disease. Muscle MRIs showed similar features of concentric fatty infiltration of anterior thigh muscles together with early involvement of tibialis anterior and extensor hallucis longus. However, muscle pathological presentations were varied depending on the biopsied muscles and the severity of the disease. In-frame deletions of the MYH7 gene made up 3/4 of mutations in our patients, suggesting that these are common mutations of Laing distal myopathy.

Conclusions

Our study further expanded the phenotypes and genotypes of Laing distal myopathy. In-frame deletions of the MYH7 gene are common causes of Laing distal myopathy.

[A case of Japanese Laing type distal myopathy with a mutation in MYH7 gene]

A 67-year-old man developed weakness and atrophy of the anterior compartment of the lower leg at age 53 years, followed by weakness of proximal muscles of the upper limb. His father had difficulties in walking in his thirties and died of heart disease at age 45 years. He also had mild respiratory weakness without cardiac involvement. Muscle histology showed spheroid or cytoplasmic bodies-like inclusions with moth-eaten appearance and irregular intramyofibrillar network. Electron microscopy revealed abnormally thickened and disorganized Z lines (Z line streaming) between the surrounding myofibrils and electron-dense globular deposits. These pathological findings apparently suggested myofibrillar myopathy. However, genetic analysis revealed a mutation (c.5566G>A, p.E1856K) in MYH7 gene, that is responsible for Laing-type distal myopathy (LDM). This mutation was previously reported in a study from Austria. This is the first report of LDM in the Japanese population .

MYH7 mutation associated with two phenotypes of myopathy

The mutations of MYH7 (slow skeletal/β-cardiac myosin heavy chain) are commonly found in familial hypertrophic/dilated cardiomyopathy, and also can cause Laing early-onset distal myopathy (LDM), myosin storage myopathy (MSM), and congenital myopathy with fiber-type disproportion (CFTD). Here we report two cases whose diagnosis was hereditary myopathy according to clinical feature and muscle pathology analysis. High-throughput genomic sequencing (next generation sequencing) was performed to validate the diagnosis. Two MYH7 mutations, p.R1845W and p.E1687del, were identified. p.R1845W was found in a male patient showing weakness of both terminal lower legs without foot drop. Muscle pathology stainings characteristically showed the hyaline body in the intracytoplasmic location. The novel mutation p.E1687del was found in a family with seven patients. The proband showed foot drop, scoliosis, and winged scapula, while his mother only showed mild foot drop and winged scapula. Muscle pathology analysis showed congenital centronucleus myopathy. Both cases only showed muscular disorder and had no cardiomyopathy. This study, for the first time, reports the MYH7 mutations associated with centronucleus myopathy.