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Myosin storage myopathy
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Myosin storage myopathy

Myosin storage myopathy is a rare congenital muscle disorder characterized by progressive muscle weakness and the accumulation of abnormal protein clumps within muscle fibers.

Overview

Myosin storage myopathy is a condition that affects muscle (myopathy), causing muscle weakness that can worsen slowly over time. The signs and symptoms often begin in childhood, though they can manifest later. The severity and specific features of the condition can vary significantly, even among members of the same family.

This disorder belongs to a group of conditions known as congenital myopathies, where symptoms are typically present at birth or shortly thereafter. These conditions primarily affect skeletal muscles used for movement and, less commonly, the cardiac muscle.

Symptoms

Children with myosin storage myopathy may experience delayed walking and a waddling gait. Common clinical features include:

  • Difficulty climbing stairs and lifting arms above shoulder level.
  • Scapular winging, where the shoulder blades stick out from the back due to weak shoulder muscles.
  • Spinal curvature (scoliosis).
  • Respiratory insufficiency due to weakness in breathing muscles.
  • Cardiac muscle weakness.

Causes & Risk Factors

Myosin storage myopathy is caused by pathogenic variants in the MYH7 gene, which provides instructions for making the protein myosin-7. This protein is a major component of the thick filaments within sarcomeres—the basic units of muscle contraction.

Pathogenic variants lead to the production of non-functional myosin-7, which accumulates in skeletal muscle fibers as protein clumps. These clumps are visible during a muscle biopsy. While the exact mechanism linking these clumps to muscle weakness is not fully understood, they are a hallmark of the condition.

Inheritance

The condition is typically inherited in an autosomal dominant pattern, meaning one copy of the altered gene is sufficient to cause the disorder. In rare cases, it follows an autosomal recessive pattern, requiring both copies of the gene to have a pathogenic variant.

Frequently Asked Questions

While there is no cure, multidisciplinary care can help. Physical therapy focused on strength, flexibility, and gait training is essential. Respiratory support—such as incentive spirometry, nighttime ventilation, or non‑invasive positive pressure ventilation—may be needed if breathing muscles weaken. Orthotic devices (e.g., ankle‑foot orthoses) can assist with walking. Emerging research into gene‑based therapies is ongoing but not yet clinically available.
Regular pulmonary function tests (spirometry) and overnight pulse‑oximetry can detect early breathing problems. Symptoms such as shortness of breath, frequent colds, or snoring warrant prompt evaluation. Early intervention with chest physiotherapy, breathing exercises, and, if indicated, nocturnal ventilation can prevent respiratory failure and improve sleep quality.
definitive diagnosis usually starts with a muscle biopsy that shows characteristic myosin clumps in the fibers. Genetic testing for pathogenic variants in the MYH7 gene is then performed, often using next‑generation sequencing panels for congenital myopathies. Electromyography (EMG) may help rule out other neuromuscular disorders, and a cardiac evaluation (echocardiogram or ECG) is recommended because MYH7 mutations can also affect the heart.
Progression is typically slow, with mild weakness in early childhood that may worsen over decades. Many patients maintain independent ambulation into adulthood, but some develop significant gait difficulties, respiratory insufficiency, or cardiac involvement by middle age. Regular follow‑up with a neurologist and cardiologist helps anticipate and manage these changes.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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