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Description
Myosin storage myopathy is a condition that affects muscle (myopathy). This disorder causes muscle weakness that can worsen slowly over time. The signs and symptoms of myosin storage myopathy often begin in childhood, although they can begin later. The specific features of myosin storage myopathy and the severity of the condition can vary, even among members of the same family.
Children with myosin storage myopathy may start walking later than usual and have a waddling gait. They can have trouble climbing stairs and difficulty lifting their arms above shoulder level. Weak shoulder muscles often make the shoulder blades (scapulae) "stick out" from the back, a sign known as scapular winging. Affected individuals may also have a spine that curves to the side (scoliosis). Some individuals can also develop weakness of the muscles that control breathing (respiratory insufficiency) or weakness of the heart (cardiac) muscle.
Myosin storage myopathy belongs to a group of disorders called congenital myopathies. The signs and symptoms of congenital myopathies are often present at birth (congenital) or soon after. Congenital myopathies may affect the muscles used for movement (skeletal muscle) and, less commonly, the cardiac muscle.
Frequency
Myosin storage myopathy is rare, although the exact number of people with this condition is unknown.
Causes
Genetic changes that cause disease are called pathogenic variants. Pathogenic variants in the MYH7 gene cause myosin storage myopathy. The MYH7 gene provides instructions for making a protein known as myosin-7. This protein is found in cardiac muscle and in certain skeletal muscle fibers.
Myosin-7 is the major component of the thick filament in muscle cell structures called sarcomeres
. Sarcomeres are the basic units of muscle contraction. They are composed of overlapping thick and thin filaments that undergo cycles of attachment and release. These cycles allow the thin filaments to slide past the thick filaments, which shortens the sarcomere and causes the muscle to contract.
Pathogenic variants in the MYH7 gene can cause cells to produce a version of myosin-7 that does not function properly. The altered proteins accumulate within the skeletal muscle fibers, forming protein clumps that can be seen when muscle tissue is removed for examination (muscle biopsy). It is unclear exactly how these changes lead to the muscle weakness seen in people with myosin storage myopathy.
Inheritance
Myosin storage myopathy is typically inherited in an autosomal dominant pattern
, which means one copy of the altered gene in each cell is sufficient to cause the disorder.
In rare cases, myosin storage myopathy has followed an autosomal recessive pattern
, which means both copies of the gene in each cell must have a pathogenic variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.
Other Names for This Condition
- Hyaline body myopathy
- MYH7-related skeletal myopathy
- Myosin storage congenital myopathy
Additional Information & Resources
Genetic Testing Information
Genetic and Rare Diseases Information Center
Patient Support and Advocacy Resources
Clinical Trials
Catalog of Genes and Diseases from OMIM
Scientific Articles on PubMed
References
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- Dahl-Halvarsson M, Pokrzywa M, Rauthan M, Pilon M, Tajsharghi H. Myosin Storage Myopathy in C. elegans and Human Cultured Muscle Cells. PLoS One. 2017 Jan 26;12(1):e0170613. doi: 10.1371/journal.pone.0170613. eCollection 2017. Citation on PubMed
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- Tajsharghi H, Thornell LE, Lindberg C, Lindvall B, Henriksson KG, Oldfors A. Myosin storage myopathy associated with a heterozygous missense mutation in MYH7. Ann Neurol. 2003 Oct;54(4):494-500. doi: 10.1002/ana.10693. Citation on PubMed
- Viswanathan MC, Tham RC, Kronert WA, Sarsoza F, Trujillo AS, Cammarato A, Bernstein SI. Myosin storage myopathy mutations yield defective myosin filament assembly in vitro and disrupted myofibrillar structure and function in vivo. Hum Mol Genet. 2017 Dec 15;26(24):4799-4813. doi: 10.1093/hmg/ddx359. Citation on PubMed
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