Description
Myosin storage myopathy is a condition that causes muscle weakness (myopathy) that does not worsen or worsens very slowly over time. This condition is characterized by the formation of protein clumps, which contain a protein called myosin, within certain muscle fibers. The signs and symptoms of myosin storage myopathy usually become noticeable in childhood, although they can occur later. Because of muscle weakness, affected individuals may start walking later than usual and have a waddling gait, trouble climbing stairs, and difficulty lifting the arms above shoulder level. Muscle weakness also causes some affected individuals to have trouble breathing.
Frequency
Myosin storage myopathy is a rare condition. Its prevalence is unknown.
Causes
Mutations in the MYH7 gene cause myosin storage myopathy. The MYH7 gene provides instructions for making a protein known as the cardiac beta (β)-myosin heavy chain. This protein is found in heart (cardiac) muscle and in type I skeletal muscle fibers, one of two types of fibers that make up the muscles that the body uses for movement. Cardiac β-myosin heavy chain is the major component of the thick filament in muscle cell structures called sarcomeres. Sarcomeres, which are made up of thick and thin filaments, are the basic units of muscle contraction. The overlapping thick and thin filaments attach to each other and release, which allows the filaments to move relative to one another so that muscles can contract.
Mutations in the MYH7 gene lead to the production of an altered cardiac β-myosin heavy chain protein, which is thought to be less able to form thick filaments. The altered proteins accumulate in type I skeletal muscle fibers, forming the protein clumps characteristic of the disorder. It is unclear how these changes lead to muscle weakness in people with myosin storage myopathy.
Inheritance
This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.
Other Names for This Condition
- Autosomal dominant hyaline body 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
- Armel TZ, Leinwand LA. Mutations in the beta-myosin rod cause myosin storage myopathy via multiple mechanisms. Proc Natl Acad Sci U S A. 2009 Apr 14;106(15):6291-6. doi: 10.1073/pnas.0900107106. Epub 2009 Mar 31. Citation on PubMed or Free article on PubMed Central
- Pegoraro E, Gavassini BF, Borsato C, Melacini P, Vianello A, Stramare R, Cenacchi G, Angelini C. MYH7 gene mutation in myosin storage myopathy and scapulo-peroneal myopathy. Neuromuscul Disord. 2007 Apr;17(4):321-9. doi: 10.1016/j.nmd.2007.01.010. Epub 2007 Mar 2. Citation on PubMed
- Tajsharghi H, Oldfors A. Myosinopathies: pathology and mechanisms. Acta Neuropathol. 2013 Jan;125(1):3-18. doi: 10.1007/s00401-012-1024-2. Epub 2012 Aug 5. Citation on PubMed or Free article on PubMed Central
- 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
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