10/07/2014 11:30 PM EDT
Source: National Library of Medicine -
Related MedlinePlus Page: Muscle Disorders
Related MedlinePlus Page: Muscle Disorders
Tubular aggregate myopathy
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Reviewed October 2014
What is tubular aggregate myopathy?
Tubular aggregate myopathy is a disorder that primarily affects the skeletal muscles, which are muscles the body uses for movement. This disorder causes muscle pain, cramping, or weakness that begins in childhood and worsens over time. The muscles of the lower limbs are most often affected, although the upper limbs can also be involved. Affected individuals can have difficulty running, climbing stairs, or getting up from a squatting position. The weakness may also lead to an unusual walking style (gait). Some people with this condition develop joint deformities (contractures) in the arms and legs.
Skeletal muscles are normally made up of two types of fibers, called type I and type II fibers, in approximately equal quantities. Type I fibers, also called slow twitch fibers, are used for long, sustained activity, such as walking long distances. Type II fibers, also known as fast twitch fibers, are used for short bursts of strength, which are needed for activities such as running up stairs or sprinting. In people with tubular aggregate myopathy, type II fibers waste away (atrophy), so affected individuals have mostly type I fibers. In addition, proteins build up abnormally in both type I and type II fibers, forming clumps of tube-like structures called tubular aggregates. Tubular aggregates can occur in other muscle disorders, but they are the primary muscle cell abnormality in tubular aggregate myopathy.
How common is tubular aggregate myopathy?
Tubular aggregate myopathy is a rare disorder. Its prevalence is unknown.
What genes are related to tubular aggregate myopathy?
Tubular aggregate myopathy can be caused by mutations in the STIM1 gene. The protein produced from this gene is involved in controlling the entry of positively charged calcium atoms (calcium ions) into cells. The STIM1 protein recognizes when calcium ion levels are low and stimulates the flow of ions into the cell through special channels in the cell membrane called calcium-release activated calcium (CRAC) channels. In muscle cells, the activation of CRAC channels by STIM1 is thought to help replenish calcium stores in a structure called the sarcoplasmic reticulum. STIM1 may also be involved in the release of calcium ions from the sarcoplasmic reticulum. This release of ions stimulates muscle tensing (contraction).
The STIM1 gene mutations involved in tubular aggregate myopathy lead to production of a STIM1 protein that is constantly turned on (constitutively active), which means it continually stimulates calcium ion entry through CRAC channels regardless of ion levels. It is unknown how constitutively active STIM1 leads to the muscle weakness characteristic of tubular aggregate myopathy. Evidence suggests that the tubular aggregates are composed of proteins that are normally part of the sarcoplasmic reticulum. Although the mechanism is unknown, some researchers speculate that the aggregates are the result of uncontrolled calcium levels in muscle cells, possibly due to abnormal STIM1 activity.
Mutations in other genes, some of which have not been identified, are also thought to cause some cases of tubular aggregate myopathy.
Read more about the STIM1 gene.
See a list of genes associated with tubular aggregate myopathy.
How do people inherit tubular aggregate myopathy?
Most cases of tubular aggregate myopathy, including those caused by STIM1 gene mutations, are inherited in an autosomal dominant pattern. Autosomal dominant inheritance means one copy of the altered gene in each cell is sufficient to cause the disorder. In some cases, the mutation is passed through generations in a family. Other cases result from new mutations in the gene and occur in people with no history of the disorder in their family.
Rarely, tubular aggregate myopathy is inherited in an autosomal recessive pattern, which means both copies of a gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. Researchers are still working to determine which gene or genes are associated with autosomal recessive tubular aggregate myopathy.
Where can I find information about diagnosis or management of tubular aggregate myopathy?
These resources address the diagnosis or management of tubular aggregate myopathy and may include treatment providers.
You might also find information on the diagnosis or management of tubular aggregate myopathy inEducational resources and Patient support.
General information about the diagnosis and management of genetic conditions is available in the Handbook. Read more about genetic testing, particularly the difference between clinical tests and research tests.
To locate a healthcare provider, see How can I find a genetics professional in my area? in the Handbook.
Where can I find additional information about tubular aggregate myopathy?
You may find the following resources about tubular aggregate myopathy helpful. These materials are written for the general public.
You may also be interested in these resources, which are designed for healthcare professionals and researchers.
What other names do people use for tubular aggregate myopathy?
- myopathy with tubular aggregates
What if I still have specific questions about tubular aggregate myopathy?
Where can I find general information about genetic conditions?
The Handbook provides basic information about genetics in clear language.
- What does it mean if a disorder seems to run in my family?
- What are the different ways in which a genetic condition can be inherited?
- If a genetic disorder runs in my family, what are the chances that my children will have the condition?
- Why are some genetic conditions more common in particular ethnic groups?
These links provide additional genetics resources that may be useful.
What glossary definitions help with understanding tubular aggregate myopathy?
aggregate ; atrophy ; autosomal ; autosomal dominant ; autosomal recessive ; calcium ; cell ;cell membrane ; contraction ; gait ; gene ; inheritance ; inherited ; ions ; joint ; muscle cell ;muscle cells ; mutation ; prevalence ; protein ; recessive ; sarcoplasmic reticulum
You may find definitions for these and many other terms in the Genetics Home Reference Glossary.
See also Understanding Medical Terminology.
References (7 links)
The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.