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Cap Myopathy

Last updated May 5, 2018

Approved by: Krish Tangella MD, MBA, FCAP

Cap Myopathy is a disorder that primarily affects skeletal muscles, the muscles that the body uses for movement. The name Cap Myopathy comes from characteristic abnormal cap-like structures that can be seen in muscle cells when muscle tissue is viewed under a microscope.


What are the other Names for this Condition? (Also known as/Synonyms)

  • Cap Disease
  • Congenital Myopathy with Caps

What is Cap Myopathy? (Definition/Background Information)

  • Cap Myopathy is a disorder that primarily affects skeletal muscles, the muscles that the body uses for movement. The name Cap Myopathy comes from characteristic abnormal cap-like structures that can be seen in muscle cells when muscle tissue is viewed under a microscope
  • People with Cap Myopathy have muscle weakness (myopathy) and poor muscle tone (hypotonia) throughout the body, but they are most severely affected in the muscles of the face, neck, and limbs. The muscle weakness, which begins at birth or during childhood, can worsen over time
  • Cap Myopathy can be caused by mutations in the ACTA1, TPM2, or TPM3 genes. This condition follows an autosomal dominant manner of inheritance, however, most cases are not inherited; they result from new mutations in the gene and occur in people with no history of the disorder in their family
  • The severity of Cap Myopathy is related to the percentage of muscle cells that have these caps. Individuals in whom 70-75% of muscle cells have caps typically have severe breathing problems and may not survive childhood, while those in whom 10-30% of muscle cells have caps have milder symptoms and can live into adulthood

(Source: Cap Myopathy; Genetic and Rare Disease Information Center (GARD) of National Center for Advancing Translational Science (NCATS), USA.)

Who gets Cap Myopathy? (Age and Sex Distribution)

  • Cap Myopathy is a rare congenital disorder. The presentation of symptoms may occur at birth or during childhood
  • Both males and females may be affected
  • Worldwide, individuals of all racial and ethnic groups may be affected

What are the Risk Factors for Cap Myopathy? (Predisposing Factors)

  • A positive family history may be an important risk factor, since Cap Myopathy can be inherited
  • Currently, no other risk factors have been clearly identified for the condition

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Cap Myopathy? (Etiology)

  • Cap Myopathy can be caused by mutations in the ACTA1, TPM2, or TPM3 genes
  • This condition follows an autosomal dominant manner of inheritance, however, most cases are not inherited; they result from new mutations in the gene and occur in people with no history of the disorder in their family

(Source: Cap Myopathy; Genetic and Rare Disease Information Center (GARD) of National Center for Advancing Translational Science (NCATS), USA.)

Autosomal dominant: Autosomal dominant conditions are traits or disorders that are present when only one copy of the mutation is inherited on a non-sex chromosome. In these types of conditions, the individual has one normal copy and one mutant copy of the gene. The abnormal gene dominates, masking the effects of the correctly function gene. If an individual has an autosomal dominant condition, the chance of passing the abnormal gene on to their offspring is 50%. Children, who do not inherit the abnormal gene, will not develop the condition or pass it on to their offspring.

What are the Signs and Symptoms of Cap Myopathy?

The signs and symptoms of Cap Myopathy may vary in severity among affected individuals, and include the following:

  • Poor muscle tone (hypotonia)
  • Muscle weakness in face, neck and limbs

(Source: Cap Myopathy; Genetic and Rare Disease Information Center (GARD) of National Center for Advancing Translational Science (NCATS), USA.)

  • Drooping eyelids
  • High-arched palate
  • Swallowing difficulties
  • Delay in reaching developmental milestones, such as sitting, crawling, walking or running
  • Lordosis, scoliosis
  • Breathing difficulties
  • Tiring easily with mild exertion

How is Cap Myopathy Diagnosed?

Cap Myopathy is diagnosed on the basis of the following information:

  • Complete physical examination
  • Thorough medical history evaluation
  • Assessment of signs and symptoms
  • Laboratory tests
  • Imaging studies
  • Biopsy studies, if necessary

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Cap Myopathy?

The complications of Cap Myopathy may include:

  • Inadequate weight gain due to swallowing difficulties
  • Risk of falls
  • Breathing distress
  • Severe back pain due to spine abnormalities such as lordosis and scoliosis
  • Crowding of organs in the chest cavity, leading to abnormalities in heart and lung function
  • Progressive worsening of muscle weakness

Complications may occur with or without treatment, and in some cases, due to treatment also.

How is Cap Myopathy Treated?

There is no cure for Cap Myopathy, since it is a genetic condition. The treatment is usually given to manage the signs and symptoms and any complication that develops.

How can Cap Myopathy be Prevented?

Cap Myopathy may not be preventable, since it is a genetic disorder.

  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy), if available, may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders
  • Regular medical screening at periodic intervals with tests and physical examinations are recommended

What is the Prognosis of Cap Myopathy? (Outcomes/Resolutions)

  • The prognosis of Cap Myopathy is dependent upon the severity of the signs and symptoms and associated complications, if any
  • The severity of Cap Myopathy is related to the percentage of muscle cells that have these caps. Individuals in whom 70-75% of muscle cells have caps typically have severe breathing problems and may not survive childhood, while those in whom 10-30% of muscle cells have caps have milder symptoms and can live into adulthood

(Source: Cap Myopathy; Genetic and Rare Disease Information Center (GARD) of National Center for Advancing Translational Science (NCATS), USA.)

Additional and Relevant Useful Information for Cap Myopathy:

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/rare-disorders/

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Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: May 5, 2018
Last updated: May 5, 2018