Bethlem Myopathy

Diagnosis and Testing

How do I get tested for Bethlem myopathy?

There are multiple ways to be tested for Bethlem myopathy. Bethlem myopathy is typically suspected based off of physical signs and symptoms. These people typically will have proximal muscle weakness (muscle weakness that of or near the torso) and contractures (stiffness of joints causing limited mobility) most commonly of the long fingers, elbows, and ankles. Bethlem myopathy may be tested by blood tests for an enzyme called creatine kinase that leaks from the muscles when muscles are breaking down, muscle MRI, muscle or skin biopsy, or genetic testing. Typically, doctors order the least invasive tests first to look for a diagnosis before ordering more invasive testing.

Creatine kinase levels are usually normal or slightly elevated in people who have Bethlem myopathy. Creatine kinase is an enzyme that leaks from the muscles when they break down. Muscle MRI of the thigh or calf muscles may be performed. For affected individuals, the MRI will show differences in the vasti muscles, which are muscles in the thigh, and the calf muscles. If a muscle biopsy is performed, the results will show what is called myopathic or dystrophic changes. Testing to look specifically for collagen VI in the muscles is typically normal or only slightly abnormal. Testing to look for collagen VI activity on skin cells is typically abnormal and indicates that the person is affected with Bethlem myopathy. Genetic testing can also be performed, which will look for any genetic changes in the COL6A1, COL6A2, and COL6A3 genes.

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More Diagnosis and Testing Content

Is there newborn testing for Bethlem myopathy?

Is there more than one test for Bethlem myopathy?

Who else in my family should have testing for Bethlem myopathy?

What type of sample should be taken for Bethlem myopathy genetic testing?

Is there newborn testing for Bethlem myopathy?

As of February 2019, there is no newborn testing for Bethlem myopathy. Symptoms can be present in infancy so if your doctor suspects a muscle problem in the newborn period, your doctor can order specific tests to look for Bethlem myopathy and other types of muscle disorders.

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Is there more than one test for Bethlem myopathy?

There is more than one test for Bethlem myopathy. Muscle MRI and/or muscle biopsy may be performed and a clinical diagnosis of Bethlem myopathy can be made from those tests. In order to have a genetic diagnosis, genetic testing must be performed. If Bethlem myopathy specifically is suspected, your doctor may order genetic testing and look only at the COL6A1, COL6A2, and COL6A3 genes. Your doctor may also order a panel of genes associated with many different types of muscular dystrophies or whole exome sequencing, which looks at all of the coding genes in our body at the same time. For each of these tests, the lettering of the genes is read and looks for any "misspellings" in the genes. Testing may also be performed that looks for small pieces of the gene that is missing or doubled. Sometimes these misspellings or pieces that are missing or doubled can be damaging to the gene.

If there is someone in your family who is known to have Bethlem myopathy and already had genetic testing, testing can be ordered to look only at the specific genetic variant that was previously found in your family. This way, testing can give you a yes or no answer to see if you also have Bethlem myopathy or not.

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Who else in my family should have testing for Bethlem myopathy?

To determine who else in the family should be tested for Bethlem myopathy, the inheritance pattern must first be known. If Bethlem myopathy is inherited in an autosomal dominant pattern in your family, there is a 50% chance that your parents, siblings, and children are also affected, so they can be tested. If Bethlem myopathy is inherited in an autosomal recessive pattern in your family, there is a 25% chance that your siblings will also have Bethlem myopathy. For autosomal recessive inheritance, it is unlikely that anyone else in the family beside your siblings will be affected unless members of your family tend to have children with people who have a common blood relation. To talk about testing options for Bethlem myopathy in your family, you can consult with a genetic counselor in the United States or Canada or a clinical geneticist.

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What type of sample should be taken for Bethlem myopathy genetic testing?

A blood sample or a saliva sample is typically taken for genetic testing for Bethlem myopathy. The sample will be used to look for any gene changes in the DNA that may be damaging. Your doctor may order a test to look only at the genes responsible for Bethlem myopathy, or a panel of genes that look at many types of muscle disorders. Sometimes when a saliva sample is sent for testing, there is not enough DNA to perform the testing and another sample will be requested.

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