Bethlem Myopathy

Inheritance

How is Bethlem myopathy inherited?

Bethlem myopathy is usually inherited in an autosomal dominant pattern. We have two copies of the genes that cause Bethlem myopathy; one from our mother and one from our father. Autosomal dominant inheritance means that if an individual has a genetic change in one copy of the gene that is enough to show symptoms and have the condition. For individuals who have autosomal dominant Bethlem myopathy, there would be a 50% chance to have a child with Bethlem myopathy in each pregnancy.

Sometimes, Bethlem myopathy can be inherited in an autosomal recessive pattern. Autosomal recessive inheritance means that an individual must have a genetic change in both copies of the gene in order to have the condition. Their parents would only have one genetic change and have not been reported to have symptoms. For these families, the unaffected parents would be called carriers. When two parents are carriers for autosomal recessive Bethlem myopathy, there is a 25% chance to have a child with Bethlem myopathy in each pregnancy.

References
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What does it mean to have a variant of uncertain significance in the gene for Bethlem myopathy?

Can my child still have Bethlem myopathy without having a gene mutation?

Can my child have Bethlem myopathy if neither parent has Bethlem myopathy?

If I have Bethlem myopathy, will my children have it?

Are there any forms of Bethlem myopathy that are not genetic?

What does it mean to have a variant of uncertain significance in the gene for Bethlem myopathy?

A variant of uncertain significance in one of the genes for Bethlem myopathy means that a change in the DNA was identified that was different from what is expected, but it is unknown at the time if the DNA change is damaging to the gene, or if it is a normal variation. The genetic change most likely has never been seen before, so it is unknown how it affects the gene. When variants of uncertain significance are identified, it is not recommended to test other family members to see if they are also affected with Bethlem myopathy because the variant may not actually be disease causing.

When variants of uncertain significance are identified, your doctor may do testing on other family members to figure out the significance. Over time, the variant may be reclassified as a normal variation or a disease causing variant as new information becomes available. You can consult with a genetic counselor to help understand the significance of your test results. Genetic counselors in Canada can be found at the Canadian Association of Genetic Counselors website.

References
Can my child still have Bethlem myopathy without having a gene mutation?

It is possible for your child to have Bethlem myopathy without having an identifiable gene mutation. About 66% of people who have Bethlem myopathy based on physical signs and symptoms have an identifiable gene mutation. That means that about 34% of people who have Bethlem myopathy based on clinical signs and symptoms do not have an identifiable gene mutation. If your child's testing does not reveal a disease causing gene mutation, it may be due to the limitations in current technology.

References
Can my child have Bethlem myopathy if neither parent has Bethlem myopathy?

It is possible for your child to be the first one in the family with Bethlem myopathy. If autosomal dominant inheritance is established in your child, your child can have a de novo or new gene mutation in one of the genes for Bethlem myopathy. These new genetic changes happen all of the time and are a normal part of biology. We all have new genetic mutations, which make us not exactly like our parents.

If autosomal recessive inheritance is established in your child, you and your partner are likely carriers for Bethlem myopathy. Carriers of Bethlem myopathy typically do not have symptoms. The chance for two carriers of Bethlem myopathy to have a child with Bethlem myopathy is 25% for each pregnancy.

References
  • Lampe AK, Flanigan KM, Bushby KM, et al. Collagen Type VI-Related Disorders. 2004 Jun 25 [Updated 2012 Aug 9]. In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2019.Available from: https://www.ncbi.nlm.nih.gov/books/NBK1503/
  • Online Mendelian Inheritance in Man, OMIM®. Johns Hopkins University, Baltimore, MD. MIM Number: 158810: October 4, 2018: https://omim.org/entry/158810 Accessed 21FEB19
If I have Bethlem myopathy, will my children have it?

If you have Bethlem myopathy that is inherited in an autosomal dominant pattern (i.e. there was one disease causing variant identified that is thought to be sufficient to cause disease), there will be a 50% chance for each of you children to inherit the genetic variant for Bethlem myopathy.

If you have Bethlem myopathy that is inherited in an autosomal recessive pattern (ie. there were two disease causing variants identified that are thought to be causing disease), the chance for you to have a child with Bethlem myopathy is very low. Your partner should have carrier screening for Bethlem myopathy to see if they are a carrier. If your partner is not a carrier, your children will only be carriers; they would not be affected. If you partner is a carrier, there would be a 50% chance to have a child with Bethlem myopathy.

You can consult with a genetic counselor to learn all about your screening and reproductive planning options. In the United States, you can find a genetic counselor through the National Society of Genetic Counselors. Genetic counselors in Canada can be found at the Canadian Association of Genetic Counselors website.

References
Are there any forms of Bethlem myopathy that are not genetic?

There are no forms of Bethlem myopathy that are not genetic. There are some muscles conditions though that are not genetic and can be acquired. You can consult with a clinical geneticist for a complete evaluation if you are unsure of your diagnosis. You can find a clinical geneticist in the United States through the American College of Medical Genetics and Genomics.

References

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