Hereditary hemorrhagic telangiectasia

Inheritance

How is hereditary hemorrhagic telangiectasia inherited?

Hereditary hemorrhagic telangiectasia (HHT) is inherited in autosomal dominant manner. This is one way a disorder or trait can be passed down through a family. The first word, "autosomal," means on a chromosome that both males and females carry. Therefore, HHT can affect either gender. The second word, "dominant," means a gene change in one copy of an HHT gene is enough for them to develop the disease. We have two copies of every gene - one from our mother and one from our father - for a dominant condition, only one of them needs to have the problem. This means that if a parent carries an altered ACVRL1, ENG, GDF2, or SMAD4 gene, they have a 50% chance to pass the affected gene to each of their offspring, regardless of gender. This also means that there is a 50% chance that an affected parent would not pass this on to their children.

In rare instances, there is no previous history of HHT in the family. The altered gene occurs randomly, most likely after fertilization. This is also called a de novo mutation. The altered gene in the child can be passed on as an autosomal dominant trait. In families with a child with a de novo mutation, the likelihood of having another child with HHT is extremely low.

If you have a family member with HHT and you would like to know if you are a carrier or learn more about the genetics of the disorder, talk to your doctor or meet with a genetic counselor to discuss testing options.

References
  • Hereditary hemorrhagic telangiectasia. The National Organization for Rare Disorders website. Accessed February 23, 2017. https://rarediseases.org/rare-diseases/hereditary-hemorrhagic-telangiectasia/
  • Hereditary hemorrhagic telangiectasia. Genetics Home Reference website. Accessed February 23, 2017. https://ghr.nlm.nih.gov/condition/hereditary-hemorrhagic-telangiectasia
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How likely is hereditary hemorrhagic telangiectasia to be passed on in a family?

What does it mean to have inherited a "variant" or "variant of unknown significance" in the gene for hereditary hemorrhagic telangiectasia?

How likely is hereditary hemorrhagic telangiectasia to be passed on in a family?

We each get two copies of most of our genes from our parents. One copy comes from our mother and the other copy comes from our father. Hereditary hemorrhagic telangiectasia can be caused by at least four different genes that when altered (mutated) can cause the disorder. These are the ACVRL1, ENG, GDF2, or SMAD4 genes. In HHT, only one parent must pass along a nonworking copy of the altered gene to cause the disorder. Because of this, HHT is inherited in what is called an autosomal dominant pattern. This means a person only needs one altered gene to have the disorder. In most families with HHT, one parent will have an alteration in one of these genes, which causes their disease. So, each of their children will have a 50% chance of inheriting that mutation and developing the disease.

In rare instances, a child will develop HHT and be the first person in the family with the disorder. This occurs because of a de novo mutation, which means that the altered gene occurs randomly, most likely after fertilization. The child who carries the altered gene can pass on the alteration in an autosomal dominant manner. In families with a child with a de novo mutation, the likelihood of having another child with HHT is extremely low.

References
  • Hereditary hemorrhagic telangiectasia. The National Organization for Rare Disorders website. Accessed February 23, 2017. https://rarediseases.org/rare-diseases/hereditary-hemorrhagic-telangiectasia/
  • Hereditary hemorrhagic telangiectasia. Genetics Home Reference website. Accessed February 23, 2017. https://ghr.nlm.nih.gov/condition/hereditary-hemorrhagic-telangiectasia
What does it mean to have inherited a "variant" or "variant of unknown significance" in the gene for hereditary hemorrhagic telangiectasia?

Hereditary hemorrhagic telangiectasia (HHT) is caused by a change (variant) in one of four genes, the ACVRL1, ENG, GDF2, or SMAD4 genes. Not all changes in a gene necessarily cause disease. If a change is known to cause HHT, it is known as a pathogenic or disease-causing variant. Most people with a pathogenic variant in one of these genes eventually develop symptoms of the disorder, but sometimes symptoms may be very mild. Sometimes gene changes are found and scientists are unsure what it means, either because it has not been found before or has only been found in a few people. This is known as a variant of unknown significance. If you have a variant of unknown significance in one of these genes, talk to your doctor about further testing that may help find out whether the gene change is pathogenic or not. A genetic counselor may also be able to help you review your test results. To find a genetic counselor near you who can discuss testing and results, visit the National Society of Genetic Counselors Find a Genetic Counselor website.

References
  • McDonald J, Pyeritz RE. Hereditary Hemorrhagic Telangiectasia. GeneReviews website. Accessed February 23, 2017. https://www.ncbi.nlm.nih.gov/books/NBK1351/

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