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Huntington's Disease Youth Organization

My Grandmother is at risk. What are my chances?

HDYO has more information about HD available for young people, parents and professionals on our site:

www.hdyo.org

Q. my grandmother is 81 and is at risk for HD. Her father was the first one to have. What are our chances of inheriting it?

Michael, Teen, USA

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A. Hi Michael, Thank you for your email. To answer your question, we need to consider how Huntington’s disease (HD) can be passed on in a family, and how it is caused. As you may know, we all carry two copies of the HD gene, whether or not we are at risk of HD (we inherit one copy from each parent). An individual will develop HD when one copy of the HD gene is larger than usual (called a ‘CAG expansion’). You may find this HDYO article helpful as it goes over this in more detail.

If your grandmother’s father had HD, we would expect that your grandmother would have had a 50% (1 in 2) chance of inheriting the HD gene expansion, when she was born. From what you say, it sounds like your grandmother does not have any signs of HD herself? If she does not have any symptoms, this would be very reassuring, as the longer someone who is at risk lives without developing HD, the lower the chance they inherited the gene expansion (in other words, it would be quite rare for someone who carries an HD gene expansion to have not had any symptoms by the age of 81). If your grandmother does not carry the gene expansion, her children and grandchildren would not have any increased risk of developing HD.

If your grandmother does have the HD gene expansion (which as we said above, seems much less likely given her age), her children would each have had a 50% chance of inheriting it, and grandchildren would start off with a 25% chance (unless their parent develops symptoms or has a genetic test that shows that they carry the gene – in which case the chance would be 50%).

It can often be helpful for family members of someone with HD to see a Genetics doctor or counsellor, as they would be able to look at the family history in more detail and give more specific information about the possible risks, and also could discuss what options would be available to family members, for example in terms of genetic tests.

I hope this helps answer your question, and please do not hesitate to get back to us if you have any other queries.

Best wishes

Bill