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My dad's mum has HD, what are my chances?

May 31, 2015

Huntington's Disease Youth Organization

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


My dad's mum has HD, what are my chances?

Q. My dad’s mum has Huntingtons disease, and that scares me a little, what are the chances I could have those genes and could get the same disease?

Erin, Teen, Australia

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A. Dear Erin,

Thank you for your question. I am sorry to hear that your dad’s mum has HD, and that you are worried about the chance that it could also affect you in the future.

To help answer your question, I need to explain how HD can be inherited. As you may know, HD is caused when there is a specific expansion in the HD gene (in a part of the gene that contains ‘CAG repeats’). When someone with an HD gene expansion has a child, there would usually be a 50% (1 in 2) chance that the child would also carry the HD gene expansion, in which case we would expect them to develop symptoms of HD at some stage in their life. You may find this HDYO article helpful, as it describes how the gene can be passed on in families in more detail.

If your dad did not inherit the HD gene expansion, you would not be at any increased risk of HD. If he did inherit it, then the chance for you would be 50%, as explained above. Combining these two possible scenarios means that, without knowing your dad’s genetic status, the chance that you carry the HD gene expansion would be estimated to be 25% (1 in 4).

I would encourage you to see a genetic counsellor or doctor, who could go over this in more detail, and there may be other information that they could take into account to refine your risks further. They would also be able to give you information about options around genetic testing for you and/or your dad, should you wish. I notice you live in New South Wales, and this website may help you identify your local genetics service.

I wish you all the best with this, and please do not hesitate to get back in touch if you have any further questions, or if you have any difficulty accessing your local genetics service.