My aunt has HD, is there I chance I do?
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Q. Hi! I have an aunt who was diagnosed with HD a couple of years back. Neither my grandmother, my grandfather (both over 75 y/o) or my mother (55 y/o) are showing any symptoms and as far as any of us know, there haven’t been any other known cases in my family. Could my aunt still have inherited it from my grandparents, and is there still a chance I’m at risk of developing HD?
Mirjam, Young Adult, Norway
A. Hi Mirjam,
Many thanks for contacting us with your question. When there is only one person affected with HD in a family, it can sometimes be more difficult to assess what the risks are for other family members.
There are several possible explanations for the pattern you describe in your family. Given that your grandparents are still well into their late 70’s, perhaps the most likely explanation is that your aunt did not inherit it from either of your grandparents – i.e. the gene change that causes HD happened for the first time in her (likely around the time she was conceived). It may be that one of your grandparents carries an ‘intermediate’ size HD gene, which would not cause HD in them but would mean their children would have been at increased risk of having HD. (This is because the gene can occasionally change in size between a parent and child.) You can read more about the different sized HD genes
Another, probably smaller possibility is that one of your grandparents does carry the gene change that causes HD, but has not developed symptoms. The reason we could not completely rule this out (unless they have had a genetic test) is that the age at which someone who carries the HD gene starts to have symptoms can be quite variable. The average age is around 35-50, but a minority of individuals with HD have symptoms much earlier, or much later in life than this. If one of your grandparents does have it, your mother would have had a 1 in 2 chance of inheriting it when she was born, and in that situation your current chance would be (at most) 1 in 4.
As this situation is not straightforward, I would encourage you/your family to consider seeing a Genetic Counsellor or Doctor, who could look at all the information about your family in more detail to hopefully give you a more definite answer, as well as to talk about the options available. Overall though, it is definitely reassuring that your grandparents and mother have not had any symptoms at their current ages.
Please do not hesitate to get back to us if you do have any queries.