My grandad has HD - am I at risk?
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Q. “I have just found out about Huntington’s disease being in my family, my granddad has been diagnosed with it at the age of 71. My mom doesn’t know if she has it yet. Am I at risk? If so, can I get tested?” James, 21, USA
A. Hi James,
Thanks for your email. It sounds as though this might be quite new information in the family. I’m not sure whether you and your mom have had a chance to talk about the HD diagnosis in your granddad and what it might mean for both of you? If your granddad is the first person in your family to have been diagnosed with HD, it’s likely that everyone including your mom is trying to get their head around it all. There is a lot of help and support out there and I’d suggest you might find it helpful talking to a genetic counsellor who can look in to the history and give you accurate information.
To come back to your first question whether you could be at risk; yes, Huntington’s disease is a genetic condition that can be passed on in families. Each child of an affected parent has a 50% risk or inheriting the HD gene fault (or to put it another way, an equal chance of not inheriting the HD gene fault). Individuals who have not inherited the gene fault can not in turn pass it on to their children. You can read more about this in the section in HDYO ‘The Huntington’s disease Gene: Under the microscope’. The HD gene fault involves a portion of the gene that is expanded in size. Individuals who have Huntington’s disease usually have a CAG repeat size of >39. The fact that your granddad has only recently been diagnosed with HD at the age of 71 (later than the average age at diagnosis) does make me wonder whether perhaps he does not carry the full expansion (>39 CAG repeats) but that a blood test may have revealed a result in the reduced penetrance range (36-39 CAG repeats). A result in this range is usually associated with a later onset of HD and slower progression. If you are referred for an appointment to a genetic counsellor, they can obtain a copy of the result with your granddad’s consent (some consent forms for genetic testing already include a question re whether information can be used to help other family members) and check the repeat size. It’s important as a first step in order to be able to give you and your mom accurate information. It does also open up the option of predictive testing if that is something you are interested in. I would suggest you take things one step at a time though - perhaps letting your mom know that you would like to look in to things in more detail and find out more about your options. You may then get an idea of how your mom feels about the diagnosis in your granddad and whether predictive testing is something she has thought about for herself. I know it can feel that things are moving too slowly when a diagnosis is first made in a relative, but there really is quite a lot to know about (and more than I can include in an email response). If you have any problems being put in contact with a genetics centre, do let us know.
Rhona Macleod - Genetic Counsellor
Last updated: October 14, 2011 11:39