Family history, onset and symptoms
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Q. My grandma had HD and I’m not sure when she got symptoms but probably around her 60s. She twitched a bit but it never went beyond that.
She passed away aged 80 but not from HD. My dad inherited HD from my grandma and the onset was at a roughly similar age, 50s maybe, yet by the time he retired his symptoms were worse than hers, though he is still able to take care of himself (he twitches and reacts more slowly but can otherwise function, walk and eat normally).
I realize I have a 50% chance of getting HD so I would like to know: does my family history give any indication as to 1) possible age of onset and 2) how bad the symptoms might get? Is it realistic to think that, if I have the disease, it will be similar in terms of age of onset and severity as my family?
Michelle, young adult, USA
A. Hi Michelle
Thanks for sending in the question.
In general I don’t think you can predict much about age of onset from what happened in other family members. As far as we can see, there are two different factors governing age of motor onset and progression. The first factor is how long the HD gene is (usually called the CAG repeat number) and the second factor is “other genes”. We now think that there are around 5 other genes that influence age of motor onset. At this stage, we only know that these genes probably exist and their rough whereabouts, but not their exact location or function.
The CAG repeat number can predict age of motor onset in an extremely rough way (it works really well in a statistical model based on thousands of people, but is not useful in predicting what happens in individuals).
So I guess the answer is that you can’t predict the outcome of the illness based on what happened to your relatives