My father was diagnosed but has no family history
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Q. My father was diagnosed about a couple of years ago, my father is 59 and the normal age for symptoms starts around 30-40 years old. No one in his family had Huntington’s. So my question is how could he possibly be diagnosed with HD if it is a genetic disease but yet no one in his family tree ever had it or ever had signs of it?
Stephanie, Young Adult, USA
A. Dear Stephanie,
Many thanks for your question. I am sorry to hear that your father was diagnosed with HD a few years ago, and I can imagine that this would have come as a big shock to the family given that there was no known history of the illness further back in the family.
As you may know, HD is a condition that can run in families, as it is caused by a change in a gene (the type of change is called an ‘expansion’ in a specific part of the genetic code). If you like, you can find a lot more information about this on this HDYO page about the HD gene.
Although in many cases an individual with HD has a parent who also developed the condition, this is not always the case. There are a number of possible explanations how this can happen.
Firstly, the age at which an individual with an HD gene expansion develops symptoms can vary, even within the same family. So, one possibility is that one of your father’s parents carried the HD gene expansion, but did not develop symptoms at the average age (you are completely correct to say the most common age for symptoms to start is around the 40’s, but they can sometimes start much earlier, or much later in life, so some individuals with the expansion may die of something else before HD symptoms develop). Also, in the past, partly because HD was less well known, sometimes people were not diagnosed with HD even if they had symptoms, or the symptoms may have been wrongly called something else (such as Parkinson’s, Alzheimer’s or dementia).
Another possible explanation is that the HD gene expansion happened for the first time in your father (likely very early on in development, before he was born). This is because very occasionally the size of the HD gene can change between a parent and child.
A third possibility is that neither of your father’s parents had HD for non-genetic reasons, for example if he was adopted by them rather than being their ‘biological’ child.
I hope this helps to answer your question, and please do not hesitate to get back in touch if there is anything else we can help with.