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Can you be just a carrier?

June 5, 2016

Huntington's Disease Youth Organization

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Can you be just a carrier?

Q. I was wondering if you could just be a carrier of Huntington’s disease, but still show symptoms or even get the disease?

Gabi, Teen, USA

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A. Dear Gabi,

Thank you for your question.

Someone can’t really just be a carrier of Huntington’s disease (HD) in the same way as in some other genetic conditions. This is because of the way the gene that causes HD is inherited – what is called ‘dominant’ inheritance, and I’ll try my best to explain this briefly below.

As you may know, the HD gene is one of around 23,000 genes that we all carry, and these genes are present in almost all of the cells of our body. The HD gene (like all genes except those on the sex chromosomes) comes as a pair – we inherit one copy of the pair from each parent. So, everyone has two copies of this gene – regardless of whether Huntington’s disease is in the family. HD is caused when one of the pair of genes has a specific change in it (called a ‘CAG expansion’), regardless of whether or not the other copy of the gene is a normal size. This is different to ‘recessive’ genetic conditions like cystic fibrosis, where both copies of a gene must be altered to cause symptoms, whereas if only one copy is altered the individual is usually a healthy carrier.

It isn’t quite that simple though, as in some cases an individual may have an HD gene in an ‘intermediate’ range, where they may not develop symptoms of HD themselves, but their children would be at increased risk (this is pretty uncommon though). Another thing to bear in mind is that the age of onset of symptoms of HD is very variable, so some people who have an expanded HD gene may remain healthy, even relatively late on in life.

I hope this helps answer your question. If you’re interested in reading in more detail about how HD is caused/inherited, you may want to have a look at this HDYO article.

Please do get back to us if you have any other queries, we’re always happy to try to help.

Best wishes