DNA and the alphabet soup that causes Huntington’s disease

The science behind Huntington's disease can be tricky to understand

Carlos Briceño avatar

by Carlos Briceño |

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After my wife, Jill, started experiencing symptoms that led her to suspect she had inherited the faulty gene that causes Huntington’s disease (HD), she decided to find out for certain.

When she told me she wanted to have her DNA tested for HD, my first question was, “How will a blood test show you have HD?”

“Good question,” she answered and then picked up her phone to read a long paragraph with several difficult-to-pronounce words that reminded me how scientists love their jargon. The gist was that HD is caused by a greater number than normal of CAG repeats in the HTT gene.

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Jill explained that, years ago, she had emailed herself that information in case our daughter, Alexus, ever wanted to know more about a genetic test.

I told her I appreciated her foresight, but I also wondered what she was talking about because all of those scientific terms were complicated, and frankly, I didn’t understand them.

“Can you please explain all of that in a non-science-y way?”

“Imagine you are looking at a spiral staircase — DNA — with ‘stairs’ that are made up of pairs of four things called bases. The bases stick together two by two, and they are called adenine (A), cytosine (C), guanine (G), and thymine (T). These bases are the code behind all our DNA and genes.

“When scientists look at a gene sequence, they see a type of code. The code might look like this: CCCTACCAGCAGCAGCAGCAG. The gene that causes Huntington’s disease contains a section where the bases C, A, and G are repeated. When they count the number of CAG repeats, anything over 40 is considered gene-positive.”

A layer of complication

I took a moment to think about what she said, and for the most part, I understood. The part I couldn’t stop thinking about was Jill’s statement about having to look it up to explain to our daughter. At some point, Jill realized Alexus may want to understand what a CAG repeat was.

This is the sad truth for families affected by HD. Some knowledge of science is required to deal with the disease, which is another way of saying it adds a layer of complication to the process of finding out if you have it or not.

Jill saw the sad look on my face as I pondered what she must have been thinking about to prepare herself for the possibility of our daughter having HD. To make me feel better, she said, “Being prepared helped me accept that one day Alexus and I may have HD. And I’m glad Alexus was never in denial about talking about it and asking questions.”

As it turned out, Jill and Alexus both took a genetic test and discovered they are gene-positive for this rare disease. As horrible as that knowledge is, they are grateful they now know, which helps them to live life fully each day. It makes us all cognizant of how precious each second is.

Note: Huntington’s Disease News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The opinions expressed in this column are not those of Huntington’s Disease News or its parent company, BioNews, and are intended to spark discussion about issues pertaining to Huntington’s disease.


Michael Boud avatar

Michael Boud

You are going a greet service. I have scores of gene positive in my family

Carlos Briceño avatar

Carlos Briceño

Thank you for reading the column, and I am sorry to hear your family is peppered with the HD Cag repeat. I will keep you all in my thoughts and prayers.


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