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Genetic Testing

February 18, 2022

Huntington's Disease Youth Organization

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In 1993, scientists discovered exactly where the gene which causes Huntington's disease is located in our DNA and figured out what it was doing. Because of this people are now able to have what is called a 'predictive test'. It is known as a predictive test because the test can be taken by people at risk of Huntington's disease who currently show no symptoms and want to learn whether they will develop the condition in the future. The result of this test will usually be able to tell a person whether they have the expanded gene or not.

It is important to note that if a person already has symptoms but has not been diagnosed, then a different approach would be taken which is known as 'symptomatic testing'. This would involve that person going through a series of assessments with a doctor to confirm a diagnosis of Huntington's disease and is quite different to 'Predictive Testing', which is what we are focusing on in this section.

The science behind testing

You may hear people say that they 'have the gene' when referring to themselves as having Huntington's disease. But the truth is all humans have the gene that may cause Huntington's disease - even those who never develop the condition. So if we all have the gene, why do some develop Huntington's disease when others do not? The difference is people who develop symptoms of Huntington's disease have a larger expansion of the gene than normal.

What is this gene expansion?

CAG repeats

Without getting too scientific (which is hard as we are discussing DNA!), there is a section, in the gene, which repeats itself over and over again. This is known as a 'CAG repeat' and each individual has a different amount of repeats. However, people with Huntington's disease tend to have more repeats than usual, which means that the gene expands more than it should. This expansion can lead to Huntington's disease.

The reason we are explaining CAG repeats is because of their relevance to predictive testing for Huntington's disease. When people at-risk for Huntington's disease have a predictive test, that person's DNA is sent to a lab, and the clinical scientists will use special machines and lab techniques that will count how many CAG repeats that person has in the gene specific to Huntington's disease. Once they know how many repeats a person has, they can tell if they will get the disease or not.

How many CAG repeats will cause Huntington's disease?

CAG repeats are split into four categories. If a person has less than 27 CAG repeats then they are what is called, 'negative' - meaning they will not get Huntington's disease and they are not at risk of passing the disease onto any children that person has.

Someone who has 40 CAG repeats or more will definitely develop symptoms of Huntington's disease in their lifetime (although it is not possible to say when symptoms will start) and the risk to any children is 50%.

If a person has between 27-35 CAG repeats, they will not develop Huntington's disease, but there will still be a very small risk of that person passing on the disease to any children (the risk is about 5%).

Whereas somebody who has a CAG repeat between 36-39, would be in what is sometimes called the 'grey area', because it is uncertain whether they will develop symptoms in their lifetime or not.

Less than 27 CAG repeats

Negative - will not develop Huntington's disease and children not at risk

27-35 CAG repeats

Negative - will not develop the disease but small risk to children.

36-39 CAG repeats

Positive - but may develop symptoms at an older age. 50% risk to children.

40+ CAG repeats

Positive - will develop symptoms in your lifetime. 50% risk to children.

Technically people in the 36-39 CAG repeat range do have the expanded gene, but people in this range may develop symptoms of Huntington's disease at an older age. However, the risk of passing the expanded gene onto any children is 50%.

If you have been tested it is always important to be clear about the result of your predictive test. If you have any questions, or do not understand what the result has shown, do go back to the clinician who arranged your test.

Genetic counselling and the testing process

As you have read above, testing is ultimately about finding out your CAG repeat - and this can be done with a blood test. But taking a predictive test in order to find out whether you will get Huntington's disease or not is a huge decision to make in one's life, and an enormous thing to deal with emotionally. What if a person gets a positive result? Would they be able to cope? Can they live positively with this news? These are questions that have to be asked, and that is why, before anybody can have a predictive test for Huntington's disease, they should undergo genetic counselling. How long the counselling takes depends on you and your counsellor, and your particular personal circumstances but generally it can take anything from 2-6 months. In that time many things are discussed, as one Genetic Counsellor explains:

'It's very much a two way process whereby you can explore the option of a predictive test and what it entails, including the possible test outcomes. There may be discussions around alternatives to testing, possible impact on other family members and the question of timing of the test. It can vary how ready an individual feels to proceed with a test - and that's fine - we'd want to take it at a pace that feels right for the individual.' Tiffany, Genetic Counsellor

To begin the testing process you usually need to speak with your doctor, who will then put you in contact with your local genetics department. In order to be tested you normally have to be at least 18 years old - although if you are under 18, you can still speak with a genetic counsellor about what a test involves and any other issues you may have with regards to Huntington's disease.

If at any stage during the counselling process you change your mind and do not want to be tested, you can stop the process straight away. Some people even get all the way to having their blood taken and decide now is not the right time for them to hear their results, so they ask for their results to be kept under lock and key until they feel ready to collect them. The doctors and genetic counsellors will not read your results until you've decided to receive the news.

It is your choice

It is very important to remember that testing is a personal choice - a choice only you have the right to make. Some people in your life may tell you to test or not to test. But it is not up to them at all - it is entirely your decision and you should only get tested if you are sure this is what you want.

'I haven't set a date on when I'll test, but I want it to be on my terms and not on other people's terms. I've encountered people in my life who have pressured me to test and not test. After the countless words from people, I finally realised it is not up to them and I have to feel it in my heart when the time is right.' Stacey

There is no right or wrong answer when it comes to making a decision about testing. People are different! We all live different lives and we all make different decisions. Some will choose to test (& will vary at what stage in their life they choose to do so), others will not - there are perfectly good reasons for deciding one way or the other. Although it is your decision, you may also wish to discuss your feelings with those closest to you (like a partner) for whom the result will also have a bearing. But ultimately it is your choice.


If you decide that you want to be tested and feel now is the right time for you, then it is important to be prepared. One of the main practical things you may wish to do before you get your test result, is to get life insurance, as you may experience higher premiums if you seek insurance after you have tested (positive). Whereas if you already have insurance before you test, then you do not need to disclose your test results to insurers and your results will not affect your existing insurance. Issues with insurance vary depending on where you are and which country you are in. If you do not have insurance and want to get some before you test - then you can talk with your genetic counsellor or your national Huntington's disease organisation about this issue.

Young people tend not to think about things like insurance, it is usually something people look into when they are buying a house or starting a family etc. But insurance is actually very important and should not be overlooked.

'I got tested when I was 19 and although I knew about insurance, I was too young to really understand how important it was to have insurance in place. So I just pushed it to one side and focused on the testing process. Now, some years later, I do wish that I had taken out insurance.' Joel

It is your choice, you do not need to be insured in order to test - it is not a requirement, but it would benefit you in the long run to look into it.

Emotional aspects of the testing process

Aside from the practical ways to be prepared, testing is also a very emotional process from start to finish. From making the decision to test, going to your genetic counselling sessions, having your blood taken and receiving your result - each stage provides its own emotional hurdles to overcome.


Dealing with the emotions of testing is incredibly challenging for anyone. When you take into account that the whole process can take months, it can become very difficult for a person to maintain their calm throughout. You may have many ups and downs during the process, don't be alarmed by this, it is quite normal and you should keep discussing your emotions with the genetic counsellor (that is what they are there for). You could also seek advice from others who have gone through the testing process for Huntington's disease already and have faced the same emotions and difficulties.

The waiting period

There is a part of the testing process that has not been highlighted yet, 'the waiting period'. This period covers the time between having your blood sample taken and receiving your test results. People have to wait for weeks in-between their blood being taken and their test results appointment. Just how long that wait is depends on where you live and the clinic you are using. But this can be an incredibly difficult time for a person in the testing process; those weeks can often feel like months! People can become very anxious during the waiting period and it is important to try and stay busy during this time.

'When I say that the weeks between getting my blood drawn and getting my results were agonising, I mean it. I believe those were the hardest weeks of my life. Every day, it was a battle of thoughts going through my head, making it hard to sleep. How do you deal with such an internal battle? You are literally driving yourself crazy, an emotional wreck, getting no sleep because your mind is racing, and scared that at the moment, you don't know what your future holds.' Laura

If you feel it would be helpful to speak to your genetic counsellor during this period do call them (they will not know your result at this stage). Or again, seek advice and support from those who have experienced the waiting period themselves - this can be quite comforting.

Preparing for your results

Preparing for results is another challenging aspect of the testing process. Many people tend to develop a 'feeling' one way or the other about whether they are going to test positive or negative. Obviously you can't guess or 'feel' what result you are going to get, and these guesses can end up causing more shock when you receive your results (should you get the result you weren't expecting). It can often be good just to remind yourself during the process that until you test you are 'at-risk', rather than trying to guess one way or the other.

'I spent the entire testing process feeling that I was going to test negative. When I got my results, and they were positive... it was pretty tough to take. It took me at least a few months to move on from there.' Joe

However, preparing for your results can be useful and during your counselling you may be asked to think about what you will do if you test positive or negative. This is a good exercise because it allows you to really think and plan how you will react to your results, whatever they may be.


Support during the testing process is not only important but can be very comforting. You are entitled and encouraged to bring along a family member or a friend to both your counselling sessions and your results appointment - and it is highly advised that you do so. Some people, when they decide to get tested, are hesitant to tell their family/friends, and decide to face the process alone. People's reasons for not telling their family about such a huge life decision are usually because they do not want to put their loved ones through any extra stress, worry or pain - people want to protect their family. It is an understandable reason for keeping the process quiet; after all, many people testing have families that are already dealing with Huntington's disease and people often feel like they are burdening their family by adding the testing process to the list of things to cope with. But it is unlikely to help you in the long run to keep this to yourself. As has been highlighted, testing is an incredibly emotional journey - you will need support during this process. Do not face it alone if there is no reason to - this is hopefully a time for the family to all get behind the person testing and support each other.

For people testing who have siblings either at-risk, already tested or symptomatic, testing can be an even tougher experience. Imagine testing negative if one of your siblings had already tested positive - how do you tell them your news? This is often called 'sibling guilt' and it can be uncomfortable and difficult to handle. But it does not have to be, as one family highlights:

'Telling my siblings was emotionally complex. I desperately wished they could have had the same result. It seemed so unfair how the disease picks and chooses whom it will take, and whom it will leave behind to witness the devastating effects. But as I rang each one of my wonderful brothers, they were thrilled and cheered down the phone.' Jen, as she tells her brothers (both of whom are positive) she has tested negative.

Support is the key, whatever the results as siblings you should use this as an opportunity to become closer and even more supportive. Talk about the worries you have with your siblings, express your concerns about how the family will react to your results before you get them - be prepared as a family.

However, you shouldn't feel that you need your family's permission or support to get tested - remember, it is your choice. There are other sources of support for you that you can reach through your national Huntington's disease organisation, your genetic counsellor and HDYO. Having contact with other young people that have been through testing can be an excellent source of support during the testing process and that is a support option that you may find on the our Facebook Group.

Getting your results

Positive or negative, the day you receive your result may feel like the most surreal day of your life and it is important that you take the time to accept your result. The process of acceptance can only be done gradually over time. Both results will bring with them different emotions and different hurdles in the future. Testing positive raises some more obvious issues, but testing negative also has its complications for people. Both are discussed in the sections below.

Testing Positive

Testing positive for Huntington's disease is often a traumatic experience - one that can really knock you off your feet. Do not be surprised if it takes you many months to feel like yourself again, these things do take time and it is important not to expect too much from yourself after your result. As was highlighted in the main testing section, accepting your results can only be done gradually over time.

'When I tested positive I must have spent the next 6 months feeling down and sorry for myself - I was not very productive during that time! But I was always looking to move forwards and accept my results, and gradually I started to make progress. Now, 3 years later, I am very happy with my life and have accepted my results.' Ben

It is important to remember that you are able to have follow-up appointments with your genetic counsellor anytime you want to discuss your result and how you feel. This can be very useful and the counsellor will be happy to go through any issues that are on your mind.

You also need to think about who you are going to inform about your results. Telling friends or work colleagues is really only something you can decide upon. The lack of understanding about the disease can cause issues, will they understand? Will it affect how people view you at work? Etc.

However, once you have had time to get used to the result, you can use the fact you have tested positive as the reason/motivation to do the things in life that you have always wanted to do. Why not go travelling, or change your career, begin a new fitness regime or have a fresh new start in life! Testing positive can be great motivation to get out there and experience life. Again, it may take time to find that motivation, but once you have it you can really make the most of things.

Another important issue to remember is that testing positive may change the way you see things in life. For instance, if you have a family member who is symptomatic with Huntington's disease, you may find that, because you have tested positive, it is hard for you to witness that person's progression. As one young man explains:

'After I tested positive it became really hard for me to care for my father who had Huntington's disease. I kept looking at him with his symptoms, and thinking "that will be me in 20 years". It was really difficult to deal with at first, but after a while I settled down again and things got back to normal.' John

Time really does help, and you may not feel like you have a lot of it right now, but be assured you still have plenty of time to enjoy life. Research into Huntington's disease is progressing really quickly and there is very much real hope for the future. You may want to help by participating in research yourself, it can be a very rewarding experience and many feel they are being productive by participating in research studies. Click here to find out more about how you can help with research.

There are many good days yet to experience, and yes, you will have your bad days too (who doesn't). But stay positive and keep moving forwards and you shall continue to achieve in life. Remember that you have always had the expanded gene; the only difference is that you know this now. You have the advantage of future knowledge about your life, use it. Testing positive might just be the motivation you needed to achieve great things and to lead a life to be proud of.

Testing Negative

Testing negative is generally seen as the 'good result', but people can be too quick to congratulate you on testing negative. They may expect you to be happy, delighted, or ecstatic. When in fact, testing negative does not mean somebody is completely free of Huntington's disease from their lives. The chances are you still have family members who are either symptomatic, at-risk or gene positive - so the worry still remains.

One of the biggest issues for those that test negative is the guilt. So many people feel huge amounts of guilt for receiving a negative result - you may be feeling that way too. It is important that you discuss these feelings with your family and friends, be open and honest - you have every right to highlight your feelings.

'I received a negative result and the biggest feeling I felt was a huge amount of guilt. Some people may think I was selfish not showing that I was happy with this result, but knowing many people who tested positive and having an untested brother, all I could feel was sheer guilt. It is important to speak to friends and family about the result, my father encouraged me to celebrate the negative result, however I felt I could not do that. I suffered with receiving a negative result for months as personally it was a huge mental obstacle for me. It wasn't until I sought deeper advice that I understood that receiving a negative result is nothing to be ashamed about. It is important still however to continue being a part of the Huntington's disease community and supporting others dealing with the struggles of the disease.' Lisa

Some people feel like a part of them has been taken away when they test negative - as if Huntington's disease was a part of their identity, and now it has gone they are unsure what they want to do in life. Feeling this way may cause issues. For instance, one of the main things, for so many years, a person has in common with their family is Huntington's disease, so if someone tests negative and now knows they won't have the condition, they may feel a form of separation from their family - like they have lost that connection.

It is very important that you discuss any issues you are worried about. You are entitled to have follow-up appointments with your genetic counsellor to talk about your result and any issues you have. But as was highlighted before, discuss your feelings with your family as well - they may not realise how you are feeling inside. You can only support each other if you understand the reason why support is needed - that means you need to be open and honest about your feelings with regards to testing negative, do not keep them hidden away purely because you got a 'good result' and feel you should not be complaining.

'Testing negative was without a doubt, the most incredible news I've ever received. The day I received my results was surreal - and a gigantic emotional roller-coaster. What started as the happiest day of my life turned into the hardest night...I was prepared to feel some guilt, but wasn't ready to be completely overwhelmed. I knew logically that I shouldn't feel guilty, but it hit me...HARD! I couldn't get over the fact that I was, for lack of a better term, 'safe'...and the guilt that came with that realization was incredible. I felt so horrible knowing that so many people I love aren't as lucky as I am, or their future was still up in the air. The fear of telling other people sent me into panic attacks and it took everything I had just to keep breathing. Thankfully, I have people in my life who were more supportive than ever, and gave me the exact message I needed to hear: 'That guilt will become a good thing and make you more inspired than ever to make a difference'. Slowly but surely I began to feel like myself again...and even though I still feel guilty some days, I just take it one day at a time and try to keep doing everything I can to contribute to the fight against Huntington's disease!' Elaine

Finally, even though you may have tested negative, you can still help with the search for the cure. There are research studies that want and need people who have tested negative. You can participate in these and do your bit to help not only your family, but others suffering with Huntington's disease too. Check out the research section to learn more.

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