If you suspect that you have HD, you should consult an HD specialist (usually a neurologist) for diagnostic clinical and genetic testing. If you already show symptoms of HD, your doctor will make a diagnosis on the basis of the medical history and clinical findings. The results of this diagnosis are then checked by genetic tests (confirmatory testing). If you do not show any HD symptoms but are at risk because one of your parents has HD, you might be a pre-symptomatic gene carrier. In this case, the HD diagnosis will rely on genetic testing only.

A predictive test is a genetic test to determine whether a person will develop a certain genetic disease. It is by definition performed in a pre-symptomatic stage, i.e. before any signs or symptoms of the disease appear.

Deciding whether to be tested for the HD gene in a pre-symptomatic stage is a personal decision. For some people, the uncertainty of whether they carry the mutant gene is very distressing. But for others, the knowledge that they will develop a fatal disease is even worse.

Living with the knowledge that you are at risk can be very worrying. You may feel that you would prefer to know for certain whether or not you have the abnormal HD gene. At this stage, genetic counselling can be very helpful. Referral to a clinical genetics team ensures that you are provided with accurate and up-to-date information about the disease. It also gives you the opportunity to talk through the choices available to you. Usually you will be offered an appointment with a consultant to discuss your concerns about HD. If you choose to undergo predictive testing to see whether you may have HD in the future, you will be seen several times by the medical team who will guide you through the process. If you decide to have the genetic test, a small blood sample is taken. Depending on the local service, your consultant will disclose your results 2-8 weeks later.

Genetic testing is only provided by genetics specialists or genetics clinics. You can ask your general practitioner to arrange an appointment for you.

The DNA is extracted from blood cells and analysed in a specialised laboratory. Your affected parent’s blood may also be tested to check the original diagnosis of HD.

The genetic test is a DNA test which determines the length of the CAG repeat of the Huntington gene and thus detects the HD mutation. The test can tell whether you carry the HD mutation, but it cannot tell you when the disease itself will start to develop.

There are four different types of results: A result under 27 CAG repeats is unequivocally normal. A repeat length between 27-35 repeats is normal, but there is a small risk that the repeat may increase in future generations. Between 36-39 repeats the result is abnormal, but there is a chance that the person may be affected very late in life or even not at all. Over 40 repeats the gene is unequivocally abnormal.

HD was one of the first inherited genetic disorders for which an accurate genetic test could be performed. The results from the DNA analysis are usually double checked using two separate blood samples.

Yes, the test results are kept confidential and are only disclosed to another person with your written permission.

You need to check with your insurance provider if they cover pre-symptomatic testing. However, before doing so, you should weigh the risks and benefits carefully. It might happen that an insurance company deny health coverage or cancel an existing policy when a person is tested HD positive. Despite the existence of laws which prohibit genetic discrimination by insurers in many countries, unfortunately it does exist in practice. Therefore, you may consider covering the costs of predictive testing by your own.

It depends on the stage of the disease you are and whether your gene status will affect other people. For example, you should tell your spouse or partner that you carry the HD gene. You should also inform your employer once HD starts to affect your job performance. However, you should consider that informing others about your disease may lead to loss of social contacts, discrimination in employment and insurance companies. Before you decide whether, when and whom you tell about HD, you should discuss this with a specialist in legal issues for HD patients.

In the long term, the diagnosis of HD is fatal. The average duration of HD from symptom onset until death is 15-20 years. However, this varies greatly among different individuals and can range from 2 to 43 years.