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.
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
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
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
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.