If you have features of Huntington's disease, your GP will refer you to a clinician with specialist expertise in the condition if they feel further investigation is needed.
Many areas have Huntington's disease management clinics with a range of specialists, including a neurologist (a doctor who specialises in conditions that affect the brain and spinal cord).
The specialist will ask about your symptoms, such as whether you've had recent emotional problems, to see if it's likely you have Huntington's disease and to rule out similar conditions.
They may also examine you and test your thinking, eye movements, balance, walking, and whether you have any involuntary movements, such as chorea (fidgety or jerky movements).
Confirming the diagnosis
People with Huntington's disease often start to experience symptoms a number of years before the condition is actually diagnosed. This is particularly true in cases where someone is unaware that the condition runs in their family.
If you're showing features of Huntington's disease and it's known to run in your family, or if your doctor strongly suspects that you have the condition, genetic testing can be carried out to confirm the diagnosis.
It's important to realise that the diagnosis is based on the doctor recognising a combination of a number of factors – neurological examination, family history and genetic testing. It's possible to have the gene change and still be healthy. This is known as "premanifest Huntington's disease".
The children of someone with Huntington's disease can take a genetic test after the age of 18 to see whether they've inherited the faulty gene. If they've inherited the faulty gene, they'll develop Huntington's disease, but it's not possible to work out at what age.
You can ask your GP or neurologist to arrange an appointment for you at a regional genetic clinic. You'll receive some counselling and then blood samples will be taken. Your DNA will be extracted from the blood samples and analysed to see whether you have inherited the faulty gene.
You may have to wait two to four weeks for the test results.
In the early stages of Huntington's disease, there may not be any specific changes on the brain scan. A doctor may use a brain scan at any stage of the illness if they're concerned there may be other problems in addition to Huntington's disease.
A brain scan may involve having a computerised tomography (CT scan) or a magnetic resonance imaging (MRI) scan. An MRI scan is more detailed and is more sensitive at picking up changes in the brain. However, it's a more claustrophobic procedure.
Getting tested in pregnancy
If you're pregnant and already known to have the Huntington's disease gene, it's possible to have a direct test on the pregnancy at 11 weeks. This needs careful consideration and can be discussed with a genetic counselling team.
If one half of a couple is at risk of Huntington's disease, but doesn't want to find out whether they have the condition, and the couple would like to have children free of risk, more complex indirect genetic testing is needed. This needs to be discussed with the genetic clinic. One option is preimplantation genetic diagnosis (see below).
Preimplantation genetic diagnosis
Preimplantation genetic diagnosis can be used when one partner is known to have the faulty gene. This is a direct test.
It involves having in vitro fertilisation (IVF) treatment, then genetically testing the embryo in a laboratory to see if it has the faulty gene. The embryo will only be placed inside the woman if it doesn't have the faulty gene and there's no risk of the baby developing Huntington's disease.
Preimplantation genetic diagnosis isn't a straightforward procedure, and raises a number of issues that need to be considered in detail.
The Human Fertilisation and Embryology Authority (HFEA) has more information about preimplantation genetic diagnosis.
Should I get tested?
Not everyone wants to know if they've inherited the faulty gene associated with Huntington's disease. It's a personal choice.
Some people say they would rather not know because they want to enjoy their life and they may die of other causes before the condition develops.
Most people have approximately 40 years of a normal healthy life before the condition develops.
Less than one in five people at risk of Huntington's disease choose to have the genetic test.
If you're considering genetic testing, it's strongly recommended that you speak to a genetic counsellor first. Your GP can refer you.
The Huntington's Disease Association website has more information about predictive testing for Huntington's disease.