Genetic testing for dementia

There are genetic tests that may be useful for people affected by dementia. Read more about genetic testing for dementia – what it involves, what it can help with and when it is covered on the NHS.

Genetics of dementia
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Is there a genetic test for dementia?

Yes. It is possible to be tested for single-gene changes and some of the risk variants linked to dementia. However, genetic testing for dementia is not always appropriate.

When is genetic testing for dementia appropriate?

In some cases, it may seem likely that a person’s dementia is caused by a single-gene change – for example, if the person has a very strong family history of dementia. In these cases, it may be appropriate to offer genetic testing to the person and to their family.

However in most families dementia will not be caused by a single-gene change. In these cases, genetic testing will not be appropriate. This is because testing for risk variants (like APOE4) does not provide any certainty about the person’s chances of developing dementia.

Genetic testing for single-gene changes that cause dementia

Genetic testing for single-gene causes of dementia is available through the NHS.

There are two different types of genetic testing – diagnostic testing and predictive testing. These are used for different purposes.

People affected by dementia can also use genetic testing for family planning.

What is the purpose of diagnostic testing?

A diagnostic genetic test is for a person whose dementia is thought to be caused by a single-gene change.

What are the benefits of diagnostic testing?

Diagnostic testing for dementia can be helpful in several ways:

  • It can provide certainty about the person’s diagnosis. This may then help the person and their family to come to terms with the diagnosis and allow them to plan for the future.
  • It can help them decide if they want to have children and, if so, how they might avoid passing the disease on.
  • It makes it possible for members of the person’s family to have predictive testing if they want to.

How is a diagnostic genetic test done?

Diagnostic testing is usually carried out as part of an assessment in a clinic – for example, a memory clinic. The test usually involves taking a blood sample.

Who can take a diagnostic genetic test?

To see whether genetic testing might be useful, the doctor will collect information on the person’s medical history and that of their close family. If possible, the doctor will collect information on at least three generations of the family. The medical history will include details of:

  • any family members diagnosed with dementia
  • any family history of mental illness (such as schizophrenia or bipolar disorder)
  • any family history of strokes or neurological conditions (such as Parkinson’s disease or motor neurone disease).

Diagnostic testing for familial dementia is only normally recommended if the person has developed symptoms very early on (for example in their 30s or 40s) or if there is a particular familial pattern.

If the doctor does not find a strong family history of dementia, they will not recommend that the person take a diagnostic genetic test.

What is the purpose of predictive testing?

Predictive genetic testing can be helpful for relatives of a person who has a single-gene change that causes dementia. A genetic test allows those relatives to know if they have the same gene change that will cause dementia in the future.

What are the benefits of predictive testing?

Having the test can be helpful for the following reasons:

  • It can remove the anxiety of not knowing – especially as the person approaches the age at which any symptoms of dementia are likely  to start.
  • It can give the person the option of entering into a clinical trial.
  • It can help with family planning.

Who can take a predictive genetic test?

To be assessed for a predictive test, a person or family will need to be referred to a clinical genetics service. This is a centre where specialist doctors and genetic counsellors work.

Does a negative result mean a person won't get dementia?

No. A person with a negative result on a predictive genetic test may still develop dementia. The predictive test only shows whether a person will develop the type of dementia that is related to that specific single-gene change. It does not rule out the possibility of that person developing dementia because of other factors.

Predictive testing and genetic counselling

Predictive testing can be stressful. If a person receives a positive test result, they will know for certain that they will develop dementia. This can be very difficult information to take in.

For this reason, predictive genetic testing will only be done with genetic counselling both before and after the test. This is to make sure that the person is aware of what it means to have the result of a genetic test, both for them and for their family. Many people have counselling but don’t then go on to take a test.

Predictive testing and getting insurance

Insurers are not allowed to ask anyone to take a predictive genetic test for dementia, or to declare the results of a test. A positive result (where the person has the changed gene) cannot be used to refuse someone life insurance or charge them a higher premium.

Dementia and family planning

If someone is known to carry a single-gene change that causes dementia, this may affect their plans to start a family. This is because there is a 1 in 2 chance of inheriting the same changed gene for any children they have.

In these cases, it is possible to try an approach called ‘pre-implantation genetic diagnosis’ (PGD).

What does PGD involve?

PGD involves the following steps:

  1. An egg is fertilised outside of the body – a process known as ‘in vitro fertilisation’ (IVF).
  2. The embryo is left to develop for a few days.
  3. Some cells are safely removed from the embryo.
  4. The DNA from these cells is tested for the specific gene change.
  5. Embryos without the gene change are implanted into the womb, where they should continue to develop.

What is the purpose of PGD for families affected by dementia?

Not every attempt at PGD works. However, when it is successful, PGD allows people affected by a familial dementia to have a child who is almost certain not to have the genetic change that the affected parent has. This means that the child will not develop the type of dementia caused by that gene change.

Does the parent need to know if they have a single-gene change that causes dementia?

Some people may think that they have a single-gene change and want to use PGD to make sure that their child does not have it. However, they may want to avoid finding out whether they themselves have the changed gene. It is possible in some centres to use the technology without the parent finding out if they themselves have the change.

Is PGD available on the NHS for families affected by dementia?

The NHS provides PGD services for families affected by familial Alzheimer’s disease or familial FTD. These families have to meet certain requirements to qualify for NHS funding and the NHS will only fund a set number of attempts.

PGD and genetic counselling

As with predictive genetic testing, families considering PGD are offered genetic counselling both before and after they go through the testing process.

Genetic testing for dementia risk variants

It is possible to have a genetic test for dementia risk variants, but this is not recommended outside a research setting.

Is it worth getting a genetic test for dementia risk variants?

Genetic tests for dementia risk variants are not recommended. This is because knowing whether someone has genetic risk variants does not mean knowing for certain whether they will develop dementia. A person who has risk variants may have a higher risk of developing dementia, but even someone at a higher risk may never develop the condition.

Should I get an at-home genetic testing kit for dementia?

The NHS does not provide testing for dementia risk variants. However, testing kits can still be bought over the internet. These tests are known as ‘direct-to-consumer’ (DTC) tests. These tests are not recommended by Alzheimer’s Society and most organisations who support people affected by dementia.

What does a DTC genetic test involve?

A DTC test involves sending a sample of saliva to the testing company by post. The company then analyses the saliva sample and sends the person their results.

Why are DTC tests not recommended?

There are many reasons why DTC tests are not recommended.

  • They are not as reliable as testing in an accredited genetics lab. This means that they may not be accurate.
  • They do not usually involve the input of a doctor, genetic counsellor or other health professional. This means that people may not understand what the test results mean for them and for their family’s future risk of dementia.
  • They are not recognised by GPs. The Royal College of GPs has advised GPs to ignore the results of DTC tests if people come to them with questions about inheritance. GPs will only refer people to genetics services if they find a strong family history of dementia. They will not consider a DTC test result when making a referral.
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