Genes are just one of many factors that determine our risk of dementia. The number of people who inherit dementia from their parents is very small. So what can and can’t genetic tests tell us?
Genetic testing hit the headlines recently, after the Mirror Online's report of a 23-year-old man told that he had inherited dementia from his mother.
Alzheimer’s Society received lots of concerned comments and questions in response to the article. So here we will outline the basics of the genetic tests available for dementia and most importantly what they can and can’t tell us.
With 850,000 people across the UK living with dementia today, 1 in 4 people over 55 have a close relative with the condition. Inevitably relatives often worry about the possibility of inheriting the dementia.
It’s important to remember that the number of people who inherit dementia from their mother or father is very small. The majority of cases of dementia are down to chance, other medical factors, lifestyle factors and risk genes.
Testing for risk gene variants
Genes can come in many different forms, and particular forms of specific genes can affect our risk of developing dementia. These are called risk gene variants. The effects of these gene variants are very subtle and can slightly increase or slightly decrease our risk of developing dementia. They do not directly cause dementia.
These risk gene variants are influenced by age, lifestyle, other genes and overall health to determine whether we might go on to develop dementia. They are by no means the only factor at play.
Of all the causes of dementia, we know the most about the genetics of Alzheimer’s disease. But testing for these genetic variants cannot tell us whether someone will go on to develop Alzheimer’s or not. For this reason, there is no test for these risk genes available through the NHS. Even if you test positively for one or even two copies of a variant you cannot be sure if you will develop the disease.
Tests for some gene variants are available over the internet and generally do not involve a doctor or counsellor. This type of testing is controversial and is not recommended by most specialists, firstly because it doesn’t tell us anything for certain. Secondly, genetic counselling is not always offered which is important to make sure that getting this information is the right decision for you. There are concerns that private companies do not always offer enough support to those receiving results so they fully understand what they mean.
Testing for single gene variants
There are specific variants in our genes which can be inherited from our parents that do cause dementia. However it’s important to remember that these are very rare. Familial Alzheimer’s for example, is directly inherited through single gene variants but is thought to affect only 600 families around the world.
In some other forms of dementia such as frontotemporal dementia (FTD) it is slightly more common. Up to 30 per cent of people with FTD are thought to have the condition due to a gene they have inherited from their mother or father.
Inherited forms of dementia are rare so shouldn’t be a concern for most people
It’s natural for relatives of someone with dementia to be worried about whether they might also go on to develop the condition. Inherited forms of dementia are rare so shouldn’t be a concern for most people. People who don’t have any symptoms can be tested, but generally only if a close relative is known to have one of the rare genes that directly causes dementia. This is known as predictive genetic testing because if someone does have the rare gene, they will almost certainly develop dementia.
There are specific gene mutations that cause Huntington's disease, familial Alzheimer's disease and in some cases frontotemporal dementia.
Before considering single mutation genetic testing
As we have mentioned genetic testing for risk gene variants isn’t thought to be very informative and so isn’t encouraged by specialists.
Testing for rare single gene variants is an option in some circumstances and is generally only offered if there is a strong pattern of dementia in the family. Genetic testing should be accompanied by genetic counselling. The decision is a very personal one and there is no right or wrong choice. Counsellors are able to help you talk through whether you want to find out, and if so, whether it’s the right time.
As we have mentioned in this blog, in some cases our genes affect our chances of whether we will go on to develop dementia. However dementia is incredibly complex and there is very rarely one single cause. There are many other factors including age, lifestyle and overall health that also have an impact.
Unfortunately dementia is a common condition and over 1 million people will be affected in the UK by 2021. Alzheimer’s Society is here to support everyone living with the condition, today and in the future, to live well and to unite against dementia.
Learn more about genetic testing
Learn about testing for single-gene mutations, diagnostic genetic testing, predictive gene testing and counselling that is available.