In around 30-40% of people diagnosed with frontotemporal dementia (FTD), there is a family history of the condition and it is likely to have a genetic cause – we call this familial FTD (fFTD).

FTD is subdivided into two types:

1. Behavioural variant FTD (bvFTD), which mainly affects behaviour and personality
2. Primary progressive aphasia (PPA), which mainly causes a loss of speech and language abilities. These include progressive nonfluent aphasia (PNFA) and semantic dementia (SD).

Of the different forms of FTD, the behavioural variant or bvFTD is the one that is inherited most often. Primary progressive aphasia (PPA), and particularly the PNFA form, can also have a genetic cause and run in families but it is much rarer.

For more detailed information on the different forms of FTD please visit our Understanding FTD and Understanding PPA pages.

Causes

In some cases FTD appears to run in families and there is likely to be a genetic cause.

In 30-40% of all people with FTD, the condition is known to be caused by an abnormality in a single gene. Three genes cause the majority of genetic FTD cases – progranulin, tau and C9orf72. At least six other genes can cause familial FTD, and more may be discovered.

In most people (50-70%), frontotemporal dementia (FTD) is a sporadic condition. This means that FTD occurs in an individual person by chance, without anyone else in the family having been affected. In most cases, the relatives of someone who has been diagnosed with FTD do not have an increased chance of also getting this condition.

You can find out more about genes and typical Alzheimer’s disease by visiting the Alzheimer’s Research UK website.

How likely am I to inherit fFTD?

If someone has one of the gene abnormalities that cause FTD, then each of their children has a 50% chance of inheriting the faulty gene. Each sibling of someone with the faulty gene also has a 50% chance of inheriting it.

The age at which symptoms of FTD begin is very variable. Some people develop FTD around the same age that their parent developed it. However, for other people, there can be up to 20 years’ difference in the age that FTD develops.

If someone is tested and has inherited one of these gene abnormalities, then they are highly likely to develop FTD. Only a very small minority of people who have inherited a faulty gene live without developing FTD in their lifetime.

Genetic testing and counselling

In families where a gene abnormality is known or suspected, expert genetic advice is important.

If someone is worried about their risk of developing familial FTD or wishes to discuss it further, their GP will be able to refer them to a specialist genetic counselling service to discuss their concerns and arrange genetic testing if needed.

The results of any genetic test have important implications not only for the person being tested but also for the rest of the family. It is important to discuss these carefully with a specialist who has expertise in genetic counselling and is familiar with the family, before any genetic tests are performed.

A genetic test for FTD can be performed on a blood sample and is usually done because several other family members have FTD or an associated disorder. However, it may also be performed when symptoms or brain scans suggest familial FTD. For more detailed information on genetic testing and counselling for FTD, please our I think I am at risk of fFTD. What next? page.

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