What is the science behind inheriting dementia?

In the second part of our blog series on dementia risk, Research Communications Officer Louise Walker explains more about the genetics of dementia.

‘Is dementia hereditary?’ is one of the most frequent questions that we receive here in the Research team at Alzheimer’s Society.

It is also one of the most searched-for terms on the Research part of our website.

However, as with many things in research, there is no simple answer!

There are many different forms of dementia and each form has its own underlying causes, including genetics.

For the majority of cases, genes do play a part but are not the whole story.

However, there are some rare forms of dementia which have a known genetic link.

In this blog I’ll explain a little more about what we know about the genetics of various forms of dementia.

Screenshot from a search engine

Alzheimer’s disease

Researchers and doctors often split Alzheimer’s disease into two categories. These are known as ‘later-onset’ and ‘early-onset’ or ‘younger-onset’.

The later-onset version of the condition is by far the more common and is usually diagnosed in people over the age of 65; those under 65 are usually diagnosed as having ‘younger-onset Alzheimer’s disease’.

As well as age, these two forms can sometimes be distinguished by differences in their genetics.

Younger-onset Alzheimer’s disease

Some cases of younger-onset Alzheimer’s disease have a known genetic component. These cases are sometimes called ‘Familial Alzheimer’s disease’.

Changes in genes called APP, PSEN1 and PSEN2 are known to cause the disease directly. This is because these genes are involved in the formation of the Alzheimer’s hallmark amyloid clumps, which are found in the brains of people with the disease.

The changes in the APP, PSEN1 and PSEN2 genes are very rare, and account for less than 1% (1 in 100) of all cases of Alzheimer’s disease.

If a doctor suspects a person may have an inherited form of the condition, either by family history or by developing the condition at a very early age (in your 30s, 40s or 50s), the person may be offered genetic testing. Their relatives may also be offered genetic testing.

In these cases, genetic counselling will be offered if the person is found to carry the disease-related changes

Later-onset Alzheimer’s disease

‘Later-onset’ Alzheimer’s disease is the most common form of dementia, affecting around 520,000 people in the UK.

Despite this form of Alzheimer’s disease also involving the amyloid protein, the APP, PSEN1 and PSEN2 genes have not been found to have a strong link to the development of this form of the condition.

There are some genes that are associated with increased risk of later-onset Alzheimer’s disease. The strongest known genetic risk factor is a gene called ApoE. You inherit one copy of ApoE from each parent and ApoE can exist in one of three forms – ApoE2, ApoE3 and ApoE4. If you have one or two copies of the ApoE4 version, this can increase your risk.

However, having ApoE4 does not mean you’ll definitely develop dementia. ApoE4 is the gene that most commercial ‘genetic testing’ kits are looking for when it comes to Alzheimer’s disease, but these tests cannot tell you whether you are going to develop dementia or not.

There are a number of other rare changes in certain genes that are each thought to contribute a little bit towards a person’s risk of the most common form of Alzheimer’s.

Researchers believe it may be a combination of several genes exerting a small effect, along with other factors such as lifestyle, which will influence a person’s risk of developing this form of Alzheimer’s disease.

What this all boils down to is that having a family member with Alzheimer's disease could mean that you are at an increased risk, but this alone isn’t enough to know whether you will go on to develop the disease.

Frontotemporal dementia

Frontotemporal dementia is a form that often affects people in their 40s and 50s.

Like younger-onset Alzheimer’s disease, some forms of frontotemporal dementia have a known genetic component.

The genes that are associated with frontotemporal dementia are called MAPT (which is associated with toxic tangles of the protein tau), progranulin (also called GRN) and C9orf72. 

The changes in these genes can be passed from parent to child and so genetic testing may be offered if a parent develops frontotemporal dementia. 

However, like younger-onset Alzheimer’s disease, not everyone with frontotemporal dementia has changes in these genes so having a parent with the condition doesn’t mean their children will definitely develop it.

What does this mean for me?

As you can see, the genetics of dementia are complicated.

Certain forms can be inherited from a parent, and those with younger-onset dementia are more likely to have genetic versions of the condition.

However, even in these cases the cause isn’t always clear-cut. If you have a family member with younger-onset dementia or a known genetic form of the condition, you should be offered genetic testing.

It is a very personal decision whether you undergo genetic testing and you should be offered counselling as part of the test.

You may also be interested in a project called ‘100,000 genomes’, which aims to understand more about these genetic forms of dementia.

When it comes to the more common form of Alzheimer’s disease and other forms of dementia such as dementia with Lewy bodies and vascular dementia, the genetic influences are less well-known.

At the moment, it is generally not possible to tell from a genetic test whether you will develop these conditions.

When it comes to dementia risk, we can’t control our genes but there are other elements we can control that could help to reduce risk. This includes not smoking, eating a healthy, balanced diet and managing conditions such as diabetes.

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I have found this 2 part blogs on Dementia very helpful and informative, as I continue to grapple with and care for my husband who has Vascular Dementia. Thank you.

makes no difference wifes dementia gets worse day by day my tollerance of her is shrinking,no help no hope.

Dear Paul, I can sympathise with you as I have had the same experience. Some help with practical things is available through the local authorities(usually!) but no help can be offered with things like trying to find missing items, coping with hallucinations and delusions, not being recognised, aggression, wandering etc. It is important to get your psychiatric team (via your GP) inviolved as soon as possible, and you will find masses of very informative factsheets available from The Alzheimers Society who have been wonderful. Medication, including antipsychotics such as Risperidone can make life for you much easier. Respite I find doesn't help much because you will constantly worry about what awaits you. If you can't cope,as I couldn't at the age of 80, then full time residential care is the best option.My wife has responded very well to the professionalism of her care home staff, is now calm, settled, free from anxiety etc but research your care home carefully as they can vary. It doesn't matter any more that on my weekly visit she is incoherent and unresponsive. The important thing is that she is not suffering, is kept clean despite double incontinence, eats well, participates in activities and feels secure in her new social environment. I wish you well.Your intolerance is natural but will be relieved. Just try to remember the good things in the past and don't let go completely, and don't give up hope!

My father is hallucinating a lot mainly people he is 80 and still driving comments please x

Hi Angela, thanks for your comment. Please do contact our Helpline team if you have concerns about your father. They can provide information, support and advice about dementia, and are available on 0300 222 11 22. Alternatively, you can read our information on hallucinations here: https://www.alzheimers.org.uk/info/20064/symptoms/110/perception_and_ha… Thanks again, and all the best.

My sister-in-law aged 73 has just been diagnosed with early onset Alzheimer's. Is that it? Or should she be having some form of treatment now, to perhaps help her memory. She has been offered nothing. Thank you.

Hi Denise, we're sorry to hear about your sister-in-law's recent diagnosis. Please do contact our Helpline team if you would like information, support or advice about dementia. They're available on 0300 222 11 22 and you can find out more about them here: https://www.alzheimers.org.uk/info/20012/helpline Alternatively, you can read our advice about treatments here: https://www.alzheimers.org.uk/info/20009/treatments Thanks again Denise, we wish you and your family all the best.

I have Ftd, i got Diagnosed at 42, i am 51 now and live in a nursing home in Australia , a cottage for young people with dementia, i lost a sister to these disease she was 56 when she died, my other sister had Ftd as well. i wish there was a tablet to slow the progress, but none as of yet, we need more services for Yod here

My big sis is in the later stage of Altzheimer's, my big bro seems to be in denial about his own condition, and for myself, while I try to stave it off, if I have it, then that's just part of living and dying... enjoy the ride, I'm sure I shall, no matter how strange... and I'll try not to be a pain to others, but who knows? I most probably won't know, but I like to think I'll be conscious enough to recognise my last gasp.

My mum is 80 and in hospital. She recognises me but forgets my dad who she has been married to for 61 years she tells me very mixed up stories about nothing She goes to toilet then comes out and is suprised thinking I've moved her to a better room (hospital) she has trouble working out how to turn the tap on ,,,,,breaks my heart

I have been told by my GP I have ‘mild cognitive impairment’ at the moment but GP said can’t offer any advice etc to help me or possibly slow it down! I find this very frustrating so I trawl through text books for advice on how I might slow it down. I know my mother who is dead now ‘developed’ Alzheimer’s and to watch her deteriate and die in her own world was awful.

Hello Chris,

Thank you for getting in touch. We’re sorry to hear you’re going through such a frustrating time.

If your mother developed Alzheimer’s disease at a late age, then the chances of passing on the disease genetically are fairly low. However, if your mother developed it at a younger age (<65 years), then the chances are somewhat higher.

We would suggest discussing the possibility of genetic testing/counselling with the clinician who diagnosed your mild cognitive impairment (MCI). Learn more about types of genetic testing: https://www.alzheimers.org.uk/about-dementia/risk-factors-and-prevention/types-genetic-testing

Many people develop MCI and do NOT go on to develop dementia, especially if they develop it at a later age (>70 years or so). So, if you are worried about the loss of independence associated with dementia, you might take some comfort in knowing that, while dementia is a possibility, it is by no means inevitable just because you have a mild loss of cognitive function now.

Our factsheet on MCI explains this in more detail: https://www.alzheimers.org.uk/sites/default/files/pdf/factsheet_what_is…

Please call the National Dementia Helpline on 0300 222 1122 for further information, advice or support. Our advisers are available Monday to Friday (9am-5pm), extending to 8pm on Monday, Tuesday and Wednesday; Saturday to Sunday (10am-4pm).

We hope this helps, Chris.

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