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, or had 3 brothers the eldest died a week ago, aged 94. The younger of the three died 1 yr ago. 8th Oct. Aged 84 the middle one has been in a home for several years. Age 91. All had a form of dementia/Alzheimer’s . I have not had much contact with them, one lives in America, one in Canada and one south coast of England. I live in Scotland. My mother, father and sister died of cancer. Is there anything that I should do to check if I may have dementia, or find some way of protecting myself, I am 79? Thank you. Sylvia

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Hi Sylvia,

Thanks for your comment. I'm very sorry to hear about your brothers.

I wasn't quite sure from reading your message if you have been experiencing symptoms of dementia yourself, or are just worried about the possibility? If you are experiencing dementia symptoms, the best thing you can do is talk to your GP. You can read more about symptoms of dementia here: https://www.alzheimers.org.uk/about-dementia/types-dementia/symptoms-de…

We also have a free booklet for people who are worried about their memory, which you may find useful: https://www.alzheimers.org.uk/get-support/publications-and-factsheets/w…

It's important to say that the majority of dementia is not inherited. There are some exceptions, and you can read more about types of dementia that can and can't be inherited here: https://www.alzheimers.org.uk/about-dementia/risk-factors-and-preventio…

In terms of reducing your risk of dementia, there are some things you can do to help: https://www.alzheimers.org.uk/about-dementia/risk-factors-and-preventio…

I hope these resources are helpful, Sylvia. You can also call our Dementia Connect support line on 0333 150 3456 and speak to a trained dementia adviser. They will be able to learn more about your situation and give information, advice and support.

Best wishes,

Alzheimer's Society blog team

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My mother developed early onset dementia when she was 53. We lost her ten years later after a crippling decline which completely devastated our family.

She was an incredible, highly intelligent, much loved lady. She was also an alcoholic. No one ever explained to me whether this was connected with her condition... so I am left with uncertainty and confusion as I go through life, now raising a family of my own.

I’ve never really considered her decline in the context of ‘is it hereditary?’ as I have been too consumed by the loss of my mother to think of it in those terms. I’m 42 now and it does creep into my mind.

Should I take the genetic test? Would I be able to access her medical records to uncover information which I might have been protected from by well-meaning family members?

Thank you.

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Hi Lucy,

Thanks for getting in touch - and sorry to hear about your mother.

We have a blog on genetic testing which you may find helpful: https://www.alzheimers.org.uk/blog/what-can-genetic-tests-tell-us-about…

Dementia is incredibly complex and there is rarely one single cause. Very few people will inherit dementia from a parent, and there are many other factors including age, lifestyle and overall health that can have an impact.

It's completely understandable that this could still be causing you uncertainty and confusion. So if this is worrying you, please call our Dementia Connect support line on 0333 150 3456 for more information, advice and support. More details on our phone support (including opening hours) are available here: https://www.alzheimers.org.uk/get-support/national-dementia-helpline

Hope this is helpful,

Alzheimer's Society blog team

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My mum developed Alzheimer’s at 57 & passed away at 70 . We had a truly awful, incredibly stressful 6yrs before she went into hospital. She spent her last 7yrs in a hospital bed, doubly incontinent, no speech, being hoisted onto a shower trolley & spoon fed liquidised meals. She wasn’t even aware of our presence. My mum was an attractive, stylish woman with a fantastic personality & my dad adored her ( he died very suddenly of a broken heart 13 months before her). She was slim, didn’t smoke, drink, had a healthy diet & an active lifestyle. She was the last person anyone would have imagined to have been struck down with this hideous disease that robs you of everything. There is no family history on either side that I am aware of. My mum appears to have been the first. However this doesn’t stop me from worrying myself sick that the same awful fate awaits me & the closer I get to the age my mother was (57) I am 51, the more it’s on my mind. Do I have good reason to be worried ?

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Hi Tracy,
Thanks for getting in touch. It sounds like your family went through a really stressful time.
If you're feeling worried, we recommend speaking with one of our dementia advisers on 0333 150 3456. They can listen to your situation, provide advice and support. Our advisers are available seven days a week. You can find opening hours for our Dementia Connect support line here: https://www.alzheimers.org.uk/get-support/dementia-connect-support-line
We hope this helps, Tracy.
-
Alzheimer's Society blog team

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My father is in the process of being tested for dementia, I am quite worried that there may be something genetic going on as he is only 60. Other than this as a teenager I remember my grandmother having the same symptoms as my dad and unfortunately just before she got round to having the CT head she passed away from sepsis so we never found out what she had, but she was 75 though. After this I then found out that my great grandmother had to go into a mental institution in her 50s, a great aunt of me told me that it was because she lost her mind and memory, but that was it.

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Hello Ann, thanks for getting in touch.
We're sorry to hear about the difficult times you and your family are going through.
You might find our page 'Is dementia hereditary?' a helpful way to answer some questions you may have regarding dementia being passed through the family. https://www.alzheimers.org.uk/about-dementia/risk-factors-and-preventio… This should help you understand the genetic links for different types of dementia.
In the meantime, if you would like to speak with one of our dementia advisers on the phone, they're available seven days a week to give you the support you need. Please call 0333 150 3456. You can find opening hours here: https://www.alzheimers.org.uk/dementiaconnect
Wishing you all the best, Ann.
-
Alzheimer's Society blog team

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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.
Chris.

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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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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

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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.

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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

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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.

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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.

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

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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.

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

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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!

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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.

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