Genes & dementia - Alzheimer's Research UK (2024)

As dementia is so common, many of us will have a relative living with the condition – but this does not mean we will develop it too.

Dementia is caused by diseases that affect the brain, such as Alzheimer’s disease. The likelihood of developing one of these diseases will usually depend on a complex mix of factors like our age, medical history, and lifestyle, as well as our genes. Most cases of dementia are not directly caused by genes we inherit from our parents.

Genes determine our traits, such as our eye colour and height. In some cases, they can determine whether we will develop a disease or not. They are “passed on” or inherited from our parents.

Every cell in our body contains thousands of genes. Each gene is a portion of DNA ‘code’, which holds the information our cells need to make a specific protein. These proteins are the building blocks of life. They make up our tissues and organs, and many have specific functions, like carrying messages between our nerve cells.

The DNA code in our genes naturally varies from person to person. Often this variation has no effect on us, but sometimes the DNA code can contain differences that slightly alter the protein made by a particular gene, causing it to work differently. This can lead to changes in processes in our cells, which may increase (or sometimes decrease) our likelihood of developing a disease. These are known as risk genes.

If we inherit risk genes from their parents, this does not mean we will definitely get dementia. Most people’s risk of developing dementia is a combination of genes, lifestyle, environment, and age. We cannot change our age or genes, but some research has found that even if we carry a risk gene, there are still things we can do to reduce our risk.

In very rare cases, a person may inherit a gene that does not work properly from one of their parents. This faulty gene, sometimes called a mutated gene, can cause a person to develop a disease no matter what other risk factors they have.

Rare types of Alzheimer’s disease, and some cases of frontotemporal dementia, can be caused by faulty genes and are passed down from an affected parent. Someone who carries one of these rare mutations is extremely likely to develop the disease during their lifetime. Around one in 100 cases of dementia are caused by inherited faulty genes.

Late onset Alzheimer’s disease affects people over the age of 65. It is the most common type of Alzheimer’s, and research suggests that it’s caused by a combination of risk factors including age, genes, lifestyle and environment.

To date, scientists have found versions of over 75 different genes that are associated with an altered risk of developing Alzheimer’s disease. However, having one of these versions may only have a small effect on our overall risk. There is still a lot to be understood about these genes and their role in the development of late onset Alzheimer’s.

The best understood risk gene, with the largest effect on Alzheimer’s risk, is called APOE. This gene makes a protein that helps keep our brain cells healthy. There are three different versions of it – APOE2, APOE3 and APOE4 – and everyone carries two copies of it - one from each parent.

People who inherit one copy of APOE4 (roughly one in four people) are around three times more likely to develop late onset Alzheimer’s disease. About one in 50 people inherit two copies of APOE4 – one from each parent. They may be more than eight times more likely to develop Alzheimer’s. However, due to other contributing factors, such as age and lifestyle, people who inherit APOE4 – from one or both parents - still may never develop the disease.

Late onset Alzheimer’s is not directly inherited through faulty genes.

More information about Alzheimer's disease

Genetic tests can be used to tell whether someone has inherited a gene linked to a particular disease, and to estimate their chances of developing that disease later in life.

Genetic testing for Alzheimer’s disease risk genes is not available on the NHS. This is because most of the genes discovered so far only have a relatively small effect on someone’s overall risk of developing late onset Alzheimer’s disease, and many people who inherit these genes will not develop it. Equally, people who do not have risk genes may still develop the disease.

Around one in 20 people with Alzheimer’s disease are diagnosed with the condition at a younger age, usually in their 50s or early 60s. For many cases of young onset Alzheimer’s, the cause is still unclear but is likely due to a complex interaction of genes and lifestyle.

A very small number of young onset Alzheimer cases are caused by a faulty gene passed down in families. This is called ‘familial Alzheimer’s disease’ (FAD) or ‘young onset inherited’ Alzheimer’s. It usually affects many members of the same family at every generation, typically in their 30s, 40s or 50s. The faulty gene is passed down directly from a parent who has the disease to their child, it does not skip generations.

So far, three genes have been linked to young onset inherited Alzheimer’s disease. These genes are called:

• amyloid precursor protein (APP)
• presenilin 1 (PSEN1)
• presenilin 2 (PSEN2).

These genes are involved when cells produce a protein called amyloid. If the gene is faulty, it causes an abnormal build-up of amyloid in the brain, which forms clumps or ‘plaques’ which damage brain cells and are part of how Alzheimer’s disease develops.

People who carry one of these faulty genes will develop Alzheimer’s, and their children have a on in two (50%) chance of inheriting the gene and developing the disease too. It is important to stress that faulty versions of these genes are very rare and only account for one in 100 (1%) cases of the disease.

Find out more information about young onset Alzheimer’s disease.

If someone has an obvious family history and pattern of Alzheimer’s affecting every generation at a young age, genetic testing may be available on the NHS. A blood test is used to confirm a mutation in the PSEN1, PSEN2 or APP genes. This is known as diagnostic genetic testing.

The Familial Alzheimer’s Disease (FAD) Support Group helps families affected by mutations in the PSEN1, PSEN2 or APP genes. More information can be found at the Rare Dementia Support website. You can also emailcontact@raredementiasupport.orgfor support.

More information about genetic testing can be found further down this page.

Frontotemporal dementia (FTD), sometimes called Pick’s disease, is a rarer type of dementia mostly affecting people under the age of 65 years. The symptoms of FTD can be quite varied but include changes to behaviour, communication and language. There are different types of FTD that have different underlying causes.

Some people with FTD have a family history, and the condition may be inherited in some of these families. In a particular form called ‘behavioural variant’ FTD, a third to half of people affected may have a family history. This figure is thought to be much lower for other types of FTD.

Overall, around one in 10 cases of FTD are thought to be caused by a faulty gene passed down in families. Several genes have been found that causes these inherited types of FTD, including:

• MAPT (tau)
• GRN (progranulin)
• C9ORF72

Mutations in the MAPT gene can cause the protein it makes, called tau, to behave abnormally, forming toxic clumps that can damage brain cells. Researchers are less certain about how mutations in GRN (progranulin) and C9ORF72 cause the disease.

The C9ORF72 gene can cause people to develop motor neurone disease, FTD or both conditions and may affect members of the same family differently.

In cases of FTD that are not caused by faulty genes, the risk factors are not yet fully understood, and research is ongoing.

More information about frontotemporal dementia

If there is a strong family history of frontotemporal dementia, genetic testing is available on the NHS to look for the faulty genes known to cause the condition. You can talk to your doctor if you are concerned about a strong family history of frontotemporal dementia.

The Frontotemporal Dementia (FTD) Support Group helps families affected by frontotemporal dementia. More information can be found on the Rare Dementia Support website. You can also emailcontact@raredementiasupport.orgfor support.

More information about genetic testing can be found further down this page.

Vascular dementia is caused when blood flow to the brain is reduced, damaging nerve cells. This can happen as a result of a stroke or damage to blood vessels deep in the brain. The majority of cases of vascular dementia are not caused by faulty genes.

However, there are risk genes that affect a person’s chances of having a stroke, heart disease, high blood pressure or high cholesterol – which can all contribute to vascular dementia. But age and lifestyle factors - such as smoking, lack of exercise, drinking alcohol over the recommended limits, and an unhealthy diet – can also increase someone’s risk.

There are rare genetic disorders that can cause vascular dementia by damaging blood vessels in the brain. One is called CADASIL (which stands for ‘cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy’) which can be passed down through families. CADASIL only affects around 1,000 people in the UK.

More information about vascular dementia

Dementia with Lewy bodies (DLB) is caused by a build-up of abnormal proteins called Lewy bodies in the brain. It can have symptoms similar to those seen in people with Parkinson’s disease.

Age is currently the biggest known risk factor for DLB, although research is underway to find out whether genes may also play a role.

More information about dementia with Lewy bodies

People with Down syndrome are born with an extra piece of DNA in all their cells. This means they have an extra copy of the APP (amyloid precursor protein) gene. This leads to the build-up of amyloid plaques in the brain, which play a role in the development of Alzheimer’s disease. While not everyone with Down syndrome will go on to develop symptoms of Alzheimer’s, most people with the condition over the age of 40 will have amyloid build-up in their brains. It is estimated that about half of people with Down syndrome develop symptoms like memory loss, usually in their 50s and 60s.

To find out more about Down syndrome and dementia you can contact Down’s Syndrome Association's helpline on 0333 1212 300 or visit their website.

Having a test to look for a faulty gene that causes dementia is only appropriate for a very small number of people. This is because inherited dementia is rare.

If you are worried that you have a strong family history of young onset Alzheimer’s disease or frontotemporal dementia, you can speak to your GP about this. For various reasons, not everyone will know whether they have a strong family history of dementia. In these circ*mstances, you can speak to your GP.

Deciding to take a genetic test to see if you have an inherited type of dementia is a big decision and needs very careful thought. Some people may not wish to know if they carry a faulty gene that causes dementia. Others may feel it would help them and their families to plan for the future.

It is also worth bearing in mind that not all mutations that cause dementia have been identified. This means that some families may have many affected members, but no mutation can be found. Therefore, a negative test result cannot always rule out a genetic cause of a disease.

If a test is appropriate, your doctor should be able to refer you to a genetic counsellor or specialist. This could be a cognitive neurologist or memory clinic psychiatrist. They will discuss with you the pros and cons of taking a test and what will be involved. They will also tell you where the results will be kept, who they will be shared with, and what the next steps would be. For people found to have a genetic mutation that causes dementia, these discussions will also cover the options available if you are considering starting a family.

Within one family, any blood relative who may be at risk of inherited dementia can be offered genetic counselling. Several months of genetic counselling are required before someone can undergo genetic testing. This allows time to discuss what a potential test result may mean, considering things like finances, insurance, and family planning. Genetic testing is not the right decision for everyone, and you can still choose to decline testing after a period of genetic counselling.

To find out more about genetic testing and what support is available you can visit the Rare Dementia Support website or call 0203 325 0828.

You can read a personal account about deciding to be tested for a gene mutation on our blog.

Our video series “Genetic testing for dementia” includes a film containing first-hand accounts of being tested for genetic forms of dementia, and a series of frequently asked questions, answered by Prof Nick Fox, Director of the Dementia Research Centre at UCL. You can find the playlist below.