Rare causes of dementia
Dementia information
There are several rare conditions that can lead to dementia or dementia-like symptoms. Around 35,000 people in the UK are thought to be affected by these rarer causes of dementia.
For every 100 cases of dementia, five are due to a rare condition.
In comparison, for every 100 cases of dementia, 65 are due to Alzheimer’s disease. Alzheimer’s is the most common cause of dementia.
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What is dementia?
Dementia is not a disease in itself. It is a word used to describe a group of symptoms that occur when brain cells stop working properly.
This happens inside specific areas of the brain and can affect how you think, remember, move and communicate.
The symptoms of dementia are caused by diseases that affect the brain.
There are several of these diseases, and the most common are:
There are also rarer diseases and conditions that can lead to dementia.
What is a rare disease?
A rare disease is defined by the UK Government as one that affects fewer than one in every 2,000 people.
If you’re worried you or a loved one may be experiencing symptoms of any of the conditions listed on this page, speak to a doctor. They can run some tests to help find out what is causing them.
Getting an accurate diagnosis allows someone to access the right treatments and support for them. It also provides the chance for people to plan ahead.
CADASIL
CADASIL is a rare, inherited condition that can cause vascular dementia. It only affects around 2,000 people in the United Kingdom.
CADASIL is caused by faulty genes that cause blood vessel walls to thicken. This means less blood can flow around some areas of the brain. This makes people with the CADASIL mutation more likely to develop vascular dementia.
CADASIL is passed from a parent to their child. A person who has a parent with the mutated gene has a one in two chance of inheriting the gene themselves.
Chronic traumatic encephalopathy (CTE)
Chronic traumatic encephalopathy (CTE) is a brain condition associated with repeated blows to the head.
Someone who played a lot of contact sports at a professional level may be at higher risk of CTE in later life. Examples of these sports include rugby, American football or boxing.
Early symptoms of CTE usually appear around 10 years after brain injuries. Changes can be gradual and not always noticeable at first.
People with who experience traumatic brain injuries are more likely to develop dementia. However, head injuries can vary, and so can the diseases that cause dementia. This makes the relationship hard to unravel.
CTE is linked to the build-up of a protein called tau.
What is tau?
Tau naturally occurs in the brain and only becomes harmful when it starts to clump together.
In healthy brains, tau supports the internal structure of our cells and helps to transport essential nutrients and molecules.
In some of the diseases that cause dementia, tau breaks away from the “scaffolding” and becomes free inside the cell.
When this happens, tau proteins start to stick together and form clumps, or tangles. These tangles disrupt the cell’s transport system and damage its structure, eventually leading to cell death.
Over time, this damage spreads through brain networks, contributing to the symptoms of dementia.
Corticobasal syndrome (CBS)
Corticobasal syndrome usually affects people aged between 50 and 70. The condition is estimated to affect five people in every 100,000.
You may also hear it called corticobasal degeneration (CBD).
CBS is caused by damage to cells on the surface of the brain, called the cortex, and a deep part of the brain called the basal ganglia.
We don’t know what damages the cells and causes them to die. However, researchers have found many harmful proteins in the brains of people with CBS. Research is trying to find out why these build up, and how they affect the brain.
CBS is linked to the build-up of a protein called tau.
Everybody has tau in their brains, but it is usually broken down before it reaches high levels. In some people, it can become sticky and clump together.
As these clumps spread throughout the brain, more brain cells become damaged. Over time, this leads to the brain shrinking (atrophy). This can cause the symptoms a person experiences.
Progressive supranuclear palsy (PSP)
PSP is thought to affect over 5,000 people in the UK. This is roughly eight in every 100,000 people.
Progressive: gets worse over time
Supranuclear: damage to the brain that affects eye movements
Palsy: muscle weakness
PSP is caused by damage to areas of the brain that control thinking and body movement, including the brainstem, cerebellum and basal ganglia.
PSP is linked to an abnormal build-up of tau protein, similar to Alzheimer’s disease and frontotemporal dementia. Tau build-up is also linked to other rare causes of dementia.
Creutzfeldt-Jakob disease (CJD)
CJD is a very rare disease, caused by a type of abnormal protein.
When the body makes proteins, it folds them into a shape that is functional. When proteins misfold at this stage, they become harmful.
These misfolded proteins may become prions. Prion proteins clump together and cause brain cells to die, resulting in sponge-like brain tissue.
There are different types of CJD:
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Sporadic CJD
Sporadic CJD develops for no known reason. It is the most common type of CJD.
In the UK, sporadic CJD usually starts in a person’s 60s. It affects one in every 500,000 people in the UK per year.
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Familial CJD
Familial CJD is an inherited form of CJD. Someone develops CJD because they have inherited faulty genes from one of their parents.
The disease starts between 30 and 55 years old. It affects one in every nine million people in the UK.
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Acquired CJD (variant CJD)
Acquired CJD (variant CJD) is when someone comes into contact with abnormal prion protein. For example, by eating meat from a cow that had bovine spongiform encephalopathy (BSE or ‘mad cow disease’).
The average age of symptoms of acquired CJD is 26 years.
There have been only 178 confirmed cases in the UK between 1970 and 2016. These cases are extremely rare since infected animals were from the food chain.
There have been no recorded deaths from acquired CJD since 2016.
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Iatrogenic CJD
Iatrogenic means illness caused by medical or surgical treatment.
Contaminated blood transfusions or donated tissues from people who died with CJD can cause iatrogenic CJD.
There has been one death from iatrogenic CJD since 2020.
Huntington's disease
Huntington’s disease is an inherited condition affecting the brain and spinal cord. It is caused by a faulty gene, which they have inherited from their parents.
Genes are the instructions that tell our bodies what to do. When genes have a mistake in their instructions, it can cause diseases like Huntington’s.
Huntington’s disease may appear at any age but usually develops between the ages of 30 and 55.
It is thought that there is around 8,000 people living with Huntington’s disease in the UK. That is 13 people out of every 100,000.
Alcohol-related cognitive impairment
Long-term, moderate to heavy alcohol consumption can have a negative effect on brain function, memory, and our ability to process information.
Research has found that excessive alcohol consumption may cause the brain to shrink and become damaged.
Alcohol-related cognitive impairment may also be called alcohol-related brain damage.
If treated in the early stages, the memory and thinking problems caused by significant alcohol use can get better.
The NHS defines significant alcohol use as:
- for men: an average of 35 drinks (50 units) per week
- for women: an average of 28 drinks (35 units) per week.
It is important to speak to your doctor if you think you might be drinking too much alcohol.
People who drink heavily long-term are at risk of irreversible alcohol-related brain damage.
Korsakoff syndrome
Korsakoff syndrome is a form of dementia most commonly brought on by long-term alcohol misuse.
It often follows an episode of Wernicke’s encephalopathy, a medical emergency caused by a sudden lack of thiamine (vitamin B1). Long-term heavy drinking makes it harder for the body to absorb thiamine.
Thiamine helps regulate energy and keeps the nervous system healthy, so when the body doesn’t absorb it properly, dementia-like symptoms can develop.
Treating Wernicke’s encephalopathy quickly can prevent Korsakoff syndrome.
HIV-associated dementia
HIV (human immunodeficiency virus) is an infection that weakens the body’s immune system.
In 2024, around 104,000 people in the UK were thought to be living with HIV. That is less than two cases of HIV per 1,000 people
HIV-associated dementia (HAD) is a condition that falls within the spectrum of HIV-associated neurocognitive disorders (HAND).
As people living with human immunodeficiency virus (HIV) get older, they may be more likely to experience symptoms of HAD.
People living with HIV can become very unwell from something like a common cold, because their immune system is not as strong.
A complication of having an infection when living with HIV can also lead to memory and thinking problems.
Frontotemporal dementia with motor neurone disease
Frontotemporal dementia with motor neurone disease (FTD-MND) is a rare overlap of two conditions.
Frontotemporal dementia (FTD) is where cells begin to die in areas of the brain called the frontal and temporal lobes.
Motor neurone disease (MND) is a condition which affects the brain and spinal cord.
FTD alone is a rarer cause of dementia. It is responsible for 12 out of every 100,000 cases of dementia. Around one person out of these 12 cases will develop FTD-MND.
MND is also a rare condition. In 2025, experts estimated that 13 out of every 100,000 people have a form of MND. Research suggests that around three of these people will also be diagnosed with FTD as the disease progresses.
This information was updated in February 2025 and is due to be reviewed in February 2028. It was written by Alzheimer’s Research UK’s Information Services team with input from lay and expert reviewers. Please get in touch if you’d like a version with references or in a different format.
This information is produced with support from The Perfume Shop who had no input into the content.
