What causes young-onset dementia?

Younger people are much more likely to have an ‘atypical’ (unusual) form of Alzheimer’s disease. The symptoms depend on the specific form a person has:

• In posterior cortical atrophy (PCA) the first symptoms are usually problems with understanding visual information, such as struggling to read or judge distances.
• In logopenic aphasia the first symptoms are usually difficulties with language, such as problems finding the right word, or taking long pauses while they speak.
• In behavioural/dysexecutive Alzheimer’s disease the first symptoms are usually difficulties with planning and decision making, and behaving in socially inappropriate ways.

Up to 1 in 3 younger people with Alzheimer’s disease have one of these forms, but only 1 in 20 older people with Alzheimer’s disease have an atypical form. For more information see Rarer types of dementia.

Familial Alzheimer’s disease is a very rare form of Alzheimer’s disease. It is caused by genetic mutations (changes in genes) that run in families. Three genes have been found to have these rare mutations – PSEN1 (presenilin 1), PSEN2 (presenilin 2) and APP (amyloid precursor protein).

There is a 50% risk of a parent passing on the familial Alzheimer’s disease mutation to their children. People with the condition usually have a strong family history of the disease and will know a range of family members who were affected at a similar age, along with one of their parents.

Symptoms of familial Alzheimer’s disease usually start in someone’s 30s, 40s or 50s. The earlier the symptoms start, the more likely it is that the disease is genetic. Familial Alzheimer’s disease is very rare and probably accounts for fewer than 1 in 100 people with Alzheimer’s disease. For more information see Types of genetic testing.

Vascular dementia is caused by problems in the blood supply to the brain. It is closely linked to diabetes and to cardiovascular diseases such as stroke and heart disease.

Symptoms of vascular dementia vary from person to person. Early memory loss is less common. However, other symptoms are more common in vascular dementia, including slower speed of thought and problems with:

• planning
• organising
• making decisions
• solving problems
• following a series of steps
• concentrating.

Physical symptoms (such as limb weakness) are common in vascular dementia when a person develops it after a stroke.

For more, see What is vascular dementia?

Frontotemporal dementia is caused by damage to the lobes at the front and/or sides of the brain. It is much more common in younger people with dementia than in older people. FTD is most often diagnosed in people between the ages of 45 and 65. This is different to Alzheimer’s disease, vascular dementia and dementia with Lewy bodies, which all become more likely as people get older. There are three different types of FTD which cause different changes as the first symptoms.

For more information see Frontotemporal dementia: what is it?

Is FTD inherited?

About 20–40% of people with FTD have a family history of dementia. About 10% of people with FTD have a strong family history, with several close relatives from different generations affected.

The three main mutations causing FTD are in the progranulin (GRN), microtubule-associated protein tau (MAPT) and chromosome 9 open reading frame 72 (C9ORF72) genes.

The children or siblings of someone with a genetic mutation known to cause FTD have a 50% chance of carrying the same mutation. Families with a known mutation should be offered genetic counselling.

For more information see Genetics of dementia.

Dementia with Lewy bodies is caused by the build-up of tiny protein deposits (Lewy bodies) in the brain. DLB is less common in younger people with dementia than in older people. Lewy bodies also cause Parkinson’s disease and about one-third of people with Parkinson’s eventually develop dementia.

Symptoms of dementia with Lewy bodies can include hallucinations and varying levels of alertness. People can also develop the features of Parkinson’s disease (such as slower movement, stiffness and trembling limbs).

Alcohol-related brain damage is caused by regularly drinking too much alcohol over several years. It covers a range of conditions including alcohol-related dementia and Wernicke–Korsakoff syndrome. People diagnosed with ARBD tend to be in their 40s and 50s, and it is more common in men.

ARBD is caused by a lack of thiamine (vitamin B1), direct damage to nerve cells from alcohol, head injuries (caused for instance by falls or fights) and a poor diet.

At least 1 in 10 younger people with dementia may have ARBD. Symptoms will depend on the cause of the ARBD. They can include problems with planning, organising, problem solving, attention and controlling emotions. They can also include changes in personality, difficulties learning new skills and disorientation.

Many people diagnosed with ARBD who stop drinking alcohol and receive good support (including treatment and a good diet) can see improvement in their symptoms.  Sometimes they can make a partial, if not full, recovery.

For more information see Alcohol-related brain damage.

CADASIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy) is a rare genetic form of vascular dementia. It is a disease of the blood vessels in the brain. Symptoms include migraines and repeated strokes, loss of mental abilities, seizures, apathy and depression. They usually start when a person is in their mid 30s.

CADASIL is caused by a genetic mutation in the NOTCH3 gene. It is usually inherited from a parent who has a 50% chance of passing on the mutated copy of the gene.

For more information see Rarer types of dementia.