It is well known that children can take after their parents – for example, in the way they look. This is partly because many of the key characteristics of a person are passed down from parents to children in their genes.

What are genes?

Genes are made from a chemical called DNA. They contain information that is needed to make proteins, which the body is built from. Humans have over 20,000 different genes. Most often, a person has two copies of each gene – one inherited from each parent.

What is a gene variant?

The same gene can differ between individuals – these are known as ‘gene variants’. These can help to explain why people are different to each other – for instance, why one person has blue eyes and another person has brown eyes.

If a gene variant increases a person's risk of developing a disease, it is known as a 'risk variant' for that disease.

How can genes cause dementia?

Most often, dementia is caused by a complex disease in which genes are only one factor. When this happens, the dementia develops as a result of many different factors. In these cases, genes do not directly cause it to develop.

It is not possible to directly inherit dementia when it is caused by a complex disease.

Dementia caused by a complex disease

Nearly all cases of dementia are the result of a complex disease. In these cases, genes may increase the risk of developing dementia, but they don’t cause it directly.

When dementia is the result of a complex disease, it is likely to be caused by a combination of risk factors. These include:

• non-genetic factors – for example, members of the same family may all smoke or have an unhealthy diet, which are both risk factors for dementia.
• genetic factors – a person may inherit the same dementia risk variants as other members of their family. This could include variants in genes such as APOE.

These factors are often shared by members of the same family. This is why many people have some family history of dementia – for example, they may have a parent who developed dementia in their 90s and a brother who developed dementia in his 70s. This is not the same as ‘familial dementia’.

Can a person with dementia risk variants reduce their chances of developing dementia?

Yes. People with risk variants for dementia can still reduce their chances of developing the condition by leading a healthy lifestyle. For example, if the person eats a well-balanced diet, is physically active, doesn’t smoke and doesn’t drink too much alcohol, they will reduce their overall risk of developing dementia.