In the majority of cases, the cause of young onset dementia is a combination of our genetics, lifestyle, and environmental factors. Research is ongoing to understand why some people are affected at a younger age than others.
Some types of young onset dementia have more of a genetic susceptibility, this means we can inherit genes from our parents that increases our risk of developing one of these diseases at a younger age.
Most cases of Alzheimer’s are not directly inherited. However, cases below the age of 65 are slightly more likely to be inherited compared to late onset Alzheimer’s. Directly inherited Alzheimer’s is where a parent with the disease passes a gene on to their children, who also then develops the disease. It is thought that around 11% of cases of young onset Alzheimer’s may be directly inherited, this is sometimes referred to as familial Alzheimer’s.
Three genes - APP, PSEN 1 and PSEN 2 - have been found that play a role in the development of familial Alzheimer’s. Mistakes in these genes (called mutations) can cause the build-up of a toxic protein called amyloid in the brain, which is a key feature of the disease.
In FTD, there is a build-up of proteins in the frontal and temporal lobes of the brain. Three proteins are involved in FTD, called tau, TDP-43 and FUS. These proteins clump together and damage the brain cells, eventually causing them to die.
In young onset FTD, about one in 10 cases are caused by a directly inherited gene. This is passed down from a parent who is affected to their child, and the chances of passing the gene on to a child is 50/50 (one in two chance). This type of FTD is called familial FTD and there is a strong pattern of inheritance in every generation.
If you’re worried about directly inherited dementia, speak to your doctor who can refer you for specialist testing called genetic counselling. You can find out more about genes and dementia on our webpages here or contact us on 0300 111 5111 or firstname.lastname@example.org and ask for our booklet “Genes and dementia”
Young onset dementia
This leaflet aims to give an introduction to young onset dementia. It’s for anyone who might be worried about themselves or somebody else.
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This information was updated in March 2022 and is due to be reviewed in March 2024, it was written by Alzheimer’s Research UK’s Information Services team with input from the Young Dementia Network and lay and expert reviewers. Please get in touch if you’d like a version with references or in a different format.
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