Genes play a role in the development of many types of dementia, although the extent of this role varies between dementia types. A person with a parent or sibling with a dementia such as Alzheimer’s disease has on average a higher risk of developing the same condition themselves, although other factors such as lifestyle can also play a part.
At present, the relationship between genetics and dementia is not fully understood. We do know that a mutation (change) in one of a small number of genes can cause someone to develop frontotemporal dementia or rarer, inherited forms of Alzheimer’s disease. These conditions both often start in people under the age of 65.
Predictive genetic testing is where the genes of someone who is related by birth to a person with diagnosed dementia are tested. The genetic test aims to see whether the relative has inherited the same mutation and so will go on to develop the dementia. At present such predictive genetic testing is only possible for inherited Alzheimer's disease, in which very rare mutations in three genes are implicated, and frontotemporal dementia, which has known mutations in at least six genes. The most common form of Alzheimer’s disease affects about 520,000 people in the UK and most often starts in people over the age of 65. There are no approved predictive genetic tests for this form of the condition.
In the vast majority of people, any genetic risk of Alzheimer’s disease - increased or decreased - is linked not to rare mutations but to variations in a large number of susceptibility genes that they have inherited. The most common risk gene is called APOE. This gene has a number of variants, and a variant called e4 has been shown to increase risk of developing Alzheimer’s disease. However, risk genes such as APOE have a more subtle influence on someone’s chances of developing Alzheimer’s disease than the genes that are used in tests for the inherited forms of dementia.
Predictive testing for APOE variants outside of approved research studies is currently available in the UK only on a commercial basis: for a fee, companies not based in the UK will analyse a saliva sample sent off in the post. However, the results of APOE testing have low predictive value. Someone who has two copies of the higher risk APOE variant e4 is not certain to develop Alzheimer’s disease, while someone who has other variants still might. This poor predictive value is why APOE testing is not recommended (outside research studies) or available within the NHS.
Genetic testing can be difficult emotionally, not provide conclusive results and cause practical difficulties. Before considering genetic tests, it is vital that proper genetic counselling is provided to ensure it is the correct decision for the individual. It is also vital that, if someone does have testing, they receive full genetic counselling about what the results mean. No counselling is currently provided with the commercially available APOE test.
For more information on genetic testing, please see factsheet 405 Genetics of dementia.
Alzheimer's Society strongly believes that there should be legal protection against discrimination on the grounds of genetic information. There is currently a moratorium on the use of genetic information by UK insurance companies until November 2019. Alzheimer’s Society campaigns for the continued prevention of insurers and employers using genetic information to discriminate against people at risk of dementia.
2. What Alzheimer's Society calls for
- Proper and timely genetic counselling for all individuals who choose to consider predictive genetic tests. There are no approved predictive genetic tests for the most common form of Alzheimer’s disease. However, regional genetics clinics offer testing for people whose family history of dementia suggests they might carry one of the causative mutations for inherited Alzheimer’s or frontotemporal dementia. It is important to note that testing can be difficult emotionally, not provide conclusive results and cause practical difficulties. Before this test, it is vital that proper genetic counselling is provided to ensure it is the correct decision for the individual. For more information, please see our page: Genetics of dementia.
- Continued prevention of insurers using genetic information to discriminate against people at risk of dementia in the future. People receiving a positive result in a genetic test can face discrimination that affects their ability to buy property, get insurance or plan financially for old age. There is, however, a moratorium on the use of genetic information by UK insurance companies until November 2019. Alzheimer’s Society campaigns for the continued prevention of insurers and employers using genetic information to discriminate against people at risk of dementia.
- Research into the genetic risk factors for dementia. Progress in genetics has meant that more than 20 susceptibility genes have been identified that affect a person’s risk of developing Alzheimer’s disease. The genetic basis of frontotemporal dementia is also a very active research field. These conditions are now the subject of intense scientific investigation. Ultimately, this research may identify causes of the disease. Alzheimer’s Society supports, and funds, genetic research.