When someone in the family gets dementia, close relatives worry about whether they will get dementia, too. Genetic risk of dementia is a focus area for researchers. Concerned persons can get a correct overview of the current understanding by checking authoritative, up-to-date sites. This page includes some excerpts and suggested links.
The position paper of Alzheimer’s Society, UK, on genetic testing explains the current understanding of the genetics of Alzheimer’s Disease and other forms of dementia.
Here are a few excerpts from some relevant authoritative pages. These have all been reconfirmed in March 2022.
Sometimes, a gene changes and this causes a disease. This is known as a single-gene disease because it is caused by a change in just one gene. Single-gene diseases are often serious, but they are rare. 
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…..
…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.
Most people with Alzheimer’s have the late-onset form of the disease, in which symptoms become apparent in their mid-60s and later.
Researchers have not found a specific gene that directly causes late-onset Alzheimer’s disease. However, having a genetic variant of the apolipoprotein E (APOE) gene on chromosome 19 does increase a person’s risk.
Early-onset Alzheimer’s disease is rare, representing less than 10 percent of all people with Alzheimer’s. It typically occurs between a person’s 30s and mid-60s. Some cases are caused by an inherited change in one of three genes…..
Mutations in these genes result in the production of abnormal proteins that are associated with the disease. Each of these mutations plays a role in the breakdown of APP, a protein whose precise function is not yet fully understood. This breakdown is part of a process that generates harmful forms of amyloid plaques, a hallmark of Alzheimer’s disease.
The majority of dementia is not inherited by children and grandchildren. In rarer types of dementia there may be a strong genetic link, but these are only a tiny proportion of overall cases of dementia.
The genetic links differ for different types of dementia., and the discussion on the page Is dementia hereditary? explains these different risks.
You can get genetic counselling to know whether you are at higher than normal risk for dementia. This will help you see whether you should consider genetic testing (this is not available easily in India). One factor is considering whether the results of such testing would make a difference to how you plan your life. More links to understand genetics and related decisions are provided below.
Documents referred to above:
-  Position paper of Alzheimer’s Society, UK, on genetic testing: Alzheimer’s Society’s view on genetic testing Opens in new window.
-  Alzheimer’s Society, UK: Genetics of dementia Opens in new window.
-  National Institute of Aging, USA: Alzheimer’s Disease Genetics Fact Sheet Opens in new window.
-  Alzheimer’s Society, UK: Is dementia hereditary? Opens in new window.
- Genetic Testing (from Alzheimer’s Association, USA) (PDF file) Opens in new window.
- Risk factors: Genetics (heredity)(from Alzheimer’s Association, USA) Opens in new window.
- Alzheimer’s Disease Genetics Fact Sheet (from National Institute of Aging, USA) Opens in new window.
This page is referred to from: Diagnosis, Treatment, Prevention.
[The information on this page is a collation from standard, authoritative sources, provided only for convenience. Caregivers can check out these and other sources to get better informed about this topic.]