Written by Ryan on Wednesday the 31st of January 2018.
For many people who have had a family member diagnosed with dementia, it is natural that they question whether dementia is hereditary. Unfortunately, whilst huge in-roads have been made in understanding the role genetics play in dementia, we still have a great deal more research to undertake until we truly understand the impact.
However, whilst research is still ongoing, we do have some understanding of how different types of dementia are affected by different types of gene mutations, and thus whether there is a higher probability of inheriting the disease.
For some of these inherited genes, genetic testing is available to family members. However, due to the emotional impact discovering a genetic fault can have, family members generally need to undertake genetic counselling before the tests are taken. It is also important to know that even if you or a loved-one discovers they have a dementia-related gene, depending on the type, it does not necessarily mean that you or they will develop dementia.
Early On-Set Alzheimer’s
The causes of early on-set Alzheimer’s are still relatively unknown, however researchers have discovered that a very small number of people diagnosed with the condition have inherited the gene. Currently only three of these genes are known; amyloid precursor protein, presenilin 1 and presenilin 2, though there may be more that have yet to be discovered.
Early on-set Alzheimer’s caused by this gene is often referred to as early on-set inherited or familial Alzheimer’s. This faulty gene can affect many members of the same family, and it doesn’t skip generations.
Genetic testing, in the form of a blood test, is available on the NHS for someone with suspected inherited early on-set Alzheimer’s. Generally, as the on-set gene is carried in a family, the whole family should be involved in the discussion about the testing, and should the gene be found then ideally all direct relations should also be tested.
Late On-Set Alzheimer’s
There is still a lot to understand about how genetics affects late on-set Alzheimer’s, as it often develops due to a combination of risk factors, such as age (generally people over the age of 65 are more likely to get a diagnosis) and lifestyle (such as smoking).
Currently, 20 versions of the gene have been found that could cause a higher chance of developing late on-set Alzheimer’s. The most well-known risk gene is called APOE, which makes protein that keeps our brains healthy. APOE is divided into 3 versions, APOE2, APOE3, APOE4.
A person who has one APOE4 gene is about 3 times more likely to develop Alzheimer’s. However, a person who inherits 2 copies, one from each parent, can be 8 times more likely to develop the disease. But, even with both copies of APOE4 present, the development of late-set Alzheimer’s may still not ever occur. Due to the uncertainty of the gene’s impact, genetic testing is not available on the NHS.
Vascular dementia generally occurs as a result of a stroke or damage to a blood vessel in the brain which causes blood flow to reduce. Generally, vascular dementia is not hereditary, however, genes that can cause strokes or other diseases that may contribute to vascular dementia may be present.
Frontotemporal Dementia (Pick’s Disease)
Pick’s disease is a very rare form of dementia, generally affecting younger people. About 10-20% of all frontotemporal dementia cases are thought to be hereditary. These cases can be caused by one of a number of faulty genes, including; tau, progranulin and C9ORF72.
When a tau gene mutates it can cause the tau protein to form clumps on the brain, which damages the cells, leading to frontotemporal dementia. Whilst scientist know that mutations of progranulin and C90RF72 can lead to frontotemporal dementia, more research needs to be done to truly understand the impact.