What kind of dementia is hereditary? In the majority of cases, dementia is not inherited from a family member but is a result of other factors such as age, lifestyle and medical history. In a small number of cases however, dementia is inherited as a result of a ‘faulty gene’.
‘Familial’ or ‘young-onset inherited’ Alzheimer’s disease
Although having Alzheimer’s disease in the family can very slightly increase the risk of future generations getting the disease, in the majority of cases the biggest risk factor for Alzheimer’s disease is age.
However in a very small number of cases (less than 1%) Alzheimer’s disease is hereditary, passed down by a faulty gene from an affected parent. In these cases the disease usually develops at a much earlier age and is known as either ‘familial’ or ‘young-onset inherited’ Alzheimer’s disease. People with the affected gene will go on to develop Alzheimer’s and their children have a 50% chance of inheriting the gene and developing the disease.
The majority of cases of vascular dementia are not hereditary but happen as a result of a stroke or damage to the blood vessels in the brain. So while we may carry genes that increase our risk of developing heart disease or a stroke, lifestyle is often the biggest risk factor to developing vascular dementia.
However there is a rare form of vascular dementia caused by faulty genes, known as CADSIL (cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy), which can be passed down through families.
Lewy body dementia
Research into whether gene mutations play a role in Lewy body dementia is ongoing.
However, recent studies have shown that a gene associated with a completely different disorder, Gaucher’s disease, may influence a person’s susceptibility to developing a Lewy body disease as many of the same genes and proteins are involved.
Although for many people with frontotemporal dementia (FTD), the cause is not known, in around a third of people it can be triggered by a genetic problem known as ‘familial FTD’.
There are 3 types of frontotemporal dementia:
- Behavioral variant FTD (bvFTD), which is the most common form of FTD, is the type that is inherited most often, with up to half with a family history.
- Semantic dementia (SD), in contrast, is only rarely inherited.
- Progressive nonfluent aphasia (PNFA), in some cases can be due to a genetic disorder and run in families.
Huntington’s disease is caused by mutations in the HTT gene and is a progressive brain disorder that causes uncontrolled movements, emotional problems and problems with thinking (cognition). A persons mental abilities generally decline into dementia i.e. they become severe enough to affect daily life. Huntington’s disease usually appears in a person’s 30s or 40’s but more rarely appears in adolescence.
Huntington’s disease is typically inherited from a person’s parents. A parent with the Huntington’s disease gene has one good copy of the gene and one faulty copy. Their child will inherit one of these genes. Therefore, there’s a 50:50 chance that the child will get the faulty gene and develop Huntington’s disease.
In around 3% of cases of Huntington’s disease, there’s no obvious family history of the condition. This could be due to adoption or because relatives with the condition died early from other causes. In rare cases, it’s due to a new expansion in the gene.