Is dementia genetic?

If your parents have been diagnosed with Alzheimer’s disease or another form of dementia, does that increase your risk of developing the disease at some point in the future?

Alzheimer’s disease is the most common form of dementia and is estimated to affect more than 520,000 people in the UK. Genes do play a role in the disease and if you have a parent, brother or sister with Alzheimer’s then you are at an increased risk of developing it in the future.

To date, scientists believe there are over 20 different genes that are linked to an altered risk of Alzheimer’s disease.

There are some more rare forms of dementia that have been linked to known changes in certain genes. These genes can be passed down in DNA across several generations. However, these genetic forms of dementia account for less than one per cent of all cases.

Developing Alzheimer’s disease under the age of 65 is known as early onset or younger onset Alzheimer’s disease. With early onset Alzheimer’s disease, about one in ten people have a strong family pattern of inheritance.

The more common form of Alzheimer’s disease, which is usually diagnosed after the age of 65, has a more complex relationship with genetics.

 

Screen Shot 2016-09-05 at 13.19.13Three genes

The inherited forms of Alzheimer’s disease are usually caused by a mutation in one of three genes, called APP, PSEN-1 and PSEN-2. The gene called PSEN-1 causes up to 80 per cent of what is known as ‘Familial Alzheimer’s disease’, where the disease affects generations of families. However, these mutations are rare. Fewer than one in 100 of all Alzheimer’s disease cases are thought to be caused by mutations in these three genes. However, if you do inherit a mutation in one of these genes it is likely that you will develop Alzheimer’s disease. A child of a parent with one of the three genes has a 50 per cent chance of developing it.

Alzheimer’s disease most commonly begins after the age of 65 (this is sometimes called late onset Alzheimer’s disease). The causes of this form of the condition are thought to be a mixture of genetic, lifestyle and environmental factors. A gene called apolipoprotein E (APOE) is the strongest known genetic risk factor for late onset Alzheimer’s. The gene has three forms – APOE e2, APOE e4 and APOE e3. APOE e4 is associated with an increased risk of Alzheimer’s disease.

You inherit one copy of each gene from each parent. Having at least one APOE e4 gene increases your risk of developing Alzheimer’s disease. Having two copies of APOE e4 (i.e. inheriting the gene from both parents) increases risk even further. However, not everyone who has one or two copies of this gene develops Alzheimer’s disease. Also if you have other versions of the gene – ApoE e2 or ApoE e3, it does not mean that you will not get Alzheimer’s disease.

There are a number of other genes that could be risk factors for Alzheimer’s disease and some researchers believe that several genes may work in combination to influence a person’s risk of dementia. However, more research is needed to understand the roles of these genes when it comes to dementia risk.

 

Age is the biggest risk

One thing we do know is that age is the single biggest risk factor for Alzheimer’s disease and vascular dementia. Above the age of 65, your risk of developing Alzheimer’s disease or vascular dementia doubles every five years according to Alzheimer’s Society. Dementia is estimated to affect one in 14 people over 65 and one in six over the age of 80.

Vascular dementia is caused by a stroke or series or mini-strokes leading to a reduced oxygen supply to the brain. It affects approximately 150,000 people in the UK. It is less likely to be genetic, though further research is needed. Studies have shown conflicting results, as some studies show links between the gene called APOE, which can play a role in development of Alzheimer’s disease, while others don’t.

 

Lifestyle may reduce risk

Lifestyle can play a role in reducing your chances of developing Alzheimer’s disease or vascular dementia. Things that are known to increase your risk of dementia include smoking, having high blood pressure and high cholesterol. Evidence shows that leading a healthy lifestyle, including eating a healthy, balanced diet (for example a Mediterranean style diet, rich in vegetables, fruit, cereals, legumes and with some oily fish and low in red meat and sugar) and exercising regularly can reduce your risk of dementia.

 

Healthy choices

The benefits of regular exercise for improved brain function were highlighted recently. According to research presented by Dr Laura Baker of Wake Forest University Health Sciences at the Alzheimer’s International Conference in Toronto in July, several trials showed that exercise slows brain shrinkage and boosts cognition (our ability to think, learn and understand).

A 12-week study showed that regular cardiovascular exercise thickened the cortex of study participants – the brain’s outer layer of neural tissue that plays an important role in our consciousness. It revealed that 45 minutes of cardiovascular exercise four times a week where people were working hard, showed decreased levels of tau – a protein that builds up in the brain that is thought to contribute towards the development of Alzheimer’s. The study also showed an increase in blood flow to the brain. While this data is promising, we need longer ‘gold standard’ trials to more fully understand the effects that exercise has when it comes to dementia risk.

 

Take care of your heart

‘A healthy heart generally means a healthy brain,’ says Dr Emer MacSweeney, CEO & Medical Director of brain health experts Re:Cognition Health (http://www.re-cognitionhealth.com). ‘Regular intense exercise four times a week has been shown to reduce Alzheimer’s risk in a recent study.’

‘Carefully conducted clinical trials have shown that the genes which are recognised to be responsible for cognitive impairment in Alzheimer’s disease become less effective in individuals who pursue a programme of relatively intense and sustained exercise, compared to a matched group of individuals who do not undertake this exercise programme.’

While we can’t control our genetics, being health conscious and taking regular exercise and eating a healthy diet are clearly lifestyle factors that we can control.