Dementia & Genetics: What's the Link?

In the UK dementia affects one in six people over the age of 80, while there are 40,000 people under 65 living with dementia. This means that in the UK there are currently 450,000 people coping with dementia.
 

A common question about dementia is whether or not it is hereditary. The fact is that a lot of diseases are hereditary, or can be, while other diseases are simply caused by lifestyle factors. Dementia is caused by diseases of the brain, which can be caused by a range of factors, including a person’s lifestyle choices, health, age, and genes.
 

Can dementia be inherited?
 

The answer is yes, dementia can be inherited, but that doesn’t mean that just because a direct parent suffers from dementia, that their children will too. Firstly, only some kinds of dementia are genetically linked, and secondly, just because a parent carries a certain gene, there is no guarantee that it will be passed on, or if it is passed on whether it will lead to dementia.
 

Each gene is made up of a particular gene code, with gene codes varying naturally across the population, which means that often two people have different versions of a certain gene. This is known as genetic variation. Usually, these small differences have no impact, but in some instances, they can slightly increase the risk of developing a certain disease, such as cancer, diabetes, or Alzheimer’s Disease - a form of dementia. Although having a gene that carries the risk of developing a certain type of dementia does increase the likelihood that a person will develop dementia, it does not guarantee it. The gene that is linked to dementia is apolipoprotein E (APOE).
 

As well as inheriting risky genes, a person can also inherit faulty ones. A faulty gene is a gene with a mutation that can potentially affect how a person’s body functions. Some genes can have a strong impact and can cause a certain disease to develop regardless of the other risk factors. Some forms of dementia can be caused by faulty genes, such as rare forms of Alzheimer's Disease and can be passed down through families.
 

Does a person’s lifestyle impact their dementia risk?
 

Studies have shown that one in three cases of dementia could be prevented if people took better care of themselves throughout life. According to the study behind this research, 47 million people are living with dementia across the globe, and it’s estimated that by 2020 this figure will reach 131 million people.
 

The study identified nine key risk factors for dementia, as well as how much they increase dementia risk by, these are:
 

• Hearing loss during mid-life - 9% risk.
• Failing to complete secondary education - 8% risk.
• Failing to seek early treatment for depression - 4% risk.
• Smoking - 5% risk.
• Not being physically active - 3% risk.
• Social isolation - 2% risk.
• Being overweight or obese - 1% risk.
• High blood pressure - 2% risk.
• Type 2 diabetes - 1%.
   

Each of these risks comes with a percentage which dictates how much this specific lifestyle factor increases a person’s dementia risk. Together, these risks add up to 35% - this increased risk is modifiable and is determined by lifestyle choices. Whereas, the other 65% of risk is non-modifiable and is determined by genetics and luck.
 

Dementia tends to be diagnosed later in life, with the exception of people suffering from early onset dementia. However, the brain changes associated with dementia begin to develop years before any symptoms are noticeable.
 

What else increases dementia risk?
 

Aside from genetics and lifestyle factors, there is one other risk factor for developing dementia, and that is having a serious head injury. Certain types of head injuries may increase a person’s risk of developing certain types of dementia later in life, such as Alzheimer’s Disease and Pick’s Disease.
 

The people most at risk of developing dementia due to a head injury are people who have been knocked unconscious for 24 hours or more. However, anyone who has been knocked unconscious at any time, also has a slightly elevated risk. Needless to say, a person’s risk is increased again if they carry the apolipoprotein E (APOE) gene.
 

Of course, just because some people who have a serious head injury go onto develop dementia, that doesn’t mean that everyone who has a head injury will do. There are ongoing studies investigating the link between serious head injuries and dementia, so hopefully, in the next few years, we will have a better understanding of what this link means.