One in four people over the age of 55 have a close relative diagnosed with dementia. Knowing that our genes – the DNA that holds the story of our bodies – can play a part in developing certain types of dementia, it is natural for us to be concerned about conditions being passed down through families.
Dementia, however, is caused by a complex disease, meaning our genes are not a direct cause of the illness. Taking this into consideration, what should we be aware of when dementia becomes a part of our family health history?
“The majority of dementia is not inherited by children and grandchildren, and in the vast majority of cases, Alzheimer’s disease is also not inherited,” says Dr Ahmeda Ali, GP with webdoctor.ie. “In most cases, vascular dementia itself is not inherited. However, the underlying health issues that sometimes contribute to this condition, such as high blood pressure or diabetes, may be passed on from one generation to another.”
While dementia is a general term for a range of conditions that cause damage to the brain — affecting memory, thinking, language and the ability to carry out everyday tasks — Alzheimer’s is the most common cause.
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In general, the earlier a person develops Alzheimer’s disease, the greater the chance that it is due to a faulty inherited gene
Age remains the most important risk factor for Alzheimer’s disease. “However, says Dr Ali, “because Alzheimer’s disease is so common in people in their late 70s and 80s, having a parent or grandparent with Alzheimer’s disease at this age does not change your risk compared to the rest of the population.
“That said, if somebody has developed Alzheimer’s at an earlier age, before they are 60, there is a greater chance that it may be a type of Alzheimer’s disease that can be passed on. In these cases, the condition is much more likely to have been caused by a faulty gene being passed down from parents to children. In general, the earlier a person develops Alzheimer’s disease, the greater the chance that it is due to a faulty inherited gene.”
Risk factors for early-onset dementia or young-onset Alzheimer’s include:
- Down syndrome and other learning disabilities.
- Parkinson’s disease — as many as half of people with Parkinson’s disease may develop dementia.
- Risk factors for cardiovascular disease for example stroke, heart attack and angina.
- A past history of stroke.
- A history of excess alcohol consumption.
- A family history of dementia. There is a small extra risk of getting dementia if you have a mother, father or sibling with dementia. Dementia also seems to run in some families, so there may be some genetic factors that can make someone more likely to develop dementia. We do know that a few of the more rare causes of dementia can be inherited.
- Severe psychiatric problems such as schizophrenia or severe depression. It is not clear why this is the case, and further research needs to be done.
- A past history of a head injury.
- Lower intelligence. Some studies have shown that people with a lower IQ level and people who do not have very high educational achievement are more likely to develop dementia.
- A limited social support network.
- Low physical activity levels. A lack of physical activity can increase your risk of dementia.
Rarer types of dementia, such as Huntington’s disease and Familial Prion disease, can also hold a strong genetic link, but these are only a tiny proportion of overall cases of dementia.
“These diseases have a 50-50 chance of being passed on, because they are caused by a single faulty ‘dominant’ gene,” says Dr Ali. “This means that if you inherit a healthy gene from one parent and a faulty gene from the other parent, the faulty gene will always be the one that is used because it’s the ‘dominant’ gene.”
Frontotemporal dementia (FTD) is relatively rare in comparison to Alzheimer’s disease or vascular dementia, but it comes with an increased possibility of being passed on directly from parent to child, which can cause significant worry for families when diagnosed with FTD.
“Most FTD is not directly inherited,” says Dr Ali, “but about 40 per cent of people who develop the condition will have at least one close relative diagnosed with some kind of dementia. This can include FTD, Alzheimer’s disease or amyotrophic lateral sclerosis (ALS), sometimes known as motor neurone disease.
“In general, the greater the number of relatives who have had dementia — particularly FTD or ALS — the greater the chances of developing ‘familial’ FTD.”
More than half of people will never develop dementia even if they reach the age of 95. But dementia is not a normal part of ageing
Dr Ali advises that the World Health Organisation (WHO) says there are about 50 million people in the world with dementia, with nearly 10 million developing the condition each year.
“The likelihood of getting dementia increases with age,” she says. “Having said that, more than half of people will never develop dementia even if they reach the age of 95. But dementia is not a normal part of ageing. It is different to the age-associated memory impairment that is common in older people.”
Having risk factors for cardiovascular disease can also increase your risk of developing all types of dementia. These risk factors include smoking, raised cholesterol levels, drinking too much alcohol, not doing enough physical activity, being overweight, and having diabetes or high blood pressure.
“It would seem likely that doing something to modify these risk factors may reduce your risk of developing dementia,” says Dr Ali. “Stopping smoking, reducing excessive alcohol, and losing weight if you are overweight, for example, may all help to reduce your risk of dementia.
“Regular physical exercise is advised for all sorts of health benefits, including reducing the risk of dementia. One UK study suggested that a fifth of cases of Alzheimer’s disease might have been related to a lack of physical activity. It proposed that regular exercise might have prevented some of these cases. Keeping your brain active may also help to reduce your risk of developing dementia. So, for example, consider reading books, doing puzzles, learning a foreign language, playing a musical instrument etc.”
If you suspect early-onset familial dementia or Alzheimer’s, Dr Ali advises that the first step is to see your doctor. “He or she may suggest some special tests to look at your memory and mental ability, to see whether dementia is likely or not,” she says. “This does not take long, and is usually a series of questions or other exercises that your doctor asks you to complete.”
While studies regarding treatments and preventions are ongoing, including certain blood pressure medicines, omega-3 fatty acids, brain training exercises and the strategies listed above, Dr Ali advises that there is not yet convincing evidence available for any of these, and further research is needed.
In the meantime, we can continue to collect as much information as possible regarding our family health history, and look at our lifestyle choices and the environmental factors that play a part in the possibility of developing dementia, and making adjustments where needed.
