The NHS says that around 944,000 people living in the UK have dementia ― one in 11 over-65s, to be specific.
So if you’ve got an older loved one, including parents and grandparents, you might have had some first-hand experience with the condition.
Perhaps understandably, then, Alzheimer’s Society says that “Many people affected by dementia are concerned that they may inherit or pass on dementia.”
Luckily, however, they add that “The majority of dementia is not inherited by children and grandchildren,” though some rarer conditions are more strongly affected by your genes.
So what are the numbers?
Alzheimer’s Society says, “In the vast majority of cases (more than 99 in 100), Alzheimer’s disease is not inherited.”
Alzheimer’s Research UK agrees, saying that while “The likelihood of developing [dementia] will usually depend on a complex mix of factors... most cases of dementia are not directly caused by genes we inherit from our parents.”
They add that scientists have found about 75 genes associated with a heightened risk of developing Alzheimer’s but stress that “having one of these versions may only have a small effect on our overall risk.”
We still don’t fully know the role these genes play in the development of dementias, though APOE genes are the best understood and some variants seem to carry the largest Alzheimer’s risk.
“People who inherit one copy of APOE4 (roughly one in four people) are around three times more likely to develop late-onset Alzheimer’s disease. About one in 50 people inherit two copies of APOE4 – one from each parent. They may be more than eight times more likely to develop Alzheimer’s,” Alzheimer’s Research UK says.
Nonetheless, they state that even those with two sets of APOE4 genes from both parents may never develop the condition. “Late-onset Alzheimer’s is not directly inherited through faulty genes,” they end.
Different dementias have different risks
Young-onset Alzheimer’s is more heritable than late-onset Alzheimer’s: “If somebody has developed Alzheimer’s disease at an earlier age (for example, less than 60 years old) there is a greater chance that it may be a type of Alzheimer’s disease that can be passed on,” Alzheimer’s Society writes.
Other dementias, like Huntington’s Disease and Familial Prion Disease, can have a 50/50 chance of being inherited ― but thankfully these are far rarer than Alzheimer’s.
Nonetheless, Alzheimer’s Society UK suggests that “Having a test to look for a faulty gene that causes dementia is only appropriate for a very small number of people. This is because inherited dementia is rare.”
The most common cause of Alzheimer’s is still age; so your best defences against the condition seem to be to keep your lifestyle healthy by eating well, exercising, sleeping well, and trying to lower stress as much as you can.
If you suspect dementia in yourself or a loved one, speak to your GP as soon as possible as the condition is under-diagnosed despite benefiting from early intervention.
And as the NHS says, “If several of your family members have developed dementia over the generations, and particularly at a young age, you may want to seek genetic counselling for information and advice about your chances of developing Alzheimer’s disease when you’re older.”