What is Alzheimer's disease?

And what might be the cause of it?
26 March 2024

Interview with 

Susan Kohlhaas, Alzheimer's Research UK


What is going on in the nervous system to cause Alzheimer’s Disease? Susan Kohlhaas is from the charity Alzheimer’s Research UK…

Susan - So Alzheimer's disease is a fairly common disease actually, and it's the most common cause of something called dementia. So the word dementia is used to describe a group of symptoms that include things like memory loss, confusion or difficulties with communication. And Alzheimer's disease is one thing that can cause dementia. Around six in every 10 people with dementia in the UK have Alzheimer's disease.

Chris - Who's most at risk?

Susan - There are a different number of factors associated with Alzheimer's disease. So there are people who are genetically at risk of dementia. And then around 40% of cases of Alzheimer's disease can be put down to what we would call modifiable risk factors. So things around lifestyle or environment that can influence somebody's risk of developing dementia. So we have things like air pollution, smoking, or diet that are influencing somebody's risk of developing Alzheimer's disease as well.

Chris - And because they live longer than men, on average, are women more at risk or if everyone reaches the same age as it roughly even stevens between men and women?

Susan - Interestingly, more women develop Alzheimer's disease and other diseases that cause dementia than men. And when they control for things like age, actually that doesn't explain the difference. So women do seem to be at greater risk of developing Alzheimer's disease than men, regardless of whether they live to longer ages or not. And we don't quite fully understand why that is.

Chris - But what is going on? If we look at the brain of someone with Alzheimer's disease, what do we see and why do we think we're seeing that?

Susan - We see a lot of differences between the brain of somebody living with Alzheimer's disease and somebody without it. And I think one of the really important things to say is that Alzheimer's disease is not an inevitable part of ageing. You get people living to a hundred years old without any signs or symptoms of Alzheimer's disease. It's also one of these diseases where the brain changes start to happen kind of 15, 20 years before you actually see symptoms. So it's a really challenging disease to study for that reason. But what happens in the brain is that you get a buildup of certain types of proteins called amyloid that start to clump in the brain, and then that causes some further proteins such as proteins called tau to make tangles in the brain. And then that can cause a toxic environment for brain cells, and then they start to die. There's some more work to do that's looking at the role of things like immune cells in the brain and whether neuroinflammation can actually cause problems as well. So not only is there a buildup of proteins in the brain that are thought to be causing a toxic environment, there's also other mechanisms and cell types in the brain that seem to be going awry in Alzheimer's disease. And the challenge is to unpick all of that to develop new treatments.

Chris - These proteins that build up pathologically, what's their normal role then? Why are they there? Why do we have something that can become bad in some people?

Susan - So we don't really know exactly what happens to trigger the buildup of proteins like amyloid. There is some work to suggest that the role of these proteins when they're functioning normally throughout life can give some advantage to people. So the role of some of the genes that are associated with risk of Alzheimer's disease can actually be helpful in terms of navigation earlier on in life. There is still a lot more to learn in terms of the function of all of these proteins and what they do. What we do know is that in Alzheimer's disease, for some reason, they start to build up. And that could be because the immune system that's normally responsible for clearing proteins in the brain just isn't quite clearing them as quickly. Could be that there's something triggering that's happening that's causing this buildup. And there's a mixture, again, of environment and genetics that seems to be causing this.

Chris - If we look at how many people are affected by this now, and we look at the changing population demographics, what do we think the picture looks like in say, 30 years time?

Susan - At the moment, there are around 800,000 people who have Alzheimer's disease in the UK. But we think that this figure actually is probably an underestimate because many people, around a third of people living with dementia, never actually receive a diagnosis at all. And data on who gets diagnosed and where, is frustratingly just incomplete. So it makes understanding dementia and dementia care a huge blind spot for our healthcare decision makers and our wider politicians. We know that age and ageing is one of the top risk factors for developing Alzheimer's disease. And we also know that dementia in the UK is our biggest killer. So nearly 75,000 people died of dementia in 2022. So without any change, we expect the number of people with Alzheimer's disease to grow and we expect it to become much more costly to deal with the effects of dementia as well. So we really do need to do as much as we can now to find new treatments and ways to diagnose dementia better and also ways to prevent it.

Chris - And what are those effects? How would we recognize someone who's affected and what can we do better to support them?

Susan - The difficulty is that Alzheimer's disease and wider dementias affect everybody slightly differently because their brain diseases and the brain is such a dynamic organ and it's such a sort of key organ to anything that we do. So how we think, feel, behave, everything in Alzheimer's disease, you can start to see issues with navigation. You start to see memory and thinking problems that can crop up and then move away. You can start to see personality changes as well. And what we would always say at Alzheimer's Research UK is if you have any concerns about you or a loved one, please do go and see a GP in in the first instance because they can start to rule out things that it might be or also start to get you referred into a memory clinic in order to see whether you have Alzheimer's disease or other dementias, which would give you access to care and research that you wouldn't otherwise have.


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