What’s the point of a blood test for Alzheimer’s?

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By Kirsty Marais | Monday 17 March 2014

This time last week brought news of a potential blood test for Alzheimer’s, capable of detecting the disease before symptoms appear. Nearly every national newspaper carried headlines about the research, and our spokespeople were called on to help explain the implications of the study – and its limitations – for several broadcast stations.

Efforts to detect Alzheimer’s at this early stage have been ongoing for some time, with various approaches being tried in labs across the world. But we’re often asked what advantage there would be to such a test. Current treatments for Alzheimer’s are designed to help with the symptoms – so why would we need to diagnose the disease before those symptoms appeared? The answer lies in the search for new treatments.

Treating the disease early

It’s clear that we need much better treatments for people with Alzheimer’s, ones that can slow or stop the underlying disease process. Several drugs have been tested in clinical trials but so far, none have been able to improve thinking and memory. These trial results were disappointing, but as our Director of Research argued previously, they could hold the key to future success.

Crucially, the evidence now tells us that one of the key processes being targeted by many new drugs – the build-up of a protein called amyloid – occurs years before people develop symptoms. In fact, by the time people with Alzheimer’s begin to experience problems such as memory loss, much of the damage from amyloid may have already taken place. Current thinking suggests that to successfully stop amyloid accumulating, we need to intervene early. As last week’s BBC report on the latest findings explains, many researchers think previous drug trials may have failed because people were treated too late.

Catch 22

This leaves us with something of a ‘catch 22’ conundrum. If amyloid build-up has peaked by the time symptoms appear, the most logical time to test anti-amyloid drugs would be before symptoms show. But it’s not possible to test an Alzheimer’s drug in someone without symptoms unless you can be sure they’re in the early, pre-symptomatic stages of the disease. To overcome this challenge, we need an accurate, reliable way of distinguishing between these people and people who won’t go on to develop the disease. A blood test could be a neat solution.

Early detection or early diagnosis?

Of course, if such a test was possible, there would be a number of ethical questions to consider, and we’d need to tread very cautiously before using a tool like this in the general population. The test that hit the headlines on Monday is not available from your doctor, and it’s not being developed for that purpose. At the moment we don’t have evidence that screening – widespread testing of people without memory complaints – would be worthwhile. Instead, the drive to detect Alzheimer’s ahead of symptoms is about trying to better understand the disease, and identifying people who could be recruited for clinical trials.

That said, diagnosing Alzheimer’s is a tricky task for doctors, especially when someone still has only mild symptoms. Many people tell us that they, or their loved ones, have struggled to get a diagnosis to explain what’s causing their symptoms. A test to help doctors confirm a diagnosis for people experiencing memory problems would be a real advantage, not least in helping them access the right care and support as early as possible. Research into early detection could also feed into efforts to improve diagnosis tools available to doctors, for use when symptoms emerge.

Whether this latest test will turn out to be the tool we need remains to be seen, but many researchers are also focusing their efforts on this challenge. At Alzheimer’s Research UK we’re funding several projects using different approaches to improve early detection of Alzheimer’s – we’re optimistic that this research could give a real boost to the search for new treatments.


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Kirsty Marais