Detect disease through blood test, a revolution but for what purpose?

For years, it has been one of the main axes of research into this disease, the most common form of dementia, which irreversibly affects millions of people in the world. The idea is to be able to identify, through a simple blood test, the manifest signs of the physiological mechanisms by which the disease takes hold. We know two main mechanisms, without fully understanding their interaction: the formation in the brain of so-called amyloid protein plaques, which compress and eventually destroy neurons; and the accumulation of another protein, called tau, within the neurons themselves.

Important progress

Examinations already exist: by lumbar puncture or by a medical imaging technique, positron emission tomography (PET). But because they are long, heavy and expensive, many patients are stuck with clinical findings, such as severe memory loss. Some blood tests are already marketed but, in fact, the remaining data on their actual benefit are little used. However, in recent months, several studies have shown the effectiveness of certain blood tests to detect internal signs of the disease. The most notable dates in the JAMA Neurology journal are January.

Conducted by following nearly 800 people, it was concluded that the blood test makes it possible to identify abnormal amounts of amyloid or tau with an effectiveness comparable to the tests currently in place. Crucially, this test is useful at the “preclinical” stage, before the typical symptoms of the disease appear. The medical world generally welcomed the important step forward, despite the limitations. This effectiveness has to be confirmed in actual practice and, above all, such testing only points to the presence of physiological mechanisms that do not systematically result in dementia.

effective treatment

In a response to the Science Media British Center (SMC), neurologist Bart de Strooper said this was “an excellent study that puts us on the brink of being able to use a blood test for Alzheimer’s disease on a daily basis.” In the United Kingdom, this is already almost a reality. A program launched last year by several anti-Alzheimer’s organizations aims to test the benefit of these blood tests within the British healthcare system.

But for what? Without effective treatment, early diagnosis is of little benefit. However, many neurologists are now hoping that drugs may work. After decades of unsuccessful research, two treatments — one by the Eli Lilly lab, the other by Biogen — appear to be able to slow the progression of Alzheimer’s by attacking amyloid plaques. Their effectiveness is modest and side effects are serious, but for many neurologists, they are the first step toward other, more effective treatments.

Early diagnosis

In this regard, it seems promising to be able to identify Alzheimer’s disease as quickly as possible using a simple blood test to increase the effect of treatment. There remains a significant nuance. We are talking about an early diagnosis here, in patients already with impaired memory, and certainly not a screening that is aimed at just anyone. “Today, it makes no sense to test blood biomarkers in people who do not have cognitive deficits: it will only do harm,” emphasizes Giovanni Frisoni.