In a scientific article published on December 27, researchers claim to have devised a blood test for the diagnosis of Alzheimer’s disease, which might only be confirmed by two expensive techniques, one of which is quite invasive. This easy-to-use test might therefore allow many patients to start treatment earlier.
Because beta-amyloid and tau proteins accumulate abnormally and clump together in the brains of people with Alzheimer’s disease, confirming the diagnosis involves measuring their abundance in the brain using a sophisticated cerebral imaging technique, as well as their abundance in the cerebrospinal (or cerebrospinal) fluid, in which the brain and spinal cord bathe, through a lumbar puncture which aims to collect cerebrospinal fluid in the surrounding space the spinal cord using a needle that is inserted into the back, between two vertebrae.
“Some of the excessive amounts of tau proteins that are released by damaged nerve cells in the brain diffuse into the cerebrospinal fluid. However, there are far fewer beta-42 amyloids in this fluid, in people with Alzheimer’s, because these proteins remain stuck in the brain, which cannot get rid of them. The senile plaques that we see under the microscope are precisely deposits of insoluble amyloid,” explains Dr.r Serge Gauthier, Director of the Alzheimer’s Disease and Related Disorders Research Unit, McGill Center for Studies in Aging.
Reliable and accurate diagnosis
Lumbar puncture is a delicate, painful procedure and not recommended for people taking anticoagulants. In addition, positron emission tomography, which makes it possible to visualize tau proteins in different regions of the brain, which was developed in Montreal, is very expensive: $5,000 per examination. “These two tests are reimbursed by the Régie de l’assurance maladie du Québec. But you have to send the cerebrospinal fluid samples to Amsterdam, Europe, or to a commercial laboratory in the United States,” says Dr.r Gautier.
The advantage of a blood test is that it will be less expensive (between $400 and $500) than a tomographic examination ($5000) and less invasive than a lumbar puncture
However, researchers from the University of Gothenburg, Sweden, the University of California, San Diego, the University of Pittsburgh and the University of Brescia, Italy, describe in the journal Brain a blood test that detects the particular form of tau protein that builds up in the brains of people with Alzheimer’s disease.
Current blood tests detect tau proteins from all over the body. To differentiate brain-derived tau proteins from others, researchers have developed antibodies that specifically recognize the tau protein associated with Alzheimer’s disease.
The scientists tested their test in 600 patients with different stages of Alzheimer’s disease, and they found that the levels of brain tau protein measured in the blood of these patients by their test corresponded well to those measured in the cerebrospinal fluid. . Protein levels were also proportional to the severity of amyloid plaques and tau protein tangles in the brains of people who died of Alzheimer’s. In addition, the test reliably distinguishes Alzheimer’s disease from other neurodegenerative diseases.
A promising test
The Dr Gauthier is delighted with this progress in the development of blood tests allowing a reliable and precise diagnosis. “The advantage of a blood test is that it will be less expensive (between $400 and $500) than a tomographic examination ($5,000) and less invasive than a lumbar puncture. And what’s particularly encouraging regarding this article is the fact that some of the techniques the researchers used are already on the market, which brings us one step closer to a blood test that might be used in the clinic. And I can tell you that the National Institute for Excellence in Health and Social Services is very interested in this kind of diagnostic test. So such a test might become available quickly in Quebec,” he says.
“In three years, when we have completed the clinical trials [visant à évaluer de nouveaux traitements] and that we will have found some effective drugs, hopefully, we will be able to follow up these patients with blood tests, a bit like we do for prostate cancer following radiotherapy or chemotherapy, by measuring prostate-specific antigen in the blood. This would make it easier to monitor the effect of new treatments,” he argues.
But before we get there, the test will have to be tested on a larger number of patients. “We might also see if we can detect the disease before the onset of symptoms, by evaluating the test in people who carry one or more genes for the familial form of the disease, because we know that these people will certainly develop the disease. “says the Dr Gautier.