A new blood test, recently arrived in Brazil, could help in the diagnosis of Alzheimer’s disease. Using technology that identifies small molecules in blood samples, the procedure can observe the presence of an important disease marker.
Alzheimer’s disease presents with symptoms such as memory loss and difficulty performing daily activities, as it is associated with degeneration of the central nervous system.
The disease is the most common type of dementia in the world. In Brazil, it affects about 1.2 million people and affects about 11% of the elderly population, which is the most affected by the disease.
Regarding mortality, the Global Burden of Disease (GBD) 2019 points out that Alzheimer’s disease and other dementias represent a rate of 25 deaths per 100,000 inhabitants in the country.
Diagnosis is made mainly by clinical practice. In this way, the doctor investigates, in the face of symptoms and tests, if a person really has Alzheimer’s disease. Some research, for example, has already advanced to understand the causes of disease in order to increase diagnostic accuracy.
One of the most consolidated currents on the origin of the disease is interested in two proteins considered as markers of Alzheimer’s disease, that is to say substances associated with the disease.
One of these proteins is beta-amyloid, which is normally found in the walls of neurons, cells important for brain function.
Rodrigo Carvalho, a neurologist at the DFVNeuro Neurosurgery Center and Sírio-Libanês Hospital, explains that in excess, beta-amyloid is deposited in brain tissue.
“One of the hypotheses is that this protein deposit begins many years before the onset of Alzheimer’s symptoms. This already places this protein as a pathological marker of the disease”, he specifies.
This buildup of beta-amyloid triggers the retention of another protein, called TAU. It is the latter that causes the death of neurons and, therefore, causes a degenerative process of brain activity.
Thus, both proteins are associated with Alzheimer’s disease. This discovery means that “the tendency is more and more to classify the disease according to these substances which are altered”, continues the neurologist.
There are already tools that seek to observe these two markers. One of them is the collection of cerebrospinal fluid, a fluid that permeates the region of the brain and the lumbar spine. Because it is in constant contact with the region of the central nervous system, it is possible to observe the concentration of beta-amyloid by the CSF.
This procedure is performed by a doctor who inserts a needle between the vertebrae of the spine. Then, it is possible to take the cerebrospinal fluid to perform an examination to check for the presence of beta-amyloid. The lower the concentration of the protein, the greater the indication for Alzheimer’s disease, as it is an indication that the substance must be retained in the walls of the brain.
Although it is a useful procedure to complete clinical suspicions of Alzheimer’s, CSF collection presents some problems. One of them is the price – when performed by a doctor, the test is more expensive than other more common ones. Another point concerns certain contraindications, as in the case of patients who have an infectious process on the skin or have spinal problems that make it difficult to apply the injection.
The new test, launched in the United States a little over a month ago and which is made available in Brazil by the Dasa network of hospitals and laboratories, tries to break these impasses.
It works similarly to CSF collection by measuring beta-amyloid to see if the patient has Alzheimer’s disease. Because it’s a blood test, however, it required some changes that rely primarily on a technological advancement called mass spectrometry.
Gustavo Campana, medical director of Dasa, explains that observing the amount of protein in cerebrospinal fluid is easier because the fluid is in constant contact with the brain, an area that has the highest concentration of beta-amyloid. .
However, research has already observed that certain proteins can pass from alcohol to blood, but in smaller quantities – a phenomenon known as the blood-brain barrier.
For this reason, a common blood test would not have the same accuracy in indicating beta-amyloid concentration as in the CSF removal procedure. Spectrometry, in this case, is used precisely because it makes it possible to observe proteins, even in small quantities, in a blood sample.
“It’s a technology that allows me to separate different molecules to observe their concentration,” says Campana.
The test is not for everyone Although it is an important way to increase the accuracy of the diagnosis of Alzheimer’s disease, the new blood test is not for everyone.
The restriction of the procedure occurs primarily because Alzheimer’s disease is a clinically diagnostic disease. That is, it uses other mechanisms as well as the specialist’s own assessment of the patient’s condition.
Carvalho says magnetic resonance imaging can be used to see if symptoms were caused by other illnesses that mimic Alzheimer’s disease, such as strokes.
“It’s not that everyone has to do it, but for some specific cases, diagnostic supplementation is essential,” says Campana.
One such case in which it might be useful to observe the presence of beta-amyloid is when the doctor suspects that the patient may have Alzheimer’s disease or frontotemporal dementia, another disease also caused by neurodegeneration.
In this impasse, explains Carvalho, it is important to have a more precise diagnosis because the treatment of Alzheimer’s disease can worsen frontotemporal dementia.