Do tests really detect Alzheimer's disease before symptoms appear?

Do tests really detect Alzheimer's disease before symptoms appear?

New YorkKnowing whether a person has Alzheimer's disease is always a very slow process. Symptoms are analyzed, cognitive, visual, and verbal tests are performed, and a positron emission tomography (PET) scan, MRI, or lumbar puncture may be performed to detect the presence of two proteins in the brain: amyloid plaques and TAU. Buds associated with dementia. The scientific community has long called for changing the criteria for defining disease to stop placing so much weight on behavior and take into account biomarkers that indicate the presence of disease before symptoms appear.

Two events accelerated everything. For one thing, blood tests to detect amyloid have been shown to be more accurate and less invasive than a lumbar puncture, and much less expensive than brain scans. On the other hand, drugs that can remove amyloid from the brain have emerged after they were shown to have a moderate, but significant, ability to reduce the progression of symptoms over 18 months in cases of mild Alzheimer's disease. However, are these advances sufficient to diagnose healthy people with irreversible disease?

“If you have an amyloid biomarker in the brain, you have the disease, whether you have symptoms or not,” says Clifford R. Jack Jr., head of the Alzheimer's Disease Task Force and a Mayo Clinic researcher. “The pathology is there years before symptoms appear. “This is irrefutable,” he adds. Now, while some researchers believe the diagnosis would likely be made anyway, others advise against testing people without symptoms of cognitive impairment. How many people with amyloid deposits or TAU will develop dementia? “It depends,” says Jacques. A Dutch study suggested that more than 10% of people without cognitive impairment aged 50 or older will test positive for this condition. type tests, and the same will happen to about 16% of adults aged 60 and 23% of adults over 70. However, almost none of these individuals will develop dementia.

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Conflict of interest allegations

Another Mayo Clinic study followed 5,000 older adults who had normal cognitive levels for nine years. Thus, they discovered high rates of dementia among those who carry the APOE4 gene, which is associated with an increased risk of developing Alzheimer's disease. For those over 65 with high levels of amyloid, the risk of dementia rose to 74% in women and 62% in men. However, according to the National Institute on Aging, only 15% to 25% of the population has this gene. Among those without it, both women and men had an estimated risk of 55% with high levels of amyloid and 36% with moderate levels.

“I think the evidence that amyloid per se determines Alzheimer's disease is still not clear or convincing,” says Jason Karlawich, MD, a geriatrician and co-director of the Mental Health Clinic at the Penn Memory Center. Like him, many specialists remain unconvinced about the use of these tests in general. The North American Geriatrics Society also calls the standards premature and points to relationships between researchers and the pharmaceutical and biotechnology industries, citing potential conflicts of interest.

Eric Widera, a geriatrician at the University of California, points out that about a third of researchers who advocate for biomarkers work for companies that make drugs or screening tests, with grants, contracts, fees or consulting fees. “This change will have direct benefits for them,” he adds. In this regard, he says, about 40 million cognitively normal Americans could test positive for amyloid, be diagnosed with Alzheimer's disease, and begin treatment with unapproved drugs. In general, the geriatrician adds, it frightens them unnecessarily because they are less likely to develop dementia.

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