Μake us preferred on Google Could millions of people be considered potential Alzheimer’s patients before showing any symptoms? Advances in blood testing and treatments targeting the disease’s biological mechanisms have brought that question to the center of a growing debate in the scientific community.
The controversy concerns preclinical, or asymptomatic, Alzheimer’s disease: a stage in which people show biological signs associated with the condition but have no apparent cognitive decline. For some researchers, identifying these changes years or even decades before symptoms emerge could open the way to earlier intervention and, potentially, dementia prevention. Others warn that this approach risks labeling healthy people as patients without knowing whether they will ever develop the disease.
Until recently, Alzheimer’s diagnosis relied primarily on the progressive deterioration of memory and other cognitive functions. Two major developments have since changed the landscape, as anthropologist Manvir Singh, a professor at the University of California, describes in an article for The New Yorker.
New treatments and blood tests change the landscape
The first turning point came in 2021, when the U.S. Food and Drug Administration (FDA) began approving treatments based on monoclonal antibodies designed to slow the progression of Alzheimer’s disease.
All three treatments approved since then target amyloid, a protein that accumulates in the brain and forms the characteristic plaques associated with the disease. The two most recent treatments are currently available on the market.
The second major development concerns diagnosis. In May 2025, the FDA approved the first blood-based biomarker test for detecting abnormal findings associated with Alzheimer’s. Three additional approvals followed.
The new blood tests can approach the accuracy of positron emission tomography (PET) scans and cerebrospinal fluid analysis, offering a simpler way to identify biological changes linked to the disease.
“For the first time, we have simple blood tests that tell you whether you have Alzheimer’s,” Bill Gates said.
These advances have raised expectations that identifying the disease’s biological processes before symptoms appear, combined with treatments that can slow its progression, could eventually help prevent dementia.
Millions could show biological signs without developing Alzheimer’s
The scale of the issue is considerable. According to figures cited by Howard Feldman, a neurologist at the University of California, approximately one in four people over the age of 65 who show no apparent cognitive decline have amyloid accumulation in their brains.
On a global scale, this could mean hundreds of millions of people with biological indicators associated with Alzheimer’s.
However, the presence of amyloid does not mean that a person will inevitably develop the disease. Researchers estimate that only 5% to 10% of people with amyloid accumulation will develop Alzheimer’s within the following five years. Studies place their lifetime risk at approximately 25% to 33%.
This distinction lies at the heart of the debate over whether biological markers alone should be sufficient to define someone as having Alzheimer’s.
Scientists disagree over diagnosing the disease before symptoms
Supporters of early diagnosis argue that intervention should begin before cognitive symptoms emerge. By the time a person develops dementia, they say, extensive neurodegeneration has already occurred, and lost neural connections and memories cannot be restored. Identifying the disease earlier could therefore create an opportunity to intervene before irreversible damage becomes extensive.
Critics, however, caution that amyloid accumulation does not necessarily lead to dementia. They also point out that there is currently no evidence that administering anti-amyloid antibodies to people who have no cognitive impairment but test positive for biological markers can prevent the disease from developing.
The concern is that people could receive a diagnosis suggesting a future illness they may never experience, with potentially serious psychological consequences, without having access to a proven preventive treatment.
The disagreement also extends to the effectiveness of the new drugs, an issue that remains open to debate.
Biomarkers alone do not make someone a patient
Dr. Paraskevi Sakka, a neurologist and psychiatrist who heads the Athens Alzheimer’s Society, argues that diagnosis should combine clinical symptoms with biological markers.
People who test positive for biomarkers but show no symptoms should not automatically be considered patients, she says. Rather, they should be regarded as individuals at increased risk of developing Alzheimer’s.
Sakka says the term preclinical or presymptomatic Alzheimer’s should be reserved for people with an extremely high probability of developing dementia symptoms, such as those carrying autosomal dominant mutations.
She also emphasizes that a positive biomarker result does not necessarily mean someone will develop the disease during their lifetime. Instead, such tests can help identify people at risk and allow doctors to strongly recommend measures targeting modifiable risk factors.
New antibody treatments offer hope for selected patients
Sakka stresses that monoclonal anti-amyloid antibodies are intended for carefully selected patients who already have symptoms, specifically people with mild cognitive impairment or mild dementia.
The results are encouraging, she says, with the treatments slowing disease progression by up to 35% over an 18-month period.
She describes these drugs as marking a new era in Alzheimer’s treatment: one in which therapies target the underlying biological mechanisms of the disease rather than focusing solely on its symptoms.
The central question remains whether advances in early detection will eventually make it possible to intervene before cognitive decline begins — or whether expanding the definition of Alzheimer’s will lead to large numbers of people being labeled at risk without clear evidence that treatment can prevent the disease.
