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Alzheimer’s is a progressive disease that damages and kills neurons, but researchers have not established a single cause. Four leading explanations focus on amyloid plaques, tau tangles, brain inflammation and other factors that may interact; the supplied report describes evidence and limits, rather than a new discovery.
A Being Patient report describes four leading theories about what causes Alzheimer’s disease, while emphasizing that no single explanation is established. The theories focus on amyloid plaques, tau tangles, inflammation and other contributors to brain-cell damage, a question that matters to the millions of people affected by the progressive disease and to the development of treatments.
Alzheimer’s damages and eventually kills neurons and their connections, disrupting how the brain carries information. Damage often begins in the hippocampus, which is important for forming new memories, and can later affect language, judgment, behavior and coordination. The report cites the Alzheimer’s Association’s 2026 Facts and Figures report, which estimates 7.4 million Americans aged 65 and older are living with Alzheimer’s dementia.
The best-known explanations center on two features first described by Alois Alzheimer in 1906: amyloid plaques, clusters of protein fragments between neurons, and tau tangles, abnormal fibers inside them. The amyloid hypothesis proposes that beta-amyloid accumulates and may trigger a chain of damage; the tau theory focuses on tau losing its normal role in supporting a neuron’s internal structure. The supplied source text ends partway through its discussion of tau and does not provide the names or detail of the other two theories.
The report says amyloid research has shaped drug development, with mixed outcomes. Aduhelm (aducanumab), an earlier FDA-approved antibody, was discontinued by its maker in 2024 after evidence of clinical benefit was unconvincing. Leqembi (lecanemab) and Kisunla (donanemab) are approved for people in early stages of Alzheimer’s; the report says trials found they modestly slowed cognitive decline, not cured the disease. It also notes risks of brain swelling and bleeding that require monitoring.
Why Alzheimer’s Cause Matters
Understanding what drives Alzheimer’s could help researchers identify which biological changes to target and when. The report says amyloid accumulation may begin years or decades before symptoms, making early detection and treatment a major focus. Amyloid PET scans and spinal-fluid tests can detect related pathology, and the FDA cleared a blood test in May 2025 to aid identification of amyloid pathology linked to Alzheimer’s.
At the same time, the treatment record cautions against treating one theory as a complete account. Amyloid-targeting medicines can slow decline in some early-stage patients, according to the report, but they do not stop or reverse the disease and carry risks. Better understanding may shape future research, but the report does not establish that any one mechanism alone causes Alzheimer’s.
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From Plaques to Treatment Research
In November 1906, German psychiatrist Alois Alzheimer described findings in the brain of former patient Auguste Deter, who died at 55 after worsening memory loss, confusion and paranoia. The plaques and twisted fibers he observed later became known as amyloid plaques and tau tangles. They remain defining features used to study the disease, but recognizing them has not resolved what begins the process.
For more than three decades, the amyloid hypothesis has been a dominant framework, according to Being Patient. In that account, beta-amyloid fragments normally form and are cleared from the brain, but in Alzheimer’s they accumulate. The source notes that the theory is contested: some researchers have suggested amyloid may also have a protective function and point to trials in which blocking its production worsened clinical performance.
“Both γ-secretase and β-secretase inhibitors, which strongly inhibit amyloid-beta production, worsen cognitive and clinical performance in early and late stages of Alzheimer’s disease.”
— Bruno Imbimbo, a researcher at Chiesi Farmaceutici, as quoted by Being Patient
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What Scientists Still Disagree On
The initiating cause remains unknown. The report presents several theories as partial explanations, not a settled account of why neurons begin to fail. It also describes disagreement over whether amyloid is harmful, protective in some circumstances, or part of a broader sequence involving other changes.
The supplied source material does not include the full explanations of all four theories: its text cuts off during the tau section. It therefore does not support a detailed account of the remaining theories or a claim that the four mechanisms are equally established. Nor does it specify which patients benefit most from anti-amyloid treatment beyond the early-stage group described, or provide individual treatment guidance.
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Research Beyond Amyloid Plaques
Researchers continue to test how amyloid, tau and other biological processes relate to neuronal damage, symptoms and one another. The practical next steps described in the report include ongoing use and evaluation of early-stage anti-amyloid treatments, which require monitoring for brain swelling and bleeding, and the use of tests that identify amyloid pathology.
The supplied material does not name a next clinical milestone or give a timeline for resolving the competing explanations. Further studies will be needed to clarify which processes drive disease, how early they can be identified and whether targeting more than one process can improve outcomes.
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Key Questions
Do scientists know what causes Alzheimer’s?
No single cause is established. The report describes several leading theories that may explain parts of the disease process.
What are amyloid plaques and tau tangles?
Amyloid plaques are accumulations of beta-amyloid protein fragments between neurons. Tau tangles are abnormal fibers inside neurons. Both are characteristic findings in Alzheimer’s, but their presence alone does not settle what initiates the disease.
Do amyloid-targeting drugs cure Alzheimer’s?
No. The report says Leqembi and Kisunla modestly slowed cognitive decline in clinical trials among people in early stages of the disease. It describes them as not being cures and notes risks requiring regular monitoring.
The report says amyloid pathology can be detected using PET scans and spinal-fluid testing. It also says the FDA cleared a blood test in May 2025 to aid in identifying amyloid pathology linked to Alzheimer’s.
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