TL;DR
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A Being Patient report outlines four leading theories for Alzheimer’s disease: amyloid buildup, tau tangles, inflammation and vascular damage. Each may explain part of how neurons are damaged, but researchers have not established one complete cause; the theories continue to shape research and treatment.
Alzheimer’s progressively damages neurons and the connections through which brain cells communicate. The loss of cells and connections can affect memory, language, judgment and behavior. The report says memory problems often emerge early because the disease commonly affects the hippocampus, which helps form new memories.
The amyloid hypothesis proposes that beta-amyloid fragments accumulate outside neurons and form plaques, potentially disrupting communication and setting off further damage. The tau theory focuses on a protein that normally helps stabilize structures inside neurons. When tau changes and clumps into tangles, those structures can fail and cells may be harmed. The report presents these as theories, not as a settled account of the disease.
Two other lines of research focus on inflammation and vascular damage. Inflammation involving the brain’s immune cells may contribute to injury, while impaired blood flow or damage to small blood vessels may deprive brain tissue of oxygen and nutrients. These processes can overlap with amyloid and tau, and the report does not establish that any one of them acts alone or is the primary cause.
How the Theories Shape Treatment
The theories matter because they influence which biological processes researchers try to measure and treat. Amyloid has guided much drug development: the report says the FDA has approved Leqembi (lecanemab) and Kisunla (donanemab) for people in early stages of Alzheimer’s. In clinical trials, the drugs modestly slowed cognitive decline; they are not cures, and treatment carries risks including brain swelling and bleeding that require monitoring.
The earlier anti-amyloid drug Aduhelm (aducanumab) cleared plaques, but the report says evidence of clinical benefit was unconvincing and its maker discontinued it in 2024. These mixed outcomes illustrate why identifying a biological marker or removing plaques does not, by itself, settle what causes the full range of disease symptoms. Research into tau, inflammation and vascular health may point to other targets or combinations of approaches.
For readers and families, the distinction is relevant to understanding what a test or treatment can show. Amyloid findings can support identification of Alzheimer’s-related pathology, but they do not amount to a complete explanation of why a particular person develops the disease or how it will progress.
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From Plaques to Multiple Pathways
In 1906, psychiatrist Alois Alzheimer described plaques and twisted fiber bundles in the brain of former patient Auguste Deter. Those findings are now known as amyloid plaques and tau tangles, and remain hallmarks of Alzheimer’s. Their presence helped establish the disease’s defining biology, but finding them did not answer what starts the chain of events that damages neurons.
For more than three decades, the amyloid hypothesis has been a dominant framework in Alzheimer’s research. The report says amyloid accumulation may begin years or decades before symptoms and may contribute to later changes, including tau tangles. Amyloid has also become part of diagnosis: it can be assessed using PET scans and spinal-fluid testing. In May 2025, the FDA cleared the first blood test to aid in identifying amyloid pathology linked to Alzheimer’s, according to the report.
The scale of the issue is reflected in the report’s citation of the Alzheimer’s Association’s 2026 Facts and Figures: an estimated 7.4 million Americans aged 65 and older were living with Alzheimer’s dementia. That estimate describes the U.S. population in that age group, not the number of people worldwide or the number of new cases.
““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
What Researchers Have Not Settled
No single cause has been established. The report describes multiple theories, and the biological processes may interact. It remains unclear which changes initiate Alzheimer’s in different people, how much each pathway contributes, and whether the same sequence applies across patients.
The report also raises debate over amyloid’s role: some researchers have suggested beta-amyloid may have protective functions, while certain drugs that block its production have been associated with worse cognitive and clinical performance, according to Imbimbo. That statement does not resolve the broader evidence on amyloid-targeting treatments. The reported trial benefits from newer antibodies are modest, and treatment risks and monitoring requirements remain relevant.
Risk factors, individual disease progression and the relationship between brain pathology and symptoms also remain areas of study. The article does not provide evidence that any one of the four theories can predict who will develop Alzheimer’s or explain every case.
Research Moves Beyond One Target
Researchers continue testing treatments that target amyloid and studying tau, inflammation and blood-vessel health. The next evidence to watch includes results from clinical trials, whether treatments can produce meaningful benefits for patients, and how safely they can be used over time. The report does not identify a specific forthcoming trial result or date.
Diagnostic research is also developing, with amyloid blood testing adding to PET scans and spinal-fluid tests as a way to help identify Alzheimer’s-related pathology. Further work will be needed to establish how such tests should be used alongside symptoms and other clinical information. For now, the four theories offer research directions—not a final answer to what causes Alzheimer’s.
Key Questions
What causes Alzheimer’s disease?
Researchers have not established one complete cause. Leading theories focus on amyloid plaques, tau tangles, inflammation and vascular damage, which may overlap in damaging brain cells.
Are amyloid plaques the proven cause of Alzheimer’s?
No. Amyloid plaques are a hallmark of the disease and a major research target, but the amyloid hypothesis remains debated. The report describes mixed treatment results and continuing questions about amyloid’s role.
What is the difference between amyloid plaques and tau tangles?
Amyloid plaques are deposits that collect outside neurons. Tau tangles form inside neurons when tau, a protein involved in stabilizing cell structures, changes and clumps.
Do Alzheimer’s drugs remove the disease?
No. The report says Leqembi and Kisunla modestly slowed cognitive decline in clinical trials among people in early stages; they are not cures and have risks that require monitoring.
Can a blood test diagnose Alzheimer’s?
The report says the FDA cleared a blood test in May 2025 to aid in identifying amyloid pathology linked to Alzheimer’s. It is a tool for detecting a biological marker, not a complete explanation of symptoms or disease progression.
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