Research
Alzheimer's: What do we know about the causes?
Article no. 7 · March 3, 2026 · Updated September 20, 2026 ·
Alzheimer's disease is the most common cause of dementia, accounting for approximately 60–70% of all cases. The disease develops slowly over many years, affecting memory, language, orientation, and eventually overall cognitive ability. Despite enormous research efforts, there is still no complete explanation for why the disease occurs. However, we have several well-founded theories – and increasingly, evidence suggests that Alzheimer's does not have a single cause but is the result of several interacting processes. This article attempts to provide an overview of the most important hypotheses.
##1. The Amyloid Hypothesis – Plaque as the Initiator##
The most well-known theory is the amyloid hypothesis.
In Alzheimer's, the protein amyloid-beta accumulates in the brain, forming plaques between nerve cells. These plaques are believed to: • disrupt communication between nerve cells • trigger inflammation • contribute to cell death in the long term
Support for the hypothesis: • People with Down syndrome (extra chromosome 21) often develop Alzheimer's – the gene for amyloid is located on chromosome 21. • Mutations in the APP, PSEN1, and PSEN2 genes can cause early-onset Alzheimer's.
Problems with the hypothesis: • Many elderly individuals have amyloid in their brains without symptoms. • Drugs that reduce amyloid have so far shown only moderate clinical effect.
Today, many researchers view amyloid more as an initial signal than the entire explanation.
⸻
##2. The Tau Hypothesis – The Collapse of the Nerve Cell##