Why 1 in 2 Seniors Get Alzheimer's (And How to Be the Exception)

Accumulation of beta-amyloid in the brain is not the cause of Alzheimer's disease.

"That is absolutely not the cause of Alzheimer's disease. I say that in the book, provide the data, explain how the whole amyloid hypothesis was flawed." (said at 0:19:22)

The speaker's categorical assertion that beta-amyloid accumulation is 'absolutely not the cause of Alzheimer's disease' and that the amyloid hypothesis is entirely flawed contradicts extensive genetic, biochemical, and clinical trial evidence. Dominant mutations causing early-onset familial Alzheimer's disease (in APP, PSEN1, and PSEN2) and gene dosage effects in Down syndrome all directly alter amyloid-beta (Aβ) production or processing, establishing that Aβ dyshomeostasis is a key initiating causative factor in AD pathogenesis. While the original linear 'amyloid cascade hypothesis' has evolved—recognizing that Alzheimer's is multifactorial and that downstream tau neurofibrillary tangles, neuroinflammation, and synaptic loss drive cognitive decline—Aβ is well established as a critical upstream driver, and recently approved monoclonal antibodies that clear Aβ (e.g., lecanemab, donanemab) demonstrate statistically significant slowing of clinical disease progression.

• contradicts: The amyloid hypothesis of Alzheimer's disease at 25 years. (EMBO molecular medicine 2016) · cited 6256x in the literature

  "Despite continuing debate about the amyloid β-protein (or Aβ) hypothesis, new lines of evidence from laboratories and clinics worldwide support the concept that an imbalance between production and clearance of Aβ42 and related Aβ peptides is a very early, often initiating factor in Alzheimer's disease (AD). Confirmation that presenilin is the catalytic site of γ-secretase has provided a linchpin: all dominant mutations causing early-onset AD occur either in the substrate (amyloid precursor protein, APP) or the protease (presenilin) of the reaction that generates Aβ." (abstract, results)

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• context: Anti-Amyloid Therapies for Alzheimer's Disease and the Amyloid Cascade Hypothesis. (International journal of molecular sciences 2023) · cited 93x in the literature

  "Indeed, even Aducanumab and Lecanemab, the two antibodies recently approved by the FDA for AD therapy, as well as Donanemab showed limited efficacy on cognitive parameters in phase III clinical trials, despite their capability of markedly lowering Aβ brain load. Furthermore, preclinical evidence demonstrates that Aβ possesses several physiological functions, including memory formation, suggesting that AD may in part be due to a loss of function of this peptide. Finally, it is generally accepted that AD could be the result of many molecular dysfunctions" (abstract, results, passage verified)

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Higher blood levels of phosphorylated tau 217 (p-tau217) serve as a biomarker indicating the loss of synapses in the brain.

"the higher the level of this p-tau217 blood test, that is an indication of loss of synapses. It is therefore—and what is causing loss of the synapses? Activation of the microglial cells." (said at 0:28:10)

The speaker claims that higher blood levels of p-tau217 indicate a loss of synapses in the brain. In Alzheimer's disease biomarker frameworks and extensive clinical literature, phosphorylated tau (including p-tau217) specifically reflects amyloid-beta plaque pathology and neurofibrillary tau tangle pathology (specifically tau phosphorylation/secretion in response to amyloidosis), not synaptic loss directly. Synaptic loss is measured by distinct fluid biomarkers (such as neurogranin, NPTX2, synaptotagmin, or SV2A PET imaging) or markers of neurodegeneration (such as neurofilament light chain [NfL]), whereas p-tau217 specifically indicates amyloid and tau pathology.

• contradicts: Predicting continuous amyloid PET levels with CSF and plasma brain-derived p-tau217. (Alzheimer's & dementia : the journal of the Alzheimer's Association 2026)

  "Conventional phosphorylated tau (p-tau)217 reliably identifies amyloid positron emission tomography (PET) positivity, but its ability to capture the full Aβ continuum is limited." (abstract, background)

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• contradicts: Head-to-head comparison of plasma biomarker assays across platforms for amyloid pathology … (Science bulletin 2026)

  "With the advancement of anti-amyloid treatments for Alzheimer disease, accurate assays for amyloid-β (Aβ) pathology are essential. Plasma phosphorylated tau 217 (p-tau217) is a blood-based biomarker" (abstract, background)

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