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categories: ["longevity", "foundations"]categories: ["longevity", "foundations"]tags: ["dementia", "neurodegeneration", "amyloid", "tau", "aging", "brain", "apoe"]tags: ["dementia", "neurodegeneration", "amyloid", "tau", "aging", "brain", "apoe"]summary: "The neurodegenerative disease responsible for most dementia, driven above all by age, and the disease that decides whether added years of life come with a working mind."summary: "The neurodegenerative disease responsible for most dementia, driven above all by age, and the disease that decides whether added years of life come with a working mind."updated: "2026-10-28"updated: "2026-10-29"humanEvidence: "Two anti-amyloid antibodies slowed cognitive decline by roughly a quarter to a third over 18 months in phase 3 trials; no treatment has stopped or reversed the disease in people."humanEvidence: "Two anti-amyloid antibodies slowed cognitive decline by roughly a quarter to a third over 18 months in phase 3 trials; no treatment has stopped or reversed the disease in people."issues: ["Tau-directed therapeutics and non-amyloid drug programmes are mentioned only in passing."]issues: ["Tau-directed therapeutics and non-amyloid drug programmes are mentioned only in passing."]------lines 17–38 → 17–383 unchanged lines not shown
"caption": "Neurodegenerative disease and constraint on healthspan", "caption": "Neurodegenerative disease and constraint on healthspan", "rows": [ "rows": [ { "label": "Kind of thing", "value": "Proteinopathy of the brain" }, { "label": "Kind of thing", "value": "Proteinopathy of the brain" }, { "label": "Share of dementia", "value": "60–70% of cases" }, { "label": "Share of dementia", "value": "60-70% of cases" }, { "label": "Living with dementia", "value": "~57 million worldwide (2021)" }, { "label": "Living with dementia", "value": "~57 million worldwide (2021)" }, { "label": "Principal risk factor", "value": "Age" }, { "label": "Principal risk factor", "value": "Age" }, { "label": "Strongest common risk gene", "value": "APOE ε4" }, { "label": "Strongest common risk gene", "value": "APOE ε4" }, { "label": "Defining pathology", "value": "Amyloid plaques, tau tangles" }, { "label": "Defining pathology", "value": "Amyloid plaques, tau tangles" }, { "label": "First described", "value": "1906" }, { "label": "First described", "value": "1906" }, { "label": "Disease-modifying drugs", "value": "Two approved (US, 2023–24)" } { "label": "Disease-modifying drugs", "value": "Two approved (US, 2023-24)" } ] ]}}`````` **Alzheimer's disease** is the neurodegenerative disease behind 60–70% of dementia: a progressive loss of memory, then language, judgement, and finally the capacity to live unassisted, marked in the brain by extracellular plaques of amyloid-β and tangles of tau protein inside neurons. Its overwhelming risk factor is age. For the arguments this wiki tracks it is the counterpart of [[cancer]]: cancer sets the ceiling on how long a body lasts, and Alzheimer's asks whether the mind lasts as long as the body does.**Alzheimer's disease** is the neurodegenerative disease behind 60-70% of dementia: a progressive loss of memory, then language, judgement, and finally the capacity to live unassisted, marked in the brain by extracellular plaques of amyloid-β and tangles of tau protein inside neurons. Its overwhelming risk factor is age. For the arguments this wiki tracks it is the counterpart of [[cancer]]: cancer sets the ceiling on how long a body lasts, and Alzheimer's asks whether the mind lasts as long as the body does. ```keyfacts```keyfacts[[ { "value": "~57M", "label": "People living with dementia worldwide", "note": "WHO estimate for 2021; Alzheimer's accounts for 60–70%" }, { "value": "~57M", "label": "People living with dementia worldwide", "note": "WHO estimate for 2021; Alzheimer's accounts for 60-70%" }, { "value": "27%", "label": "Slowing of decline with lecanemab over 18 months", "note": "0.45 points on the 18-point CDR-SB scale in CLARITY AD" }, { "value": "27%", "label": "Slowing of decline with lecanemab over 18 months", "note": "0.45 points on the 18-point CDR-SB scale in CLARITY AD" }, { "value": "45%", "label": "Of dementia linked to 14 modifiable risk factors", "note": "2024 Lancet Commission population-attributable estimate" } { "value": "45%", "label": "Of dementia linked to 14 modifiable risk factors", "note": "2024 Lancet Commission population-attributable estimate" }]]lines 40–49 → 40–491 unchanged line not shown
## An age-related disease## An age-related disease Dementia prevalence roughly doubles with every five years of age past 65, making it an old-age disease in the demographic sense cancer is. The World Health Organization estimates that 57 million people were living with dementia in 2021, with nearly 10 million new cases a year, and counts it the seventh leading cause of death worldwide; the Alzheimer's Association estimates 7.2 million Americans aged 65 and over have Alzheimer's dementia in 2025, with a projected near-doubling by 2060 absent better treatment or prevention.[^epi2025] The growth is driven by population aging; age-specific risk has actually declined in several high-income countries.Dementia prevalence roughly doubles with every five years of age past 65, making it an old-age disease in the demographic sense cancer is. The World Health Organization estimates that 57 million people were living with dementia in 2021, with nearly 10 million new cases a year, and counts it the seventh leading cause of death worldwide; the Alzheimer's Association estimates 7.2 million Americans aged 65 and over have Alzheimer's dementia in 2025, with a projected near-doubling by 2060 absent better treatment or prevention.[^epi2025] The growth is driven by population aging; age-specific risk has declined in several high-income countries. > [!key] Why this matters here> [!key] Why this matters here> Eliminating dementia would add little life expectancy, because its victims are old and die of something else soon after; what it would remove is a large share of late-life disability. That makes Alzheimer's the sharpest test of the distinction between lifespan and [[healthspan]], and the [[geroscience-hypothesis|geroscience]] reading, that it is a manifestation of brain aging rather than a disease that happens to strike the old, is one of its central claims. Any intervention that extends the body without protecting the brain extends the years in which this disease can arrive.> Eliminating dementia would add little life expectancy, because its victims are old and die of something else soon after; what it would remove is a large share of late-life disability. That makes Alzheimer's the sharpest test of the distinction between lifespan and [[healthspan]], and the [[geroscience-hypothesis|geroscience]] reading, that it is a manifestation of brain aging rather than a disease that happens to strike the old, is one of its central claims. An intervention that extends the life of the body without protecting the brain lengthens the period in which this disease can arrive. ## Plaques, tangles, and the amyloid hypothesis## Plaques, tangles, and the amyloid hypothesis lines 51–57 → 51–571 unchanged line not shown
Sleep and pathology may be connected through [[glymphatic-system|glymphatic]] clearance, the flow of cerebrospinal fluid along the spaces around blood vessels that mouse studies suggest carries amyloid-β and tau out of brain tissue. Its impairment is a hypothesised contributor to their accumulation, not an established one: how much bulk flow occurs is itself disputed, and the human evidence is indirect. In a 2026 *Science Advances* study, Liu and colleagues reported that ten-minute daily sessions of 40.68 MHz ultrashort-wave stimulation, a form of [[non-invasive-neuromodulation|non-invasive neuromodulation]], increased glymphatic flow in 5×FAD Alzheimer's model mice over a week, with less amyloid-β staining and better scores on two memory tests than untreated mice. The result is confined to mice.Sleep and pathology may be connected through [[glymphatic-system|glymphatic]] clearance, the flow of cerebrospinal fluid along the spaces around blood vessels that mouse studies suggest carries amyloid-β and tau out of brain tissue. Its impairment is a hypothesised contributor to their accumulation, not an established one: how much bulk flow occurs is itself disputed, and the human evidence is indirect. In a 2026 *Science Advances* study, Liu and colleagues reported that ten-minute daily sessions of 40.68 MHz ultrashort-wave stimulation, a form of [[non-invasive-neuromodulation|non-invasive neuromodulation]], increased glymphatic flow in 5×FAD Alzheimer's model mice over a week, with less amyloid-β staining and better scores on two memory tests than untreated mice. The result is confined to mice. The field's organizing idea, stated by Hardy and Higgins in 1992, is the amyloid cascade hypothesis: amyloid-β accumulation is the initiating event, and tau pathology, inflammation, synapse loss, and dementia follow downstream.[^hardy1992] The strongest evidence has always been genetic. The hypothesis's persistent embarrassment is anatomical: tangle burden tracks symptoms far better than plaque burden does, and a substantial minority of cognitively normal older people carry a plaque load that would support a diagnosis.The field's organizing idea, stated by Hardy and Higgins in 1992, is the amyloid cascade hypothesis: amyloid-β accumulation is the initiating event, and tau pathology, inflammation, synapse loss, and dementia follow downstream.[^hardy1992] The strongest evidence has always been genetic. The hypothesis's most persistent problem is anatomical: tangle burden tracks symptoms far better than plaque burden does, and a substantial minority of cognitively normal older people carry a plaque load that would support a diagnosis. ```timeline```timeline[[lines 78–88 → 78–8820 unchanged lines not shown
Between the cascade hypothesis and the first approval lie almost three decades in which every amyloid-directed drug failed, a record critics read as the hypothesis tested and found wanting, and defenders as trials run too late, on the wrong patients, with drugs that never engaged the target. Rival framings (tau-first, vascular, inflammatory, infectious) attracted attention in rough proportion to amyloid's setbacks. A 2022 investigation then found doctored images in a highly cited 2006 paper on the amyloid oligomer Aβ*56; Nature retracted it in June 2024.[^piller2022] The fraud touched one strand of oligomer work, not the genetics or the trials, but it sharpened the complaint that amyloid absorbed funding the alternatives never saw.Between the cascade hypothesis and the first approval lie almost three decades in which every amyloid-directed drug failed, a record critics read as the hypothesis tested and found wanting, and defenders as trials run too late, on the wrong patients, with drugs that never engaged the target. Rival framings (tau-first, vascular, inflammatory, infectious) attracted attention in rough proportion to amyloid's setbacks. A 2022 investigation then found doctored images in a highly cited 2006 paper on the amyloid oligomer Aβ*56; Nature retracted it in June 2024.[^piller2022] The fraud touched one strand of oligomer work, not the genetics or the trials, but it sharpened the complaint that amyloid absorbed funding the alternatives never saw. > [!debate] Is amyloid the cause?> [!debate] Is amyloid the cause?> Proponents point to the causal genetics and to the fact that the only drugs ever to slow the disease are the ones that clear plaques. Critics reply that the slowing is modest, that plaque removal is nearly complete while the clinical effect is not, and that tau tracks symptoms far better — consistent with amyloid being an upstream trigger, a partial cause, or a tombstone. The prevention trials now dosing amyloid-positive people before symptoms are the closest thing to a decisive experiment either side has proposed.> Proponents point to the causal genetics and to the fact that the only drugs ever to slow the disease are the ones that clear plaques. Critics reply that the slowing is modest, that plaque removal is nearly complete while the clinical effect is not, and that tau tracks symptoms far better. That pattern fits amyloid being an upstream trigger, a partial cause, or a tombstone. The prevention trials now dosing amyloid-positive people before symptoms are the closest thing to a decisive experiment either side has proposed. ## The antibody era## The antibody era Aducanumab's 2021 accelerated approval, granted on plaque clearance over its advisory committee's objection, ended as a cautionary tale: insurers balked, and Biogen discontinued the drug in January 2024. What replaced it is a genuine but modest result, twice replicated. In CLARITY AD, lecanemab slowed decline on the CDR-SB scale by 27% over 18 months (a difference of 0.45 points on an 18-point scale) and won traditional US approval in July 2023.[^vandyck2023] In TRAILBLAZER-ALZ 2, donanemab slowed decline by about 35% in the low-and-medium-tau population and was approved in July 2024, with dosing stopped once plaques clear.[^sims2023] Both drugs cause amyloid-related imaging abnormalities, or ARIA: brain swelling in 12.6% of lecanemab recipients and 24% of donanemab recipients — usually asymptomatic, though three deaths in the donanemab trial were attributed to it. Both require proven amyloid pathology, repeated MRI monitoring, and carry US list prices near $30,000 a year before the cost of scans and infusions.Aducanumab's 2021 accelerated approval, granted on plaque clearance over its advisory committee's objection, ended as a cautionary tale: insurers balked, and Biogen discontinued the drug in January 2024. What followed was a real but modest result, seen in two separate trials. In CLARITY AD, lecanemab slowed decline on the CDR-SB scale by 27% over 18 months (a difference of 0.45 points on an 18-point scale) and won traditional US approval in July 2023.[^vandyck2023] In TRAILBLAZER-ALZ 2, donanemab slowed decline by about 35% in the low-and-medium-tau population and was approved in July 2024, with dosing stopped once plaques clear.[^sims2023] Both drugs cause amyloid-related imaging abnormalities, or ARIA: brain swelling in 12.6% of lecanemab recipients and 24% of donanemab recipients. The swelling is usually asymptomatic, though three deaths in the donanemab trial were attributed to it. Both drugs require proven amyloid pathology and repeated MRI monitoring, and both carry US list prices near $30,000 a year before the cost of scans and infusions. > [!caution] Slowing is not stopping> [!caution] Slowing is not stopping> Treated patients in both trials continued to decline: the drugs bought back part of 18 months' worsening, not a plateau. The between-group differences sit below the one-point CDR-SB threshold many clinicians had used for a minimally important difference, and whether the benefit compounds, holds, or fades over five or ten years is unknown; the extension data so far come from sponsors, against external cohorts rather than placebo. Mainstream opinion spans "first disease-modifying success, build on it" to "marginal benefit at real risk and cost", and both positions cite the same trials.> Treated patients in both trials continued to decline: the drugs bought back part of 18 months' worsening, not a plateau. The between-group differences sit below the one-point CDR-SB threshold many clinicians had used for a minimally important difference, and whether the benefit compounds, holds, or fades over five or ten years is unknown; the extension data so far come from sponsors, against external cohorts rather than placebo. Mainstream opinion spans "first disease-modifying success, build on it" to "marginal benefit at real risk and cost", and both positions cite the same trials.lines 91–105 → 91–1072 unchanged lines not shown
## Diagnosis moves to blood## Diagnosis moves to blood For most of its history Alzheimer's could be confirmed only at autopsy, then by PET scans and lumbar punctures too costly and invasive to scale. In May 2025 the FDA cleared the first blood test for the underlying pathology, a plasma ratio of p-tau217 to amyloid-β 1-42 that tracks amyloid PET closely, for use in symptomatic adults aged 55 and over, explicitly not as a screening test.[^fda2025] Cheap blood biomarkers are quietly redefining the disease as a biological state that begins a decade or more before symptoms, the same preclinical framing the [[aging-biomarkers]] field wants for aging itself, and they raise the question that hangs over [[consumer-blood-testing]]: what a positive result is worth when intervention is unproven. Prevention trials dosing amyloid-positive, cognitively normal volunteers with the approved antibodies are underway, with results expected late this decade.For most of its history Alzheimer's could be confirmed only at autopsy, then by PET scans and lumbar punctures too costly and invasive to scale. In May 2025 the FDA cleared the first blood test for the underlying pathology, a plasma ratio of p-tau217 to amyloid-β 1-42 that tracks amyloid PET closely, for use in symptomatic adults aged 55 and over, explicitly not as a screening test.[^fda2025] Cheap blood biomarkers are redefining the disease as a biological state that begins a decade or more before symptoms, the same preclinical framing the [[aging-biomarkers]] field wants for aging itself, and they raise the question that hangs over [[consumer-blood-testing]]: what a positive result is worth when intervention is unproven. Prevention trials dosing amyloid-positive, cognitively normal volunteers with the approved antibodies are underway, with results expected late this decade. ## Prevention without a prescription## Prevention without a prescription The 2024 Lancet Commission attributes around 45% of dementia to 14 modifiable risk factors across the life course — from low education, hearing loss and hypertension to the two added in 2024, high midlife LDL cholesterol and untreated vision loss.[^livingston2024] The estimate is a theoretical ceiling built from observational associations, assuming each factor is causal and could be fully eliminated, and no trial has prevented Alzheimer's with any of it. It is still the only large claim on offer, and it points the same way as the falling age-specific incidence in some rich countries: dementia risk moves with education, blood pressure, [[exercise-and-aging|exercise]] and cardiovascular health before any drug enters the picture.The 2024 Lancet Commission attributes around 45% of dementia to 14 modifiable risk factors across the life course, from low education, hearing loss and hypertension to the two factors added in 2024: high midlife LDL cholesterol and untreated vision loss.[^livingston2024] The estimate is a theoretical ceiling built from observational associations, assuming each factor is causal and could be fully eliminated, and no trial has prevented Alzheimer's with any of it. It is still the only large claim on offer, and it points the same way as the falling age-specific incidence in some rich countries: dementia risk moves with education, blood pressure, [[exercise-and-aging|exercise]] and cardiovascular health before any drug enters the picture. ## What it means for longevity arguments## What it means for longevity arguments Alzheimer's is where [[compression-of-morbidity]] stops being an abstraction: added years spent with dementia are precisely the outcome that argument exists to rule out. Several interventions this wiki tracks have been tested against it, so far without clinical success: a [[senolytics]] pilot showed only tolerability, [[parabiosis-and-young-blood|young-plasma]] trials feasibility with debated efficacy, and a [[memory-prosthesis]] presumes circuitry the disease removes. The antibodies bound the arithmetic from the other side: the best therapy slows one disease of brain aging by about a third, at real risk, nowhere near the repeated, compounding rescue [[longevity-escape-velocity]] requires. For projects that treat the brain as the thing worth preserving, from [[brain-preservation]] outward, Alzheimer's is the demonstration that the substrate can fail first, slowly, while the body lasts. The open question is whether removing amyloid before symptoms prevents the disease rather than slightly delaying it; the prevention trials now running are the first able to answer.Alzheimer's is where [[compression-of-morbidity]] stops being an abstraction: added years spent with dementia are precisely the outcome that argument exists to rule out. Several interventions this wiki tracks have been tested against it, so far without clinical success: a [[senolytics]] pilot showed only tolerability, [[parabiosis-and-young-blood|young-plasma]] trials feasibility with debated efficacy, and a [[memory-prosthesis]] presumes circuitry the disease removes. The antibodies set a limit from the other side: the best therapy slows one disease of brain aging by about a third, at real risk, which is nowhere near the repeated, compounding rescue [[longevity-escape-velocity]] requires. For projects that treat the brain as the thing worth preserving, from [[brain-preservation]] outward, Alzheimer's shows that the substrate can fail first, slowly, while the body lasts. The open question is whether removing amyloid before symptoms prevents the disease rather than slightly delaying it; the prevention trials now running are the first able to answer. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
114 lines are the same in both revisions, and 55 of them are not shown. Neither revision here is necessarily the current article — read Alzheimer's disease for the text this wiki stands behind today.