# Amyloid-beta as the Primary Upstream Cause of Alzheimer's Disease: research update

Dated 5 October 2026. Local prepublication addendum; archived grade unchanged.

Genetics, biomarker ordering and treatment trials support an upstream amyloid contribution in defined settings. Benefit after plaque removal varies across trials, and a universal amyloid-to-tau-to-neurodegeneration chain remains a separate question.

## Research timeline

Electronic year is used where recorded; issue year is retained in each source card. The chronology is selected, not exhaustive, and does not establish priority or causation.

| Year | Primary study | Design and finding | Inference limit |
|---|---|---|---|
| 1991 | [Segregation of a missense mutation in the amyloid precursor protein gene with familial Alzheimer's disease.](https://pubmed.ncbi.nlm.nih.gov/1671712/) | Familial segregation. APP missense variation segregated with familial Alzheimer disease. | A specific inherited route does not establish the initiating cause of all sporadic disease. |
| 2005 | [APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy.](https://pubmed.ncbi.nlm.nih.gov/16369530/) | Familial copy-number study. APP duplication was identified in families with early-onset disease and cerebral amyloid angiopathy. | The duplicated locus and inherited exposure differ from ordinary sporadic disease. |
| 2007 | [Reducing endogenous tau ameliorates amyloid beta-induced deficits in an Alzheimer's disease mouse model.](https://pubmed.ncbi.nlm.nih.gov/17478722/) | Mouse tau reduction. Reducing tau prevented deficits despite persistently high amyloid. | A model-specific downstream dependency does not establish the human mediation chain. |
| 2012 | [Clinical and biomarker changes in dominantly inherited Alzheimer's disease.](https://pubmed.ncbi.nlm.nih.gov/22784036/) | DIAN baseline biomarker study. Biomarker abnormalities were ordered relative to expected inherited-disease onset. | The authors called for longitudinal confirmation; chronology is not a causal perturbation. |
| 2012 | [A mutation in APP protects against Alzheimer's disease and age-related cognitive decline.](https://pubmed.ncbi.nlm.nih.gov/22801501/) | Human genetics plus cell assay. APP A673T was associated with protection and reduced amyloidogenic peptide formation in vitro. | Rare lifelong genetic exposure is not equivalent to late-life plaque removal. |
| 2019 | [Resistance to autosomal dominant Alzheimer's disease in an APOE3 Christchurch homozygote: a case report.](https://pubmed.ncbi.nlm.nih.gov/31686034/) | Single protective-genotype case. An APOE3 Christchurch homozygote had delayed impairment despite extensive amyloid. | A single case bounds simple sufficiency but cannot estimate prevalence. |
| 2022 | [Lecanemab in Early Alzheimer's Disease.](https://pubmed.ncbi.nlm.nih.gov/36449413/) | Clarity AD randomized trial. Lecanemab modestly slowed decline over 18 months, with adverse events. | Treatment contribution does not establish disease initiation or complete tau mediation. |
| 2023 | [Donanemab in Early Symptomatic Alzheimer Disease: The TRAILBLAZER-ALZ 2 Randomized Clinical Trial.](https://pubmed.ncbi.nlm.nih.gov/37459141/) | TRAILBLAZER-ALZ 2 randomized trial. Donanemab slowed progression in the prespecified symptomatic trial populations. | Selected amyloid/tau-positive participants and treatment harms bound generalization. |
| 2023 | [Two Phase 3 Trials of Gantenerumab in Early Alzheimer's Disease.](https://pubmed.ncbi.nlm.nih.gov/37966285/) | GRADUATE I and II randomized trials. Gantenerumab reduced plaques without significant benefit on either trial’s primary clinical endpoint. | Incomplete clearance and exposure duration limit a universal negative interpretation; two trials are one report. |
| 2024 | [Biomarker Changes during 20 Years Preceding Alzheimer's Disease.](https://pubmed.ncbi.nlm.nih.gov/38381674/) | Sporadic nested case-control follow-up. Amyloid-related biomarkers diverged before other markers and cognitive decline. | Observed ordering does not isolate a necessary cause. |
| 2025 | [Safety and efficacy of long-term gantenerumab treatment in dominantly inherited Alzheimer's disease: an open-label extension of the phase 2/3 multicentre, randomised, double-blind, placebo-controlled platform DIAN-TU trial.](https://pubmed.ncbi.nlm.nih.gov/40120616/) | DIAN-TU open-label extension. Long exposure suggested possible delay, while short or partial removal lacked significant clinical effects. | External controls and extension selection prevent treating this as a fresh randomized prevention result. |

## Research gaps

### G1: Does early amyloid removal prevent sporadic clinical onset?

Evidence anchors: [P36449413](https://pubmed.ncbi.nlm.nih.gov/36449413/), [P37459141](https://pubmed.ncbi.nlm.nih.gov/37459141/), [P38381674](https://pubmed.ncbi.nlm.nih.gov/38381674/), [P40120616](https://pubmed.ncbi.nlm.nih.gov/40120616/).

Competing explanation: Late symptomatic benefit may reflect contribution after initiation, while tau or other injury becomes self-sustaining.

Discriminating test and controls: Long-duration prevention randomization in biomarker-defined presymptomatic groups; prespecify clinical onset, clearance, tau trajectory and adverse events.

### G2: Does tau change mediate clinical benefit?

Evidence anchors: [P17478722](https://pubmed.ncbi.nlm.nih.gov/17478722/), [P37459141](https://pubmed.ncbi.nlm.nih.gov/37459141/), [P37966285](https://pubmed.ncbi.nlm.nih.gov/37966285/).

Competing explanation: Amyloid and tau biomarkers can move together without tau carrying the treatment effect.

Discriminating test and controls: Repeated tau PET and neurodegeneration measures within randomization; specify mediator timing, missingness and sensitivity to mediator–outcome confounding.

### G3: Which clearance, species and exposure matter?

Evidence anchors: [P36449413](https://pubmed.ncbi.nlm.nih.gov/36449413/), [P37459141](https://pubmed.ncbi.nlm.nih.gov/37459141/), [P37966285](https://pubmed.ncbi.nlm.nih.gov/37966285/), [P40120616](https://pubmed.ncbi.nlm.nih.gov/40120616/).

Competing explanation: Differences may arise from drug kinetics, target species, dose, disease stage or incomplete clearance.

Discriminating test and controls: Harmonized analyses and prospectively matched trials with target engagement, baseline tau and equivalent outcome schedules; avoid cross-trial causal attribution.

### G4: Where does amyloid fail to be sufficient?

Evidence anchors: [P1671712](https://pubmed.ncbi.nlm.nih.gov/1671712/), [P16369530](https://pubmed.ncbi.nlm.nih.gov/16369530/), [P31686034](https://pubmed.ncbi.nlm.nih.gov/31686034/).

Competing explanation: Protective host factors may block downstream tau pathology despite high amyloid.

Discriminating test and controls: Genotype-stratified longitudinal cohorts and mechanistic follow-up with independent protective cases; retain disease subtype boundaries.

## Methods and access

Case-specific Consensus records assisted gap discovery, chronology and targeted paper questions. Shared template wording about an amyloid-specific Deep follow-up is not evidence of a Deep run for this topic; the dated source records establish the actual use and access limits. Primary identifiers, selected abstract passages, correction notices and available primary-body passages were cross-checked. Generated absence cells, duplicate milestones and unsupported access claims were rejected.

This focused addendum does not establish 50–70 complete primary Methods/Results examinations per review. Baseline reading receipts and scores retain their original scope.

Checked timeline sources: 11; selected full-text checks: 1; abstract-excerpt checks: 10; metadata-only historical anchors: 0. Complete papers examined in this update: 0.

Historical scorecards declare schema 5.4. This enrichment uses HSEF v5.3 causal distinctions without retrospectively relabelling or rescoring those files.

Targeted paper-check scope: Results P25/P28: both trial-specific primary CDR-SB tests were nonsignificant; only a minority attained amyloid-negative status. Pooled/exploratory results are not replacements for the primary tests.

Editorial correction/limit: The first Pro timeline duplicated four reports into ten entries. It was replaced after a Deep follow-up and primary-record checks. Retracted Lesné 2006 is excluded from positive evidence.