雅思阅读 73: The Amyloid Hypothesis Under Siege（饱受质疑的淀粉样蛋白假说）

改编自 Ars Technica（2026年4月，Jonathan M. Gitlin）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://arstechnica.com/science/2026/04/whats-the-deal-with-alzheimers-disease-and-amyloid/

Reading Passage

A. The condition we now call Alzheimer's disease was first recorded in 1906, when the German neuropathologist Alois Alzheimer examined tissue from the brain of Auguste Deter, a woman who had died at just 55. Alzheimer observed two abnormal structures: plaques, which colleagues had already noted in other dementia patients, and tangled bundles of fibres inside nerve cells, which no one had described before. For the next eight decades these two hallmarks were essentially all that science knew about a cruel illness that strips away memory, skill and finally personality. Diagnosis was possible only after death, when a pathologist could inspect brain tissue for the plaques and tangles. That limitation made the disease peculiarly difficult to study: researchers could not watch it evolve in the living, only catalogue its ruins. The arrival of PET scanners, together with the discovery of measurable biomarkers in blood, eventually allowed physicians to detect the disease before a patient died, but the underlying cause remained stubbornly obscure. What exactly produced the plaques, and whether they were the engine of the illness or merely its by-product, became the central question that would shape a generation of research spending. For most of the twentieth century, Alzheimer's was widely regarded as a rare curiosity rather than the mass affliction it is now known to be; only as populations aged did the scale of the looming crisis become impossible to ignore.

B. The turning point came in 1984, when scientists identified a protein fragment called amyloid-β accumulating inside the plaques. No one was certain what amyloid-β did, but two coincidences made it suspicious. Researchers already found large quantities of the same protein in the brains of people with Down syndrome, who frequently develop dementia in later life. The gene that encodes the larger molecule from which amyloid-β is cut — amyloid precursor protein — sits on chromosome 21, and Down syndrome is caused by carrying an extra copy of that very chromosome. The following years strengthened the case: in 1987, patients with a rare inherited form of Alzheimer's were discovered to carry a mutation in their amyloid precursor protein gene. The logic seemed inescapable. If a single altered gene could trigger the disease, then excess amyloid-β must be the culprit. A pivotal 2006 paper in a leading journal appeared to clinch the argument, linking memory loss to a particular form of the protein outside neurons. From this grew the so-called amyloid cascade hypothesis, which held that stopping amyloid-β from clumping together, or removing the clumps once formed, would halt the disease itself.

C. A clear target invited experiments, and researchers naturally turned to mice — though mice never develop Alzheimer's on their own. By inserting a mutated copy of the human amyloid precursor protein gene into the rodent genome, however, scientists could engineer a version of the illness in which plaques reliably appeared. In 1999 a company called Elan Pharmaceuticals showed that a vaccine directed at part of amyloid-β cleared plaques from these engineered mice, whether it was given before plaques formed or after they had already accumulated. Because vaccines work by stimulating the body to make antibodies, the firm then demonstrated that anti-amyloid antibodies had the same plaque-clearing effect when injected directly. But there are many slips between mouse and human. When Elan tested its vaccine in patients with mild to moderate Alzheimer's, the trial of 360 volunteers had to be suspended after several developed serious inflammation of the brain. Other companies pursued antibodies targeting different points on the amyloid pathway; in animal models the plaques disappeared, yet the disease marched on. These disappointments did not, however, shake the conviction that the target itself was correct.

D. That conviction led to a succession of high-profile drug approvals that the evidence could barely support. In 2021 the US regulator approved aducanumab, an antibody from Biogen, even though it had failed not one but two large placebo-controlled trials in 2019; its manufacturers re-analysed the datasets and claimed a small benefit in one subgroup. A congressional inquiry later described the approval as riddled with irregularities, and the drug, priced at 65,000 dollars a year, was withdrawn from the market in 2024. Two later antibodies fared little better. Lecanemab, developed with Eisai and approved in 2023 at roughly half the price, was linked to the deaths of three patients from brain swelling and bleeding. Donanemab, from Eli Lilly, made headlines the same year when its trial data claimed to slow progression by about a third in early-stage disease — yet the cognitive gains were so slender that the side effects could feel like the only reliable signal that a patient was taking the drug. A 2026 review pooling 17 trials with more than 20,000 patients concluded that the antibodies clear amyloid from the brain but produce little measurable benefit to thinking or daily function.

E. Critics argue that the field has long been gripped by a kind of groupthink, dubbed the "Amyloid Mafia" by those on its margins. Scientists who controlled research grants were said to look unfavourably on proposals examining anything other than amyloid; one neuroinflammation specialist recalled that merely mentioning immunology could draw hostile reactions. The former head of Alzheimer's research at America's National Institute on Ageing described the hypothesis as gradually hardening into an "infallible belief system" that no one dared question. Meanwhile, rival explanations gathered evidence: inflammation driven by rogue immune cells in the brain; infections, from herpes virus to the mouth bacterium Porphyromonas gingivalis, which some researchers believe seed the plaques; and the composition of the gut microbiome. The trouble with each alternative is that far more people carry the implicated infections than ever develop Alzheimer's, suggesting the disease may require several insults to align. Compounding the doubts, several influential papers linking specific amyloid forms to memory loss have been retracted amid accusations of fabricated data, and at least one researcher has faced prosecution over the matter. Whether amyloid is the cause, a marker, or a red herring remains unresolved — but the decades-long conviction that it was simply the cause now looks less secure than anyone dared admit. The challenge for the next generation is to test these rival ideas without allowing any one of them to harden into the same kind of unchallengeable orthodoxy that held the field for so long.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The rise and genetic support for the amyloid theory ii. Why mice never develop Alzheimer's naturally iii. From promising animal models to a failed human vaccine iv. A wave of disputed drug approvals and their costs v. Rival explanations and the grip of groupthink vi. The role of PET scanners in diagnosis vii. The history of Alois Alzheimer's clinic

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. Why did amyloid-β look suspicious to researchers in the 1980s? A. It was found only in patients younger than 55. B. It appeared in Down syndrome brains and on chromosome 21. C. It permanently cured dementia in animal trials. D. It was absent from the plaques themselves.

6. What happened to Elan's vaccine when it was tested in human patients? A. It cured most participants within months. B. The trial was halted after some patients developed brain inflammation. C. It proved completely free of side effects. D. It was immediately approved without further testing.

7. What did the 2026 review of 17 trials conclude? A. The antibodies dramatically restored lost memory. B. The antibodies cleared amyloid but offered little cognitive benefit. C. The antibodies produced no side effects at all. D. The trials were too small to permit any judgement.

8. According to critics, what has discouraged research into alternative causes? A. There are simply no grant applications on other topics. B. Those controlling grants tended to reject non-amyloid proposals. C. Rival theories lack any supporting evidence. D. Regulators have banned inflammation research.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. Auguste Deter was 55 years old when she died.
10. The gene for amyloid precursor protein is located on chromosome 21.
11. Elan's vaccine trial enrolled only patients aged over 80.
12. Aducanumab successfully passed both of its large Phase III trials in 2019.
13. Several influential amyloid papers have been retracted over accusations of fabricated data.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

A 2026 review pooling 17 trials found that anti-amyloid antibodies remove (14) __________ from the brain, but deliver little measurable benefit to (15) __________ or daily function.

答案与解析

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