U.S. researchers cut Alzheimer’s risk by half in first-ever prevention trial

Story: 2026 C.E.  |  Last updated: April 20, 2026

For the first time, scientists have shown that removing amyloid plaques from the brain before any symptoms appear can cut the risk of developing Alzheimer’s disease by roughly 50%. The Alzheimer’s prevention trial, run by researchers at Washington University School of Medicine in St. Louis, enrolled people who carry rare genetic mutations that make the disease nearly inevitable — and found that early, aggressive treatment can genuinely change the disease’s course. The results were published in The Lancet Neurology.

At a glance

• Alzheimer’s prevention trial: The Dominantly Inherited Alzheimer Network Trials Unit (DIAN-TU), launched in 2012, ran an open-label extension enrolling 73 participants who received the antibody drug gantenerumab at doses up to 1,500 mg every two weeks.
• Amyloid clearance: Participants who achieved near-normal amyloid levels — or who began treatment many years before their expected symptom onset — showed roughly a 50% reduction in risk of progressing to dementia compared to untreated controls.
• Confirmatory study: Although manufacturer Roche discontinued gantenerumab in 2022, the findings have launched a new follow-on trial — the DIAN-TU Amyloid Removal Trial — now running at 18 sites across Australia, Canada, France, Ireland, Puerto Rico, Spain, the U.K., and the U.S.

How the trial worked

The study focused on people with dominantly inherited Alzheimer’s disease (DIAD), a rare genetic form caused by mutations in the PSEN1, PSEN2, or APP genes. It accounts for fewer than 1% of all Alzheimer’s cases but leads to dementia with near-certainty, typically striking in a person’s 40s or 50s.

That grim predictability is also what makes this population so scientifically valuable. Researchers can estimate within a few years when symptoms will appear, allowing them to test interventions at precise points in the disease’s timeline.

The DIAN-TU study initially tested gantenerumab and another antibody, solanezumab, against a placebo. The early phase showed no significant cognitive benefit — largely because participants without symptoms had no measurable decline to reverse. Researchers then escalated to an open-label extension using much higher doses. That extension ran for up to three years before Roche discontinued the drug, not for safety reasons, but because gantenerumab failed to meet endpoints in larger trials targeting the more common late-onset form of Alzheimer’s.

The Washington University team pressed on, comparing outcomes from the extension against external controls drawn from an observational study of untreated mutation carriers. The 50% risk reduction signal emerged specifically among those who cleared amyloid most completely and those who began treatment earliest.

Why this result is different

Anti-amyloid drugs including lecanemab and donanemab, both of which received F.D.A. approval in recent years, showed they could slow cognitive decline in people who already had early symptoms. That was real progress.

But none had demonstrated what this trial now suggests: that clearing amyloid before symptoms emerge could prevent the disease from appearing at all.

That distinction reshapes how prevention trials can be designed. Amyloid begins accumulating in the brain roughly two decades before symptoms appear. The DIAN-TU team used DIAD’s predictability to intervene at the earliest possible biological window — and found evidence that the window matters enormously. Reaching near-normal amyloid levels before the brain has begun to show functional decline may be the threshold that determines whether the disease takes hold.

The DIAN-TU Amyloid Removal Trial now underway is designed to answer the follow-on questions: how much amyloid must be removed, how early, and for how long to produce durable protection in a randomized, controlled setting.

What the limitations tell us

The researchers are direct about what this trial cannot yet prove. The open-label design and the reliance on external rather than randomized controls introduce real statistical uncertainty. Statistically significant clinical benefit did not appear across the full participant group — the 50% risk reduction signal emerged within two specific subgroups.

The authors describe the findings as clinically meaningful but preliminary, and they say confirmation in longer, more rigorous trials is essential before results can guide broader treatment decisions. Gantenerumab itself is no longer available, and the more than 55 million people worldwide currently living with dementia will not benefit directly from these findings. That is the honest part of an otherwise encouraging picture.

Part of a longer arc

Alzheimer’s has long been the most stubborn exception to a documented global trend of improving health outcomes. For decades, research produced biological insight but no meaningful power to alter the disease’s course.

This trial changes that picture — not by solving Alzheimer’s, but by establishing that the disease may be interruptible before it begins. That kind of foundational result is how medical progress actually works: imperfect, preliminary, but pointing clearly in a direction.

The work coming out of Washington University, and from the international network of researchers contributing to DIAN-TU, fits the same pattern visible in other long-running scientific efforts — sustained investment, measured in decades, eventually moving numbers that once seemed impossible to shift. Both a specific biological target and a specific intervention window are now on the table. A decade ago, neither was.

Read more

For more on this story, see: Alzheimer’s Weekly

For more from Good News for Humankind, see:

• Alzheimer’s risk cut in half by drug in landmark prevention trial
• Ghana protects a stretch of the Atlantic at Cape Three Points
• The Good News for Humankind archive on global health

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