Rare brain study sheds light on Alzheimer's drug failures

Rare brain autopsy has provided fresh insight into why some Alzheimer's drugs may not deliver the benefits researchers had hoped for, suggesting one treatment may have failed because it did not reach every part of the brain.

The findings come from a case study published in JAMA, in which researchers examined the brain of a man who had received 30 doses of the now-discontinued Alzheimer's drug aducanumab over four-and-a-half years. They found that while some brain regions had been cleared of amyloid-beta plaques and tau tangles, other areas still contained significant amounts of both, potentially limiting the drug's effectiveness.

Brain showed uneven plaque removal

Researchers compared the patient's brain with those of people with dementia who had not received aducanumab. They found lower levels of amyloid plaques in the outer layers of the brain, while deeper cortical regions continued to show heavy plaque buildup.

The uneven distribution suggests the antibody treatment may not have penetrated every part of the brain effectively.

Scientists also observed that brain regions with lower amyloid levels contained fewer tau tangles and showed slower brain tissue shrinkage, supporting the idea that reducing amyloid may help limit the accumulation of tau, another protein linked to Alzheimer's disease.

Researchers see valuable clues despite limitations

The research team described the case as a rare opportunity to compare treated and untreated brain regions within the same patient.

They said the findings provide some of the strongest human evidence so far that removing amyloid plaques could help slow the spread of tau pathology and reduce neurodegeneration in certain areas of the brain.

However, researchers stressed that the study involved only one patient, meaning the results cannot be broadly applied to everyone with Alzheimer's disease.

Debate over Alzheimer's treatment continues

Aducanumab received accelerated approval from the U.S. Food and Drug Administration in 2021 despite mixed clinical results. Its manufacturer, Biogen, discontinued the drug in 2024 as it shifted its Alzheimer's strategy.

The new findings add to the ongoing debate over whether targeting amyloid plaques alone is enough to treat Alzheimer's. While some researchers believe early plaque removal could slow disease progression, others argue that amyloid and tau may be consequences rather than primary causes of dementia.

A review published earlier this year examining 17 clinical trials involving more than 20,000 participants found that anti-amyloid drugs produced no clinically meaningful improvement in people with mild cognitive impairment or early Alzheimer's disease.

Researchers say additional studies and ongoing clinical trials will be needed to determine whether earlier treatment or different approaches can produce better outcomes for patients.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition