While physicians and scientists have long known Alzheimer’s disease involves the buildup of toxic protein fragments in the brain, they have struggled to understand how these harmful fragments are produced.

Now, in a study published in Science Translational Medicine, Northwestern University scientists have pinpointed when and where toxic proteins accumulate within the brains of Alzheimer’s patients — and discovered a decades-old Food and Drug Administration (FDA)-approved drug that can stop the accumulation process before it even begins.

By studying animal models, human neurons and brain tissue from high-risk patients, the team discovered a particularly toxic protein fragment, called amyloid-beta 42, accumulates inside neurons’ synaptic vesicles — the tiny packets that neurons use to send signals. But, when the scientists administered levetiracetam (an inexpensive, decades‑old anti‑seizure drug) to the animals and human neurons, the drug prevented neurons from forming amyloid-beta 42.