Most people know Alzheimer's seems to run in families, and that some people face far higher odds than others. The gene most tied to that risk is called APOE4. What has long puzzled scientists is why a share of carriers never develop the disease.
Researchers at Columbia University Irving Medical Center say they have found a molecular answer. A rare mutation in a gene called FN1 appears to shield APOE4 carriers by stopping a protein from piling up around blood vessels in the brain.
The study appeared in Nature Aging on September 11, 2026. It builds on 2024 work from the same team that linked the rare FN1 variant to a 71 percent lower Alzheimer's risk in APOE4 carriers, according to Alzforum. The new paper fills in the "how."
About one in five people carry at least one copy of APOE4. It is the most common strong risk factor for late-onset Alzheimer's. Not everyone with the gene gets sick, and researchers have long wanted to know what sets the protected carriers apart.
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The blood-brain barrier is where the trouble starts
Fibronectin is a protein that helps build and support tissue, including the walls of blood vessels. In APOE4 carriers, too much of it piles up around the small vessels that feed the brain.
That buildup damages the blood-brain barrier, the layer of cells that normally keeps unwanted substances out of brain tissue.
In mice engineered to carry the human APOE4 gene, brain fibronectin was nearly double the level seen in mice with the common APOE3 version. Blood vessels in those mice also became leakier.
The protective FN1 mutation appears to limit how much fibronectin accumulates in the first place, keeping the barrier more intact.
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"This new study takes us from a genetic clue to a disease mechanism," said Caghan Kizil, professor of neurological sciences at Columbia University and the paper's corresponding author.
What this may mean for future prevention
Alzheimer's research has long focused on amyloid plaques inside the brain. This work points at a different stage of the disease, the slow damage to blood vessels that may come years before memory loss shows up.
The Columbia team is now exploring three paths, all aimed at copying what the protective mutation does naturally. One would prevent harmful fibronectin from building up. Another would block the abnormal signals it triggers in brain blood vessels.
A third would restore the growth factor signaling that fibronectin disrupts.
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None of these approaches are available as a treatment yet. Any new therapy would need to lower the harmful fibronectin buildup without disrupting the protein's essential roles elsewhere in the body.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.