AILSA CHANG, HOST:
People who inherit one very rare gene mutation are almost guaranteed to develop Alzheimer's before they turn 50, except for Doug Whitney.
DOUG WHITNEY: I'm 75 years old, and I think I'm functioning fairly well. I'm still not showing any of the symptoms of Alzheimer's.
CHANG: NPR's Jon Hamilton reports on what scientists are learning from a man who is an exception to a genetic rule.
JON HAMILTON, BYLINE: Early onset Alzheimer's is everywhere in Doug Whitney's family.
D WHITNEY: Ten of my mother's 14 brothers and sisters had the Alzheimer's gene. None of them lasted past 60 years old.
D WHITNEY: Whitney's wife, Ione, saw this up close.
IONE WHITNEY: We went home for Thanksgiving, and his mom couldn't remember the pumpkin pie recipe. And a year later when we went back, she was already wandering off and not finding her way back home.
HAMILTON: She was in her 40s at the time. The affected family members all carried a mutated version of a gene called presenilin 2. The variant causes a person's brain to accumulate beta-amyloid and tau proteins, the hallmarks of Alzheimer's. Doug Whitney assumed he didn't have the mutation when he was still fine at 60, but he wanted to help others, so he volunteered for a study of families with early Alzheimer's.
D WHITNEY: I submitted my blood samples, and to my great surprise, I came back positive for the Alzheimer's gene. It was quite a shock.
HAMILTON: It was also a shock for scientists, including Jorge Llibre of Washington University in St. Louis. Llibre says Whitney is just the third person known to have dodged the effects of an early Alzheimer's mutation.
JORGE LLIBRE: It's so important - right? - because it's telling us that something is going on that is protecting these people.
HAMILTON: The first two came from a group in Colombia with mutations to the presenilin 1 gene. Whitney is the only person known to have resisted a mutation in the presenilin 2 gene. Llibre says all three had lots of beta-amyloid protein in their brains, but he says they didn't have much tau, the other Alzheimer's protein.
LLIBRE: So one key element of the disease that is having the tau protein spread through the brain - that was not happening.
HAMILTON: Tau is a misfolded protein that tends to appear in one place then spread. Llibre says in Whitney's brain, tau was confined to a small area involved in visual perception.
LLIBRE: There is something that is protect him from tau spreading.
HAMILTON: Now scientists are trying to figure out what. One thing they've learned is that Whitney's brain contained high levels of heat shock proteins, which help protect cells from high temperatures. Llibre says they also seem to prevent tau from misfolding into the toxic form associated with Alzheimer's.
LLIBRE: It may be the case that those proteins are preventing more tau to be misfolded and then spread through the brain.
HAMILTON: Llibre says the findings, which appear in the journal Nature Medicine, could point the way to new treatments for Alzheimer's.
LLIBRE: The main point is that if we are able to learn what is causing the protection here, then we could translate that to therapeutic approaches and apply that to the more common forms of the disease.
HAMILTON: Scientists told Doug Whitney that the high levels of heat shock proteins in his brain might be the result of his life experience.
D WHITNEY: I spent 20 years in the Navy, most of it in the hot spots like the engine rooms of ships. A hundred and ten degrees is nothing on a ship.
HAMILTON: Whitney plans to continue making his brain available to scientists, in hopes they will find a way to protect other brains from Alzheimer's.
D WHITNEY: I would love to see that happen while I'm still around.
HAMILTON: And still thinking clearly. Jon Hamilton, NPR News.
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