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Alzheimer's has was thought to be caused by inflammatory events in the brain that led to the formation of amyloid plaques. But drugs that treat amyloid don't work against Alzheimer's. Maybe now we know why.

We’re still very unclear about what causes Alzheimer’s disease. Because it affects the mind it’s a uniquely frightening prospect, and any news we can get on how it works or what we can do about it is a step in the right direction.

Trouble is, it looks like we might have gone a little in the wrong direction.

In Alzheimer’s, you find pieces of tissue in the brains of sufferers called amyloid plaques. These also show up in the brains of people with Parkinson’s and even the degenerative encephalopathic disease CJD. Are you thinking what I’m thinking?

You, and a lot of scientists. What if amyloid plaques are the causative agent? By somehow interfering with blood flow, or by some chemical effect, amyloid plaques could be the cause, or a crucial part of the mechanism of these diseases. Get rid of the plaques and you might be able to get rid of the symptoms.

Unfortunately, it now looks like that is not the case.

Rather than amyloid plaques, the real cause of Alzheimer’s now appears to be something else altogether. Amyloid is a result, not a cause — it’s something else that happens to you when you have Alzheimer’s or other degenerative neurological diseases, but it’s not the main driving force.

Instead, the real cause seems to be a protein called Tau.

Tau proteins are found all over the CNS but especially in the brain and they have a very specific job; they stabilize microtubules. As much as this sounds like something Doctor Who might struggle with during a particularly underfunded episode - pass me the sonic screwdriver, I have to stabilize this microtube! - it’s actually a desperately important function, because of the role that microtubules play in brain function.

Microtubules are a part of the structure of all your cells. They form the cell skeleton, or cytoskeleton. They’re hollow spirals made of protein copolymers and they do a range of jobs in addition to holding cells in shape, depending where you find them. Find them in the brain, and they’re holding the elongated, branched structures of neurons in their right shape and their right place.

When tau proteins stop supporting them properly, you’d expect them to start to collapse. The metabolic functions that depend on their ability to be stable and mobile would cease. And that is what happens. It happens in the cells with the most connections, which in humans is the neurons in the areas of the brain related to abstract thought, creativity, the creation of new ideas and the lawying down of new memories. Sounds right. And the effects are most devastating, most soon, in the neurons whose connections are still tentative where new memories are being laid down in long-term memory storage. That makes sense too, and it fits with what we know about the symptoms and progress of the disease.

But there's more to the damage Tau can do than which neurons are harmed first. The brain is divided into areas with specialist functions and it's this that has made the scientists behind the breakthough study, published in Brain in March of this year, recommend that research attention turn from amyloid to Tau. 

Abnormal Tau starts accumulating first in the hippocampus, the part of the brain that deals with memory, before moving to the cortex which deals with thought and ideas. Amyloid does the opposite. That's a strong argument that Tau is the real cause.

Continue reading after recommendations

  • Kevin Punsky, Mayo Clinic Study of Thousands of Brains Reveals Tau as Driver of Alzheimer’s Disease,
  • Photo courtesy of Generaal Gibson via Flickr:
  • Photo courtesy of Generaal Gibson via Flickr:
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