[nrdvana]

Also not a biologist, but as I understand it: Every living creature synthesizes proteins. Every time you synthesize a protein, there is a tiny tiny chance that it synthesizes "backward". Backward proteins are physically incompatible with "forward" proteins, and also increase the risk that more proteins synthesize backward. It leads to a cascade of errors where lots of proteins synthesize backward and the cells and internal structures can no longer function. It's like you fall apart due to half your Lego bricks being upside-down. And, this is all a statistical probability that could occur in any moment to any living organism.

The evolutionary defenses are to break apart all incoming proteins and reassemble them yourself, and have a cycle of life that starts new organisms from scratch. Large carnivores can't hope to break apart every incoming protein, though. So, basically our lifespans and reproduction method of growing up from a single cell are the evolutionary defenses against the natural phenomenon of prions. But yes, prion disease is probably what forces all higher foodchain animals to avoid cannibalism.

[rcxdude]

This is not at all how it works. Prion diseases are not at all to do with synthesising proteins 'backwards'. It's entirely because of one protein found in the brain which has a very stable misfolded form which will induce other copies of it to misfold as well (and this misfolds all stick together into something the body struggles to break down, which is what eventually causes the damage). It's not something that can happen to just any protein (lots of other proteins do misfold or are otherwise not made correctly, all the time. But they don't induce other proteins to misfold and the body can easily break them down or otherwise get rid of them)

(in fact, the misfolded form is so stable it can survive cooking, autoclaving(!), sitting in soil for years, and digestion. The main reason it's not a big threat is that it needs to somehow get from the environment into the brain, generally via the gut, which is not a particularly easy process for an inert clump of amino acids: a significant percentage of UK residents actually have detectable levels of this prion in their gut already, but only a very small fraction will develop the disease)

[gustavus]

So that has raised an interesting question in my mind. But as far as I know the only significant case of prion disease amongst human beings, excluding CJD which seems to be generically determined, was the instance of Kuru among the Papau New Guinea tribes; however we know other societies practiced cannibalism at a certain scale such as the Aztecs in which people were eating other people all over the place, yet we don't have widespread evidence of Kuru.

Is there something distinct about Brian tissue which puts it at a higher risk for prion disease formation?

[zdragnar]

Just a bystander shooting from the hip, but does the fact that brain nerve cells aren't recycled and rebuilt but live as long as the person does mean they are more prone to accumulating bad proteins?

Other tissue like skin or muscle that regularly break down and regrow would offer a lot more opportunity for the body to filter out the prions, but once in the brain cells, there's nothing for them to do but accumulate.

[rcxdude]

It's because the prion protein is in the brain. As in, there is basically only one protein in mammals which actually has this problem (that we know of), it's not a general issue with proteins. The variants which exist are essentially because of the small variations in this protein across species, or specific inheritable mutations which make sponteneous formation of the misfolded form more likely.

(this protein, by the way, is not essential for life, but lacking it seems to slow brain development in mice)