it’s almost certainly not, or you would see epidemiological evidence for chains of transmission. prion diseases require contact transmission which is all but absent from the alzheimer’s story.
I think what the parent comment is saying is, what if it isn't transmitted, what if a prion is just occurring in the brains of the people who develop alzheimers?
That seems unlikely to me, but on the other hand, the article seems to be suggesting that transferring brain proteins from people with alzheimers to people who are younger will cause them to develop alzheimers which would be roughly consistent with that.
I don't know whether that would be possible, but, for example, what if there was somehow a specific protein in the brain that could easily be misfolded to become a prion, and the eventually if people live long enough they tend to produce that prion at least once, so it occurs essentially as a result of old age, but it can theoretically also be transmitted in the manner described in the article?
I know CWD transmits from pretty much any shedding of the animal, but is that necessarily universally true?
Can we map that onto human beings who practice hygeine and don't eat leaves that another human urinated on?
You could also explain the age skewness by allowing for the fact that it takes time for the prions to replicate to the point that you notice symptoms.
Other I think this would predict: lifetime exposure to mutagens is a predictor for Alzheimer's. Alzheimer's is more heritable from the mother than the father.