The problem is viewing individual papers as the unit of truth in science. The "self-correcting" nature of science will actually reject entire papers, and entire directions of inquiry. Including, maybe, a casual relationship between beta amyloid and AD, but maybe not.
The other key part of science is holding everything in a state of uncertainty. There's some "facts" but mostly just hints and clues. And with Alzheimer's disease in particular we are trying to make progress with completely inadequate vision; we really can't even measure so much of what we want to measure. Feynman said it back in the 1960s, too, physicists have failed to deliver the tools to biologists to really measure what needs to be measured. There have been advancements, and DNA sequencing technology in the past decade has been turned into the most clever sorts of information theoretic microscopy by combining DNA sequences with many other biochemical processes. But we as a species still can not measure a lot of the things we'd like to measure.