No way this was known before. There may be certain correlations but you have to realize this research effort is different. In controlled experiments if you as the experimenter can "cause" something to happen then you've skipped past the correlation != causation mantra that every Tom, Dick and Jane keeps chanting without fully understanding. At this point you've found causation.

Causal evidence of Alzheimer's? I don't think that's ever been known. The worst case scenario after finding this is that they find out that there's multiple causative sources of Alzheimer's.