These [clinical trial] failures, combined with the still-compelling reasons to think that amyloid is indeed a major part of the disease, have led to hypotheses that would square all these conflicting findings: perhaps amyloid really is the cause of Alzheimer’s, but not the form of amyloid we’ve been looking at. The real cause could be well upstream, in small soluble oligomers of the protein that are the earlier bad actors in the disease.