It was found that Aβ42 is hydrophobic and tends to accumulate, forming amyloid plaques rather than Aβ40.20,21 Relatively high levels of BACE1 were detected in sporadic AD brains, accelerating the first step (the rate-limiting one) in the generation of Aβ from APP.22,23. Here, BACE1 is linked to Alzheimer disease.