APP and Alzheimer disease: The second reason is that, as discussed above, AD appears to be human-specific or, at least, species-specific [152,153,154,155,156,157], i.e., human cells seem to possess unique feature(s), possibly the ability to produce iAβ in the AβPP-independent mode [156] or enact some other mechanism(s) enabling the second AD stage, that are, because of the structure of their AβPP mRNA or for other reasons, unavailable in non-human mammalian species [161,162,163].