APP and Alzheimer disease: As the understanding of the pathological changes that occur in AD improved, research has shifted to the investigation of more specific modifications in Aβ processing, such as the cleavage of amyloid precursor protein (APP) into Aβ peptides (Aβ1–40 and Aβ1–42) and the relevance of Aβ oligomers (small aggregates of 2–12 peptides) [86,88].