APP and Alzheimer disease: AD is characterized by the accumulation of amyloid beta (Aβ) peptide, which is produced by abnormal proteolytic cleavage of amyloid precursor protein (APP), as well as by the formation of neurofibrillary tangles composed of tau protein and by neuronal loss, leading to learning and memory impairment (Oddo et al., 2003; Mattson et al., 2008).