APP and Alzheimer disease: AD results from the incorrect proteolysis of the amyloid precursor protein (APP), developed in about 10–20 years, which causes the extracellular accumulation of aggregates of amyloid β (Aβ) substance, the amyloid plaques, and the interneural accumulation of neurofibrillary tangles of the hyperphosphorylated tau protein in encephalic areas such as the hippocampus limbic system, entorhinal and temporal cortex.