Among the biomarkers that are currently known for AD diagnosis, the most relevant one is the Aβ peptide, showing a key participation in the development of AD, as described in the amyloid cascade hypothesis [4,18,19] shown in Figure 2A. This hypothesis posits that Aβ is produced by the processing of the amyloid precursor protein (APP), a transmembrane protein located in the neuronal cell membrane [20,21]. The gene discussed is APP; the disease is Alzheimer disease.