In addition to the well-known amyloid cascade hypothesis of AD, other hypotheses have been proposed that include: (1) the Wnt/Glycogen Synthase Kinase 3β (GSK3β) hypothesis (Hooper et al., 2008; De Ferrari et al., 2014; Llorens-Martín et al., 2014), (2) the α-synuclein hypothesis (Moussaud et al., 2014; Yan et al., 2018), and (3) the type 3 diabetes hypothesis (de la Monte and Wands, 2008). Here, SNCA is linked to Alzheimer disease.