APP and Alzheimer disease: Furthermore, soluble oligomeric forms of amyloid β-protein are the primary toxic species (Haass and Selkoe, 2007; Selkoe and Hardy, 2016) that have been shown to cause synaptic damage and neuronal cell death in both an APP knock-out mouse model and post-mortem human brains from patients with AD (Ding et al., 2019; Rolland et al., 2020).