APPL1 and Alzheimer disease: Alzheimer's disease (AD) is the second most common neurodegenerative disorder characterized by the formation of extracellular Aβ42 plaques (amyloidogenic cleavage of APPL protein) by β and γ-secretase and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein (Binder et al., 2005; O'Brien and Wong, 2011).