MAPT and Alzheimer disease: Alzheimer's disease (AD) is pathologically defined by the presence of extracellular amyloid β (Aβ) plaques and intracellular tangles of hyperphosphorylated tau (ptau) (Mirra et al., 1991; Braak and Braak, 1991; Braak et al., 2006; Thal et al., 2002; Hyman et al., 2012).