MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized pathologically by the presence of extracellular amyloid plaques containing the amyloid-β peptide (Aβ) and intracellular neurofibrillary tangles (NFTs) containing hyperphosphorylated microtubule-associated protein tau and loss of synapses and neurons in select brain regions [1–3].