MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer’s disease (AD) is biologically defined by the cerebral accumulation of amyloid-beta (Aβ) containing plaques and neurofibrillary tangles (NFT) comprised of hyperphosphorylated tau, a process that begins decades before the onset of mild cognitive impairment (MCI) and dementia [1, 2].