MAPT and early-onset autosomal dominant Alzheimer disease: Alzheimer's disease (AD) is the most prevalent tauopathy,1 characterized by the co‐occurrence of amyloid β (Aβ)‐positive extracellular plaques and intracellular neuronal tau pathology affecting both neurites (neuropil threads and neuritic plaques) and cell‐body (neurofibrillary tangles, NFTs).2