MAPT and Alzheimer disease: We have long assumed that the neuropathological findings of aggregated α-synuclein (α-syn) into Lewy bodies and Lewy neurites define and cause Parkinson’s disease (PD) and that aggregations of amyloid (Aβ) into plaques and tau into neurofibrillary tangles define and cause Alzheimer’s disease (AD), and that the distribution of these proteins explains their clinical heterogeneity (Espay et al., 2020).