MAPT and Alzheimer disease: Alzheimer's disease (AD), the most frequent etiology of late‐life dementia,6 is a gradual multistep brain disorder that manifests first as mild cognitive impairments, frequently with episodic memory deficits, and gradually progresses into more severe cognitive decline and dementia, reflecting a massive neuronal degeneration, specifically excessive accumulation of amyloid beta (Aβ) and its formation into plaques, followed by hyperphosphorylation and breakdown of tau from the neural microtubule skeleton and their formation into neurofibrillary tangles.