MAPT and early-onset autosomal dominant Alzheimer disease: Role of synaptic function defect in Alzheimer's disease (AD): Alzheimer's disease (AD) is one of the most common neurodegenerative disorders identified by a continuous loss of cognition, the existence of two hallmark lesions, senile plaques (SP), and neurofibrillary tangles (NFT), which result from the build-up and deposition of β-amyloid peptide (Aβ) and the aggregation of hyperphosphorylated tau protein, respectively.