Alzheimer's disease (AD) is a progressive neurodegenerative disease with insidious onset. Clinically, it is characterized by generalized dementia, such as memory impairment, aphasia, apraxia, agnosia, impairment of visuospatial skills, executive dysfunction, and personality and behavioral changes. The etiology is still unknown. Those with onset before the age of 65 are called Alzheimer's disease. Those with onset after the age of 65 are called senile dementia.