Alzheimer disease (AD), which accounts for a severe public health problem, is the most common cause of dementia in the elderly. It is a degenerative neurologic disease that causes a functional impairment and structural alterations of the central nervous system (CNS). Its onset is sudden, and its course is progressive and slow (even slower than in inherited metabolic diseases in which neither the patient nor the family can state the exact date when the disease started). In the late stage of the disease, both physical and psychical deterioration is observed. This disease was first described in 1906 by Alois Alzheimer based on the clinical data and histopathological examination of a female patient with progressive dementia who died at 55 years of age. Since then, and taken this case into account, AD or presenile dementia is referred to as a disease whose onset occurs before the age of 50. As life expectancy increased, clinical features of the disease were observed in older patients; therefore, the term senile dementia started to be used to refer to this disease.