Alzheimer's disease (AD) is the most prevalent form of dementia and the number of AD patients is expected to increase as human life expectancy improves. The deposition of β-amyloid protein (Aβ) in the extracellular matrix and neurofibrillary tangles intracellularly are pathologic hallmarks. Since the precise pathophysiology of AD has not been clearly elucidated yet, effective treatment is not available. Thus the development of valid AD biomarkers is imperative for early diagnosis and for monitoring disease progression and therapeutic responses.