MAPT and Alzheimer disease: By using the ligand-based positron emission tomography (PET), abnormal dosages of the beta amyloid to tau ratio in cerebrospinal fluid (CSF) and deposition of beta amyloid in the brain can be used to diagnose the prodromal stages of AD in MCI subjects; moreover, the neurodegeneration such as atrophy of the hippocampus on magnetic resonance imaging (MRI) and hypometabolism of the posterior cingulate/precuneus, parietal and temporal regions revealed by fluorodeoxyglucose (FDG)-PET are all useful biomarkers for diagnosis of prodromal stages of AD (Albert et al., 2011).