Study on Biomarkers for Early Diagnosis of Alzheimer's Disease

Inclusion Criteria: * Written informed consent obtained from participant or legal guardian prior to any study-related procedures. * Aged 18 (inclusive) or older. * Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-R). The diagnosis of AD is made using the National Institute of Neurologic and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS- ADRDA) or National Institute on Aging and the Alzheimer's Assocation (NIA-AA) criteria. A diagnosis of mild cognitive impairment (MCI) is assigned according to Petersen criteria. A diagnosis of pre-MCI group is assigned by β-Amyloid positive or APOE ε4 carrier or complains of cognitive impairment, but not up to MCI or cognitive impairment. Normal cognitive function assessed/evaluated by MMSE, CDR and other cognitive function scales. * Follow up 5 years and collect the information. Exclusion Criteria: * Under age 18. * Medical or psychiatric illness that would interfere in completing initial and follow-up visits. * No one can serve as a study informant. * With current or past neurological or psychiatric illnesses such as schizophrenia, epilepsy, brain tumors, severe head trauma and other diseases which can induce dementia. * Refused to complete a cognitive test and provide biospecimen. * With history of alcohol or drug abuse.