The Chinese Familial Alzheimer's Network

Familial Alzheimer's disease group Inclusion criteria: 1. Written informed consent obtained from the participant or a legal guardian prior to any study-related procedures; 2. At least two first-degree relatives in a family have AD (clinically or by testing)，and at least 3 out of 2 generations are patients; 3. At least one family member with normal cognitive function (the age should be greater than the average age of onset of the family); 4. Pedigrees carrying FAD pathogenic genes (APP/PSEN1/PSEN2); 5. People in this family \>18 years old can be recruited; 6. Participant is cognitively normal or demented but not reaching bedridden level; 7. Participants are able to provide two reliable informants who can provide clinical information; 8. Dementia is diagnosed according to the criteria described by the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-R ); 9. 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 Association (NIA-AA) criteria ; 10. The diagnosis of MCI is made according to Petersen criteria and the classification is according to the method of Lopez et al. Exclusion criteria: 1. Dementia caused by other factors such as depression, other psychiatric illnesses, thyroid dysfunction, encephalitis, multiple sclerosis, brain trauma, brain tumor, syphilis, acquired immunodeficiency syndrome (AIDS), Creutzfeldt-Jakob disease and other types of dementias such as vascular dementia (VaD), frontotemporal dementia (FTD), dementia with Lewy bodies (DLB), and Parkinson's dementia (PDD)； 2. MRI and laboratory tests do not support or rule out a diagnosis of AD； 3. Severe circulatory, respiratory, urinary, digestive, hematopoietic diseases (such as unstable angina, uncontrollable asthma, active gastric bleeding) and cancer； 4. Participant has severe psychiatric illness or severe dementia that would interfere in completing initial and follow-up clinical assessments； 5. Participant has a history of alcoholism or drug abuse； 6. Pregnant or lactating women； 7. No reliable informant； 8. Lumbar puncture exclusion criteria：coagulation disorders or platelet counts \< 100,000 cells/μL, lumbar surgery within the last 6 months prior to lumbar puncture that interferes with anatomy of the inter-vertebral spaces, History of chronic or repeated CSF leakage following previous LP(s); 9. MRI Exclusion Criteria: electronic and magnetic metal implants such as pacemakers, artificial heart valve, metal prosthesis, metal joint, etc.; metallic foreign body in the eye; aneurysm clips in the brain. Normal control group Inclusion criteria: 1. Aged 18 (inclusive) or above; 2. Normal MMSE and MoCA evaluations. MMSE\>19 points for illiteracy, \>24 points for those educated less than 7 years, \>27 points for those educated equal to or more than 7 years. MoCA\>13 points for illiteracy, \>19 points for those educated less than 7 years, \>24 points for those educated equal to or more than 7 years. Exclusion criteria: 1. Subjects with abnormal MMSE or MoCA scores; 2. Subjects with a history of cerebral infarction, traumatic brain injury or related manifestations in MRI; 3. Other neurological diseases that can cause brain dysfunction (such as depression, brain tumor, Parkinson's disease, metabolic encephalopathy, encephalitis, multiple sclerosis, epilepsy, brain trauma, normal intracranial pressure hydrocephalus, etc.); 4. Other systemic diseases that can cause cognitive impairment (such as liver, renal and thyroid insufficiency, severe anemia, folic acid or vitamin B12 deficiency, syphilis, HIV infection, alcohol and drug abuse, etc.); 5. Mental and neurodevelopmental retardation; 6. Suffering from a disease that cannot be combined with a cognitive examination; 7. Contraindications to MRI; 8. Refuse to draw blood; 9. Refuse to sign the informed consent at baseline.