Simple blood test may spot Alzheimer's early

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: MCI group : * ≥ 70 years * MCI diagnosis : New criteria (Petersen, PORTET\*) 1. cognitive complaint from the patient, family, or both, 2. report by the subject or reporter of a decline in cognitive or functional performance, relative to previous abilities, 3. cognitive disorders evidenced by clinical evaluation: impairment in memory or another cognitive domain, 4. cognitive impairment without any repercussion on daily life, even if the subject reports difficulties concerning complex daily activities, 5. no dementia * Having signed an informed consent form * Fluent in French AD group : * ≥ 45 years * AD diagnosis (DSM IV-TR et NINCDS-ADRDA) * Mild to moderate (MMSE \> 15) * Having signed an informed consent form * Caregiver/informant to provide information on patient Exclusion Criteria: * Normal cognitive function * Major depression (according to the DSMIV-TR or MINI or Geriatric depression Scale\> 20/30) * Genetic form of AD (genetic mutation known) * All other diseases that could interfere with cognitive assessment (Epilepsy, Parkinson's disease, schizophrenia, other dementia) * Major sensory deficits that could interfere with cognitive assessment (visual and auditory) * Diseases involving the short-term survival (advanced cancer, unstable heart disease, severe hepatic/respiratory/renal failure) * Contraindication for MRI, for lumbar puncture (i.e. anticoagulant agents) * Use of any experimental agent for the duration of the study * Participation to other biomedical research that could interfere with principal objective of the study * For MCI patient, use of IchE or memantine medication before inclusion * Less than 4 years of education * Illiteracy, is unable to count or to read * Pregnant women * Non health insurance affiliation * Private subjects of freedom by legal or administrative decision * Contraindication for MRI examination: * Claustrophobic subject * Carrying a cardiac pacemaker * Presence of any ferromagnetic metallic implants or foreign bodies (carrying an internal electrical/magnetic device, carrying a valvular prosthesis) * Carrying a ventricular valvular Exclusion criteria specific to the lumbar puncture: • Taking anticoagulant agents