Cohort Study of Adult Patients With Down Syndrome at Risk of Developing Alzheimer's Disease (TriAL21)

Inclusion Criteria: * Male or female 35 years old and over ; * Clinical diagnosis of Down syndrome ; * Patient attending the geriatric outpatient clinic * Patient without diagnosis of Alzheimer's disease; * Patient covered by social welfare; * Patient himself or legal guardian/representative willing and consenting to participate to the study by giving written informed consent; * Patients must have a parent, or / and other reliable caregiver who agrees to accompany him/her to all visits, provide information about the patient as required by the protocol. The parent or caregiver must be a constant and reliable informant with sufficient contact with the patient to have detailed knowledge of the patient's adaptive functioning in order to be able to complete the assessments accurately. Exclusion Criteria: * Patient presenting a contraindication to MRI in particular carrier of metal implants such as pacemakers; * Patient presenting a serious, severe or unstable pathology (left to the investigator's discretion) whose nature may interfere with the evaluation parameters; * Patient without Alzheimer's disease diagnosis but with severe dementia; * Participation in other clinical trials in the last 3 months prior to the study; * Pregnant woman.