β-AARC: Cohort Study for the Identification of Blood-based Biomarkers in a Population With Subjective Cognitive Decline

Inclusion Criteria: 1. Cognitively unimpaired persons with SCD as well as individuals with MCI. 2. To sign the study informed consent form, approved by the corresponding authorities. 3. Participation (in-person at the institution or telephonically) of a relative to inform on the participant subjective memory decline and on the clinical interview\*. 4. Men and women between 55 and 80 years old 5. Memory Alteration Test (M@T) ≤45 6. Good knowledge of the either Spanish or Catalan language and being literate. Exclusion Criteria: 1. Presence of clinically relevant psychiatric disorder according to the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-V) criteria: major depressive disorder, generalized anxiety disorder, schizophrenia and bipolar disorder, or any other condition that might impact cognition or performance on cognitive assessments as judged by the investigator 2. Parkinson's disease, epilepsy in treatment and with frequent seizures (\> 1 / month) in the last year, multiple sclerosis or other neurodegenerative disease. 3. Contraindication to perform an MR scan: claustrophobia, pacemaker, metallic implants, etc. 4. Contraindication to lumbar puncture 5. Acquired brain injury: history of cranioencephalic trauma with gross parenchymal or extra axial lesion, hemorrhagic ischemic stroke, brain tumors and other aetiologies that can cause acquired brain damage (chemotherapy or brain radiotherapy). 6. Investigator's criteria: Subjects that show any condition that, in the opinion of the investigator, could interfere in the proper execution of the study procedures and / or in their future permanence in the study.