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

• Observational (Other): Cross sectional analyses The two main variables for the analysis will be: Values of biomarker concentrations in blood and their correlations with CSF biomarkers and the development of prodromal AD for the cognitively unimpaired SCD population. Other variables of interest for the study are, among others, risk factors, cognitive status, measurements of brain structure and function, mental health, chronic diseases, environmental exposures, age and sex. Longitudinal analyses Longitudinal analyses will estimate the association between the intensity of the subjective complaint and the rate of progression between the diagnostic categories; The association of biomarkers, risk factors and other clinical variables with the rate of progression between the diagnostic categories; The association of cognitive and neuroimaging variables with the rate of progression between the diagnostic categories; The evolution of the complaint itself and its relation to the other variables described.

Primary outcomes

• CSF Aβ42/Aβ40 ratio [Through study completion, an average of 1 year]: The capacity of plasma biomarkers to predict (alone or in combination of covariates) Alzheimer's pathology

Secondary outcomes

• Cost effectiveness [Through study completion, an average of 1 year]: The ratio between the cost and predictive capacity of these variables will be considered to derive a triaging algorithm for primary care

Sex: All, ages: 55 Years to 80 Years

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.