The purpose of the Trial-Ready Cohort - Down Syndrome (TRC-DS) is to enroll 120 healthy adults with Down syndrome (DS), between the ages of 25-55, into a trial ready cohort (TRC), and up to 550 participants in total including co-enrolled in the Alzheimer Biomarkers Consortium - Down Syndrome (ABC-DS) study. Participants enrolled in the TRC-DS will undergo longitudinal cognitive and clinical assessment, genetic and biomarker testing, as well as imaging and biospecimen collection. Using these outcome measures, researchers will analyze the relationships between cognitive measures and biomarkers of Alzheimer's disease (AD) to identify endpoints for AD clinical trials in DS that best reflect disease progression.

To learn more about the study and participating sites, visit our study website at: https://www.trcds.org/.

TRC-DS is collaborating with the Alzheimer's Disease Biomarker Consortium-Down Syndrome (ABC-DS) to allow study participants to be concurrently enrolled in both ABC-DS and TRC-DS, referred to as "co-enrollment". ABC-DS is a longitudinal, observational research study that is overseen at University of Pittsburgh Coordinating Center. ABC-DS participants who express interest in potentially joining a clinical trial in the future and who meet TRC-DS eligibility criteria, may choose to co-enroll in TRC-DS at an ABC-DS Site. Co-enrolled participants will adhere to the ABC-DS protocol and schedule of activities, but agree to share their data with the TRC-DS team and to receive invitations for future participation in clinical trials. Fore more information on ABC-DS please visit https://www.nia.nih.gov/research/abc-ds or http://abcds.pitt.edu/.

Inclusion Criteria:

1. Diagnosis of DS (including trisomy 21, mosaic trisomy 21, Robertsonian translocation trisomy 21 or partial trisomy 21) (as confirmed by genetic testing or medical record review)
2. Provision of signed and dated informed consent form; this includes adults with DS who can provide consent, or for whom an LAR provides consent on behalf of the individual to participate. Adults with DS who cannot consent must sign and date an assent accompanied with a signed and dated consent by legally authorized representative (LAR).
3. Stated availability and willingness to comply with all study procedures and availability for the duration of the study or until referred to a clinical trial
4. Male or female, aged 25-55 inclusive
5. In good general health as evidenced by medical history with no diagnosis of dementia
6. Permitted CNS-active medications, stable in dose for at least 4 weeks or longer. If new medications have been started, medical monitoring team will review on case by case basis to recommend timing of baseline cognitive testing
7. Adequate visual and auditory acuity to allow neuropsychological testing
8. Mental Age of 4 years or greater (based upon the Kaufman Brief Intelligence Test, Second Edition, KBIT-2, verbal age equivalent, or based upon medical records)
9. Ability to complete KBIT-2 with IQ equal to or greater than 40
10. Must speak English or Spanish fluently
11. Must have a reliable Study Partner (may be caregiver, sibling, parent) who is capable of providing correct information about the participant's clinical symptoms and history

Exclusion Criteria:

1. Any significant disease or unstable medical condition that could affect participation (i.e., unstable psychiatric disease, unstable cardiac problems, chronic renal failure, chronic hepatic disease, severe pulmonary disease)
2. Participants in whom magnetic resonance imaging (MRI) is contraindicated including, but not limited to, those with a non-compatible pacemaker, presence of MRI-incompatible metallic fragments near the eyes or spinal cord, or cochlear implant (Dental fillings do not present a risk for MRI)
3. Participants unable to complete MRI procedure
4. History, within the last 5 years of a primary or recurrent malignant disease with the exception of non-melanoma skin cancers, resected cutaneous squamous cell carcinoma in situ, basal cell carcinoma, cervical carcinoma in situ, or in situ prostate cancer with normal prostate-specific antigen post-treatment
5. Clinically significant abnormalities in B12 or TFTs that might interfere with the study. A low B12 is exclusionary, unless follow-up labs (homocysteine (HC) and methylmalonic acid (MMA)) indicate that it is not physiologically significant. A high TSH is exclusionary unless follow up T3/T4 levels indicate that it is not physiologically significant.
6. Clinically significant abnormalities in screening laboratories
7. For participants undergoing CSF collection: a current blood clotting or bleeding disorder, or significantly abnormal PT or PTT at screening or if on anti-coagulation therapy (e.g. warfarin)
8. Concurrent participation in a clinical trial for an investigational product or concurrent participation in longitudinal study with overlapping outcome measures/procedures is prohibited with the exception of ABC-DS co-enrollment or as approved by project director
9. Participants whom the investigator deems to be otherwise ineligible. The Investigators should consult with the Coordinating Center on any issues that may disqualify the participant from participation in future clinical trials to determine whether enrollment into TRC-DS would be appropriate

120 non-demented adults with Down syndrome and up to 550 participants in total including co-enrollment the Alzheimer Biomarkers Consortium - Down Syndrome (ABC-DS)