RecruitingTrial-Ready Cohort-Down Syndrome (TRC-DS)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/.