This study will recruit from three experimental groups: (1)The DS (adult) group will consist of 15 DS subjects aged 21 and older who do not qualify for the diagnosis of dementia at the beginning of the study. (2)The DS/AD group will consist of 15 DS subjects aged 40 and older who do qualify for the diagnosis of dementia by Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria. Diagnoses will be by standard consensus review of all cases. (3)Normal control (NC) adult will consist of 10 cognitively normal, non-DS individuals, age-matched to the DS group. Blood will be collected to assess apolipoprotein E (ApoE) genotype. Participation in the dried blood spot collection (DBSC) will be an optional sub-study. Only participants and/or their caregivers/legally authorized representatives indicating they wish to have DBSC performed on the consent will provide specimens.