About 50 people will be asked to take part in this study at this location. This will include participants with early-onset AD and their parents and siblings. Participants will be asked to: Sign this consent form or have a Legally Authorized Representative sign and provide the participant' health history. The study staff will review the participant's medical history and test results to see if the participant can be part of this study, The study staff will need to know any over-the-counter or prescription drugs, vitamins, or herbs taken by the participant. The study staff will discuss what is required to be part of this study. Participants cannot take part in this study if they have: Family history of early or late-onset Alzheimer's disease, Uncontrolled concurrent illness including psychiatric illness or situations that would limit compliance with the study requirements or the ability to willingly give written or verbal consent. If the participant agrees to take part in this study, one 8mL blood sample (about 2 teaspoons) will be collected from them. If the participant is receiving a clinically indicated blood draw, the blood collections for this study will occur at the same time. Participants may be required to have a research-specific blood draw if they are not scheduled for a blood draw during a regularly scheduled visit.