Additional Study Information: This research study aims to obtain a greater understanding of the causes of cognitive decline in Alzheimer's disease. We are currently enrolling male and female participants (ages 55 years and older) with Alzheimer's disease, mild cognitive impairment, or healthy controls. Enrolled participants will undergo a small blood draw (about 8 teaspoons) at our clinic and a brief interview about their health status with our research assistant. This research study will involve a single visit for a total of 2.5 hours (some assessments may also be performed remotely), and you will be reimbursed up to $100 for your travel/transportation and $35 for your participation.