Additional Study Information: Apathy is a very common symptom experienced by people with Alzheimer's disease, and includes a lack of motivation and loss of interest in many activities. Patients and their caregivers often find apathy to be particularly distressing. This study aims to obtain a greater understanding of the causes of apathy in Alzheimer's disease. We are currently enrolling male and female participants (ages 50 years and older) with Alzheimer's disease. Enrolled participants will undergo a small blood draw (2-3 teaspoons) at our clinic and a brief interview about their health status with our research assistant. This study will involve a single visit for a total of 2.5 hours, and you will be reimbursed for your travel (or we will arrange travel for you) and $50 for your participation.