Apolipoprotein E (APOE) is a protein involved in the metabolism of lipids and cholesterol in the body. Research on APOE focuses on its role in various health conditions, particularly Alzheimer's disease. A variation of the APOE gene, called APOE4, is a major genetic risk factor for late-onset Alzheimer's disease. Other areas of research on APOE include its role in cardiovascular disease, inflammation, and immune response. Understanding the functions and implications of APOE can provide insights into the development and treatment of various diseases.