Apolipoprotein E (ApoE) is a protein that plays a crucial role in lipid metabolism. It is primarily involved in the transport and clearance of fats and cholesterol in the bloodstream. ApoE is produced mainly in the liver and brain, and it helps to bind lipoproteins to cell receptors, facilitating the uptake of lipids by cells. There are three major isoforms of ApoE: ApoE2, ApoE3, and ApoE4. These isoforms differ in their genetic structure and influence an individual's risk for certain diseases, particularly Alzheimer's disease. The presence of the ApoE4 variant is associated with an increased risk of developing Alzheimer's, while ApoE2 may offer some protective effects.