Apolipoprotein-E (apoE) is a protein component of plasma lipoproteins. Three common ApoE alleles have been identified: ApoE2, ApoE3, and ApoE4. The corresponding three major isoforms, E2, E3, and E4, are recognized according to their relative position after isoelectric focusing. ApoE mediates the binding, internalization, and catabolism of lipoprotein particles. It can serve as a ligand for the LDL (Apo B/E) receptor and for the specific Apo-E receptor (chylomicron remnant) of hepatic tissues. Defects in Apolipoprotein E result in familial dysbetalipoproteinemia, or type III hyperlipoproteinemia (HLP III), in which increased plasma cholesterol and triglycerides are the consequence of impaired clearance of chylomicron and VLDL remnants.