ApoE Genotyping

1. The transport of lipids from where they are made or absorbed to the tissues where they are stored.
2. The transport of cholesterol and other lipids from the body's organs to the liver for excretion. ApoE also plays a role in lipoprotein metabolism. It helps clear very low-density lipoprotein (VLDL) and chylomicrons, the large lipoproteins that are responsible for the initial transport of dietary lipids to the liver, from the bloodstream.

This test looks at a person's DNA to determine what combination of ApoE forms (genotype) is present. The ApoE gene exists in three different forms (alleles) – e2, e3, and e4 – with e3 being the most common allele, found in 60% of the general population. Everyone inherits a pair of ApoE genes that is some combination of these three.

ApoE e3/e3 is the most common genotype. ApoE e4 (e4/e4 and e4/e3) is found in 25% of the population and is associated with an increased risk of atherosclerosis. People with these genotypes could be predisposed to an exaggerated elevation of LDL-C ("bad cholesterol") and triglycerides when their diet is high in saturated fat.

ApoE e4 has also been associated with an increased risk of late onset Alzheimer's disease (AD) – AD that develops after the age of 65. This effect is additive in that one copy of e4 (e2/e4 or e3/e4) carries some increased risk and two copies of e4 (e4/e4) are associated with an even greater risk of developing AD. It is important to note, however, that this risk is only relative. Most individuals with ApoE e4 will never develop AD and there are many AD patients who are e4 negative.

People with the ApoE e2 allele tend to have lower LDL-C levels but elevated triglycerides. ApoE e2 is also associated with type III hyperlipoproteinemia/hyperlipidemia (HPL III or familial dysbetalipoproteinemia), a rare inherited disorder that causes fatty yellowish deposits on the skin called xanthomas, increased triglycerides in the blood, and atherosclerosis that develops at an early age.