Apolipoprotein E is a lipoprotein, or a protein connected to a fat. Lipoproteins are responsible for carrying cholesterol and other fats through the bloodstream as little packages and are essential for the normal breakdown of these molecules. In particular, apolipoprotein E is a major component of specific lipoproteins called very low-density lipoproteins (VLDL). A major function of VLDLs is to remove excess cholesterol from the blood and carry it to the liver for processing.

Maintaining normal levels of cholesterol is essential for the prevention of cardiovascular diseases, including heart attacks and strokes. There are at least three slightly different versions of the APOE gene. The major versions, or alleles, are called e2, e3, and e4 (see table 1). The most common allele is e3, which is found in more than half of the population.

The APOE gene is located on the long (q) arm of chromosome 19 at position 13.2. People who inherit at least one copy of the APOE e4 allele have an increased risk of developing type 2 Alzheimer disease, which first appears later in life. Research has shown that people who inherit two copies of APOE e4 have the highest chance of developing the disease. It is not yet known how this allele affects a person's risk of Alzheimer disease; however, researchers have found that it increases the number of amyloid plaques, which are characteristic of the disease.

ApoE genotyping is sometimes used as an adjunct test to help confirm a diagnosis of probable late onset Alzheimer’s Disease in symptomatic adults. It is called susceptibility or risk factor testing because it indicates whether there is an increased risk of AD but is not diagnostic of AD. Apolipoprotein E is also associated with several cardiovascular disorders. Researchers have found that most people with familial hypercholesterolemia, a condition that causes very high levels of cholesterol and an increased risk of heart attacks and strokes, have two copies of the e2 allele.

This allele seems to be one of several genetic factors that play a part in this disorder. Another version of apolipoprotein E, the e4 allele, is a risk factor for coronary artery disease. This product is for genotyping two single nucleotide polymorphisms, here designated APOE 112 and APOE 158, resulting in amino acid substitutions at positions 112 and 158 of the protein.

The APOE genotypes

A single PCR fragment spanning the two polymorphic positions is amplified, and the Pyrosequencing analysis of the two APOE polymorphisms is performed in a single duplex reaction. See figure 1 for an illustration of the assay.

Illustration of the APOE assay. PCR primers are shown as solid arrows and sequencing primers as dashed arrows. FP: forward primer; RPB: biotinylated reverse primer; seq: sequencing primer