What is the APOE Gene?

The APOE gene is the only clinically accepted genetic risk factor for late onset Alzheimer’s disease. Every person inherits two copies (one from each parent) of the APOE gene. Each copy of the APOE gene exists in one of three forms, or alleles: ε2, ε3, or ε4. Therefore, every individual possesses one of the following six possible APOE combinations:

How Does APOE Affect My Risk?

• The ε2 form is relatively rare and may provide some protection against Alzheimer’s disease.
• The ε3 form is the most common and may have a neutral role in Alzheimer’s disease.
• The ε4 form increases the risk of the disease.
• Inheriting the ε4 allele doesn’t mean that a person will definitely develop Alzheimer’s disease. It is merely a risk factor gene.

What is the Normal Function of the APOE Gene?¹

The APOE gene provides instructions for making a protein called apolipoprotein E. This protein combines with fats (lipids) in the body and is known as a lipoprotein. Lipoproteins are responsible for packaging cholesterol and other fats, carrying them through the bloodstream, and delivering them to the appropriate locations in the body for processing and use.¹

What Role Does APOE-ε4 Play In Alzheimer’s Disease?

The brains of people with Alzheimer’s disease have increased amounts of two abnormal structures:

• Beta-amyloid plaques, which are dense deposits of protein and cellular material. These plaques accumulate outside and around nerve cells.
• Neurofibrillary tangles, which are twisted fibers that build up inside the nerve cells.

Plaques and tangles usually develop as a person ages, beginning in areas devoted to learning and memory and gradually spreading to other areas. They develop much more, however, in those with Alzheimer’s disease. Though researchers have yet to identify the precise mechanism by which the APOE ε4 form affects plaque and tangle development, they have discovered a definite association between the presence of the ε4 form and an increase in plaques and tangles.

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¹Content from Genetics Home Reference Public Information from the U.S. National Institutes of Health