Alzheimer's Disease and Apolipoprotein E

How is Apolipoprotein E (ApoE) related to Alzheimer's disease?

ApoE is a protein which, in the blood, helps carry cholesterol and fat. The three common forms of the gene for this protein are ApoE2, ApoE3, and ApoE4. In early 1993, ApoE4 was identified as a genetic risk factor for Alzheimer's disease.

The ApoE4 gene may play a role in one third of the cases of Alzheimer's disease (AD). However, this major finding will not immediately affect diagnosis or treatment of AD. The real hope is that within the next ten years, scientists may be able to block the action of the gene, improve treatments or even prevent disease in those individuals with the gene.

What is Alzheimer's disease?

Alzheimer's disease affects the structure and function of the brain, causing progressive loss of memory, language, and ability to care for oneself. Making a diagnosis of AD in life requires that a physician obtain a detailed medical history, physical examination plus additional medical tests.

At present, a test to see if you have the ApoE4 gene will not determine whether you have Alzheimer's disease. In fact, no single test can tell a physician that a person has AD. Other possible causes of memory problems (for example, strokes or chronic alcoholism) must be ruled out.

What is the ApoE test? What can it tell us?

The ApoE test is a blood test. Genetic material (DNA) is extracted from an individual's blood sample to assess the ApoE genes. A person inherits either an E2, E3, or E4 gene from each parent.

Individuals with one or two ApoE4 genes may have an increased risk of developing Alzheimer's disease compared to those who have no ApoE4 genes. In some ways, the situation is similar to smoking and lung cancer. Smoking increases a person's risk of developing lung cancer, yet some people smoke heavily and never get cancer. Similarly, some individuals with the E4 gene will never develop AD and others with no E4 will go on to develop the disease. ApoE4 is associated with about a third of all cases of AD.

What are the limitations of the ApoE test?

The ApoE test will not tell your doctor, for certain, that you have Alzheimer's disease. It can only predict the amount of increased risk for developing the disease. Nor will the ApoE test help your doctor to decide on treatments for AD or memory problems. At present, the test is primarily a research tool for further investigation into the understanding, treatment and prevention of Alzheimer's disease.

Should I be tested?

Genetic testing must always involve thorough consideration and understanding of possible benefits, risks or harmful consequences resulting from test findings. While it is up to each individual to make his or her own decision, genetic counseling and consultation with medical experts is strongly recommended before ApoE testing.

Additional information can be obtained from your local Alzheimer's Association Chapter or the Alzheimer's Disease Education and Referral Center.