Alzheimer's Disease and Genes : ApoE Testing, Diagnosis

by National Institute on Aging

(Page 2 of 2)

A blood test is available that can identify which APOE alleles a person has. However, because the APOE e4 gene is only a risk factor for AD, this blood test cannot tell whether a person will develop AD or not. Instead of a yes or no answer, the best information a person can get from this genetic test for APOE is maybe or maybe not. Although some people want to know whether they will get AD later in life, this type of prediction is not yet possible. In fact, some researchers believe that screening measures may never be able to predict AD with 100 percent accuracy.

In a research setting, APOE testing may be used to identify study volunteers who may be at a higher risk of getting AD. In this way, researchers can look for early brain changes in some patients. This test also helps researchers compare the effectiveness of treatments for patients with different APOE profiles. Most researchers believe that the APOE test is useful for studying AD risk in large groups of people but not for determining one person's individual risk. Predictive screening in otherwise healthy people will be useful if an accurate/reliable test is developed and effective ways to treat or prevent AD are available.

In diagnosing AD, APOE testing is not a common practice. The only definite way to diagnose AD is by viewing a sample of a person's brain tissue under a microscope to determine if there are plaques and tangles present. This is usually done after the person dies. However, through a complete medical evaluation (including a medical history, laboratory tests, neuropsychological tests, and brain scans), well-trained doctors can diagnose AD correctly up to 90 percent of the time. Doctors look to rule out other diseases and disorders that can cause the same symptoms of AD. If no other cause is identified, a person is said to have "probable" or "possible" AD. In some cases, APOE testing may be used in combination with these other medical tests to strengthen the diagnosis of a suspected case of AD. Currently, there is no medical test to establish if a person without the symptoms of AD is going to develop the disease. APOE testing as a patient screening (predictive) method is not recommended.

Concerns About Confidentiality

APOE testing, and indeed all genetic testing, raises ethical, legal, and social questions for which we have few answers. Generally, confidentiality laws protect APOE information gathered for research purposes. On the other hand, information obtained in APOE testing may not remain confidential if it becomes part of a person's medical records. Thereafter, employers, insurance companies, and other health care organizations could find out this information, and discrimination could result. For example, employment opportunities or insurance premiums could be affected.

Genetic Counseling

Depending on the study, research volunteers may occasionally have the opportunity to learn the results of their APOE testing. The meaning of these results is complex. Since the results of APOE testing can be hard to understand, and more importantly, devastating to those tested, the NIA and the Alzheimer's Association recommend that research volunteers and their families receive genetic counseling before and after testing, if they have the option of learning the results.

People who learn through testing that they have an increased risk of getting AD may experience emotional distress and depression about the future, because there is not yet an effective way to prevent or cure the disease. Through counseling, families can learn about the genetics of AD, the tests themselves, and possible meanings of the results. Due to privacy, emotional, and health care issues, the primary goal of genetic counseling is to help people explore and cope with the potential consequences of such knowledge.

Experts still do not know how limited information about AD risk can benefit people. Among the issues are privacy and confidentiality policies related to genetic information and AD, and the small number of genetic counselors now trained in neurodegenerative disorders. In addition, little is known about how stigma associated with an increased risk for AD may affect people's families and their lives.

Research Questions

Learning more about the role of APOE e4 and other risk factor genes in the development of AD may help scientists identify who would benefit from prevention and treatment efforts. Age, still the most important known risk factor for AD, continues to be associated with the disease even when no known genetic factors are present. Research focusing on advancing age may help explain the role that other genes play in most AD cases. Many AD researchers are studying the genetics of AD. In addition, researchers, ethicists, and health care providers are developing policies about the appropriate use of genetic testing and counseling for AD.

About the Author

www.nia.nih.gov
NIA, one of the 27 Institutes and Centers of NIH, leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life. In 1974, Congress granted authority to form NIA to provide leadership in aging research, training, health information dissemination, and other programs relevant to aging and older people.