Diseases such as cystic fibrosis, muscular dystrophy, and Huntington’s disease are single-gene disorders. If a person inherits the gene that causes one of these disorders, he or she will usually get the disease. Alzheimer’s disease, on the other hand, is not caused by a single gene.
The two basic types of AD are familial and sporadic. Familial AD (FAD) is a rare form of early-onset AD, affecting less than 10 percent of AD patients. The majority of AD cases are sporadic, late-onset, usually developing after age 65. More than one gene mutation can cause AD, and genes on multiple chromosomes are involved.
Late-onset AD has no known cause and shows no obvious inheritance pattern. However, in some families, clusters of cases are seen. Although a specific gene has not been identified as the cause of late-onset AD, genetic factors do appear to play a role in the development of this form of AD. Only one risk factor gene has been identified so far. Researchers have identified an increased risk of developing late-onset AD related to the apolipoprotein E (APOE) gene found on chromosome 19. This gene codes for a protein that helps carry cholesterol in the bloodstream. The APOE gene comes in several different forms, or alleles, but three occur most frequently: APOE e2, APOE e3, and APOE e4. People inherit one APOE allele from each parent. Having the e4 allele is a risk factor for AD, but it does not mean that AD is certain. The e3 allele is the most common form found in the general population and may play a neutral role in AD. The rarer e2 allele appears to be associated with a lower risk of AD. The exact degree of risk of AD for any given person cannot be determined based on APOE status.
It is possible to evaluate your predisposition to develop Alzheimer’s disease and make lifestyle choices that reduce your risk factors. More and more evidence is emerging that proves environmental factors play a significant role in determining if the disease will develop and progress.
Use the internet to do research on genetic conditions and prevention strategies. Some useful sites are: www.alzheimersprevention.org , www.alzheimers.org , www.geneticalliance.org , and www.medlineplus.gov and www.mydna.com .
Learn as much as you can about your family health history, especially about your siblings, parents, and grandparents.
Share information with your physician. He or she needs to be aware of your family history in order to help you make medical decisions.
Consult a genetic counselor. Genetic counselors provide information and support to families who may be at risk for a variety of inherited conditions. They identify families at risk, analyze inheritance patterns and risks of recurrence and discuss options with the family. Locate a counselor at the National Society of Genetic Counselors at www.nsg.org.
Have a memory screening done on a regular basis, as part of your annual physical. Many memory difficulties are due to correctable conditions, such as vitamin deficiencies or stress.
Make healthy lifestyle choices. By using programs like the APFI’s Four Pillars of Prevention it is possible to minimize the risk factors and prevent memory loss!
The National Institute on Aging (NIA) has launched a major study to discover remaining genetic risk factors for late-onset AD. Geneticists from the NIA’s Alzheimer’s Disease Centers are working to collect genetic samples from families affected by multiple cases of late-onset AD. Researchers are seeking large families with two or more living relatives with late-onset AD. Families interested in participating in this study can contact the National Cell Repository for Alzheimer’s Disease at 1-800-526-2839. Information may also be requested through their website, http://ncrad.iu.edu.