Is Alzheimer’s disease genetic?
When it comes to evaluating risk for developing a disease, there are factors that we can control and others with which we are simply born. When a family member is diagnosed with Alzheimer’s, many people become worried they will also inevitably fall victim to the disease because of their genes. Fortunately, our genes have a much smaller role to play in this disease than is widely assumed. Genetic factors only play a strong role in less than 5% of all Alzheimer’s cases where the inheritance among family members is extremely high. These families suffer from “Familial” Alzheimer’s disease and you likely already know if you are in one of these families because there are only a few hundred in the world.
For the rest of us, we are at risk for what’s called late-onset or “sporadic” Alzheimer’s disease, where the greatest risk factor is increasing age. Now this does not mean that genes and family history have absolutely no role in sporadic Alzheimer’s, it’s just that their contribution is much smaller. The most commonly studied risk gene associated with Alzheimer’s disease is called apolipoprotein E-e4 (APOE-e4). Individuals who inherit a copy of APOE-e4 — you can have zero, one, or two copies of any gene – are at an increased risk for developing Alzheimer’s, but this does not necessarily mean they will develop it. An individual can inherit two copies of APOE-e4 and never develop Alzheimer’s because the gene is not deterministic; it is only a risk factor. In the U.S., the estimated lifetime risk of developing Alzheimer’s for a 65-year-old man is about 9%, while it is about 17% for a woman of that same age (the risk is higher because women live longer). For individuals with an affected first-degree relative (sibling or parent), the risk for developing the disease is slightly higher and it’s also slightly increased for those with an affected second-degree relative (e.g., grandparents). Beyond those relationships there is not a significantly increased risk. Thus, as is the case with many other late-onset disorders, an individual’s specific lifetime risk for Alzheimer’s is determined by a combination of genetic and environmental factors, not a single determinant or gene. What this means is that even a woman whose father has Alzheimer’s has a greater than 80% chance of never developing the disease. While those odds may not sound great to many, they are very far from a predestined fate of Alzheimer’s.
I read blueberries will prevent me from getting Alzheimer’s disease, is that true?
A popular misconception about Alzheimer’s has to do with a part of our lives we can control — our diets. You might have heard that eating certain berries or fish oils will prevent someone from developing the disease. While it’s true many types of berries contain antioxidants, which are generally beneficial to your health, they have not been shown to prevent Alzheimer’s. Similarly, fish contain a fatty acid called docosahexaenoic acid (DHA) that has been shown in some studies to improve memory and protect against age-related ailments. This has spurred people to start taking fish oil pills and other related supplements in an effort to ward off Alzheimer’s. However, other studies and clinical trials have been unable to confirm the beneficial effects of fish oils, showing no appreciable effect in large samples of people followed over 18 months. Importantly, eating more berries or taking fish oil supplements in moderation has also not been shown to be harmful to anyone, so the only effect that these dietary changes may have are on your wallet.
Whether it’s a friend giving you advice or a story you read in the newspaper, it is important to factcheck information about Alzheimer’s disease. Myths such as, “genes are the most important factor” or “eating berries will protect you,” are easily dismantled with a little bit of research.
Eric Chang, Ph.D. received his doctorate in Neural Science from New York University where he studied the neurophysiological mechanisms of Alzheimer’s disease. He is currently an Assistant Investigator at the Feinstein Institute for Medical Research, the biomedical research branch of the North Shore-LIJ Health System. Eric has also been an active member of the NYC Chapter Speaker’s Bureau since 2005. He can be reached at: firstname.lastname@example.org.