A person whose parent or a sibling had the disease has a risk factor of developing late onset Alzheimer’s Disease (AD). But this is only one of many risk factors. Research on the genetics of AD has produced a mixed bag of results, although scientists have discovered at least 20 different genes that may play a role in 80 percent of AD cases. They have also discovered genes that “protect” against the disease. It’s known that a person who inherits a gene variant called E4 is 25 percent more likely to develop late onset AD than a person without this gene. And if a person inherits the variant from both the father and mother, he or she has four times the normal risk for AD. However, some people have either one E4 gene, or have a double dose of E4, and never develop AD. It may be the genes that protect against AD play a significant role in such cases. The bottom line is that there is too much uncertainty for a person to seek genetic tests that may or may not show risk factors. There is only one study that shows certain genetic mutations guarantee early-onset AD. In that study, every member of a family had such a strong genetic risk that all developed AD by a median age of 49.
There are things one can do to minimize chances of having AD: Eat a healthy diet low in fat, sugars, and processed food, and rich in fish, poultry, nuts, and fresh fruits and vegetables; manage medical conditions; exercise regularly; and get at least seven or eight hours of sleep each night. (Mind, Mood, and Memory, 2016, June issue, a publication of Massachusetts General Hospital; alzheimers.org.uk)