While family history is not the only determining factor when it comes to the development of Alzheimer’s and other dementia disorders, it does play a role. If you have a first-degree relative (a parent or full sibling) with Alzheimer’s, you are at a higher risk for developing the disease.
Researchers aren’t certain to what extent genetics, environmental factors, or a combination of the two determine a person’s risk, but progress is being made as scientists are now able to identify the genes that cause hereditary Alzheimer’s.
There are two types of genes that influence whether a person develops any disease: risk genes and deterministic genes.
Risk genes increase the likelihood of developing a disease but do not guarantee it will happen. The gene with strongest impact for Alzheimer’s risk is APOE-e4. Researchers estimate that 40-65% of people diagnosed with Alzheimer’s have this gene. There are two other common forms of the APOE gene: APOE-e2 and APOE-e3. We all inherit a copy of some form of APOE from each parent. Those who inherit one copy of APOE-e4 from either parent have an increased chance of developing the disease. Those who inherit one copy from BOTH parents have an even higher risk. Approximately 20-30% of people in the U.S. have one or two copies of APOE-e4, and approximately 2% have two copies.
Deterministic Genes directly cause a disease. These genes account for 1% or less of all Alzheimer’s cases worldwide, and they are more likely to cause early-onset Alzheimer’s (from the early 40s to mid-50s). While these genes are extremely rare, they’re critical to our understanding of how Alzheimer’s affects the brain. These genes affect the processing or production of beta-amyloid, a prime suspect in the decline and death of brain cells. The first drug approved by the FDA to treat Alzheimer’s (Aducanumab or “Aduhelm”) works by removing amyloid from the brain in an effort to reduce cognitive decline.
Genetic testing is available for both APOE-e4 and the rare deterministic genes that cause Alzheimer’s. These tests are not recommended for the general population, but if you’re considering getting tested due to family history, the Alzheimer’s Association recommends genetic counseling from the National Society of Genetic Counselors before testing and after receiving the results. Visit their website to learn more.