Alzheimer’s is the most common form of dementia in older adults—and the risk increases by about 30%. A family history is not necessary for an individual to develop Alzheimer’s.
However, studies show that those who have a parent or sibling with Alzheimer’s are more likely to develop the disease than those who do not have a first-degree relative with Alzheimer’s. Those who have more than one first-degree relative with Alzheimer’s are at an even higher risk. When diseases like Alzheimer’s and other dementia tend to run in families, either genetics, environmental factors — or both — may play a role.
Certain genes increase the risk of getting Alzheimer’s disease.
Genes control how every cell in the body works. Some genes decide basic traits, such as the color of the eyes and hair. Other genes can increase the risk of getting certain diseases, including Alzheimer’s disease.
Below are two categories of genes that influence whether a person can develop a disorder:
- Risk genes and
- Deterministic genes.
Researchers have identified hereditary Alzheimer’s genes in both these categories…
Risk genes:
Risk genes increase the chances of developing a disease but do not guarantee it will happen. Researchers have found several genes that increase the risk of Alzheimer’s. Apolipoprotein E (APOE-e4) is the first risk gene identified and remains the gene with the strongest impact on the risk. About 65% of people diagnosed with Alzheimer’s have the APOE-e4 gene.
Those who inherit one copy of APOE-e4 from their mother or father have an increased risk of developing Alzheimer’s. Those who inherit two copies from their mother and father have an even higher risk, but not a certainty. In addition to raising risk, APOE-e4 may tend to make symptoms appear at a younger age than usual.
Genetic tests are available for both APOE-e4 and the rare genes that directly cause Alzheimer’s. Testing for APOE-e4 is sometimes included as a part of research studies.
Deterministic genes:
Deterministic genes directly cause a disease, guaranteeing that anyone who inherits one will develop a disorder. These genes, which are estimated to account for 1% or less of Alzheimer’s cases, cause familial early-onset forms in which symptoms usually develop between a person’s early 40s and mid-50s. The vast majority of individuals with Alzheimer’s have late-onset disease, occurring at age 65 or later.
Although the hereditary genes that cause “familial Alzheimer’s” are rare, their discovery has provided important clues that help our understanding of Alzheimer’s. All of these genes affect the processing or production of beta-amyloid, the protein fragment that is the main component of plaques. Beta-amyloid is a prime suspect in the decline and death of brain cells.
The Alzheimer’s Association cautions against routine genetic testing for Alzheimer’s disease risk until an individual has received proper counseling and understands the information necessary to make an informed decision, including the social and economic factors that could be impacted by having this genetic information.
However, there may be specific instances when an individual living with Alzheimer’s should discuss genetic testing with their physician, as the results could impact a treatment decision. Individuals should seek the services of a genetic counselor before and after deciding to undergo testing.
