Yes, there are genes linked to Alzheimer’s disease, but they work in two very different ways. A small number of gene mutations directly cause Alzheimer’s and virtually guarantee the disease will develop, usually before age 65. Far more common are risk genes that increase your chances of developing Alzheimer’s without making it inevitable. Fewer than 1% of all Alzheimer’s cases are caused by the deterministic mutations, while risk genes play a contributing role in a much larger share of cases.
The Risk Gene Most People Carry or Don’t: APOE
The gene with the strongest influence on typical, late-onset Alzheimer’s is called APOE. Everyone inherits two copies of this gene (one from each parent), and it comes in three common variants: e2, e3, and e4. The e3 variant is the most common and carries a neutral level of risk. The e2 variant is associated with lower risk. The e4 variant is the one tied to Alzheimer’s.
Having one copy of the e4 variant doubles or triples your risk of developing Alzheimer’s. Having two copies (one from each parent) makes you 8 to 12 times more likely to develop it. A 2024 study published in Nature Medicine went further, proposing that people who carry two copies of APOE e4 should be considered a distinct genetic form of Alzheimer’s, not just a risk category. Researchers found that virtually all of these individuals developed Alzheimer’s-related brain changes by age 65, sharing key characteristics with other genetically determined forms of the disease.
Still, carrying one copy of e4 is not a diagnosis. Many people with the variant never develop Alzheimer’s, and many people without it do. Roughly 20 to 25% of the population carries at least one copy of e4.
Ancestry Changes How the Gene Behaves
The risk that APOE e4 carries is not the same across all populations. People of European ancestry who inherit two copies face roughly 10 times the risk compared to people with other variants. But carriers of African ancestry have a notably lower risk from the same gene, while carriers of Asian ancestry have a higher risk than Europeans.
This isn’t simply about lifestyle or environmental differences. Research from the National Institute on Aging found that it’s the genetic ancestry surrounding the APOE gene that determines the risk, not the gene itself. If a person with mixed European and African ancestry inherited their e4 copy from their African ancestor, they carried the African level of risk. If it came from their European ancestor, they carried the European level of risk. The explanation appears partly biological: brain cells in people with European genetic ancestry around the APOE e4 gene produced almost 40% more of the APOE protein than cells from people with African ancestry around the same gene. They also had more of a type of inflammatory brain cell thought to contribute to the degenerative process.
Genes That Directly Cause Alzheimer’s
A separate category of genes doesn’t just raise risk. It causes the disease outright. Mutations in three genes (APP, PSEN1, and PSEN2) are responsible for most cases of inherited early-onset Alzheimer’s, which typically appears between a person’s 30s and mid-60s. If you inherit one of these mutations from either parent, you will almost certainly develop the disease.
These mutations are rare. About 11% of people with young-onset Alzheimer’s carry one of these causal mutations, but among all people with Alzheimer’s (including the much larger group diagnosed after 65), fewer than 1% carry them. Families affected by these mutations often see the disease appear in multiple generations, at roughly the same age each time.
Other Genes That Contribute Smaller Amounts of Risk
Beyond APOE, researchers have identified dozens of other gene variants that each nudge Alzheimer’s risk up by a small amount. Three of the more significant ones are TREM2, SORL1, and ABCA7. Rare damaging variants in these genes were each found to account for about 1% to 1.5% of the inherited component of early-onset Alzheimer’s risk, compared to about 9% for APOE e4. People carrying harmful variants in TREM2 face roughly six times the risk, while SORL1 variants roughly triple it and ABCA7 variants roughly double it.
These genes are involved in different biological processes, from immune response in the brain to clearing out damaged proteins. Individually, their effect is smaller than APOE e4, but collectively they help explain why Alzheimer’s risk varies so much between people, even among those who share the same APOE status.
Genes Are Only Part of the Picture
Even with a strong genetic risk profile, Alzheimer’s is not purely a genetic disease for the vast majority of people. The strongest known risk factor is age itself, and lifestyle factors like physical activity, diet, sleep, cardiovascular health, and social engagement all influence whether and when symptoms appear.
There is also growing evidence that lifestyle factors can change how Alzheimer’s-related genes behave. The body uses chemical tags on DNA to turn genes up or down, a process called epigenetics. Nutrient levels, particularly B vitamins and folate, appear to influence these chemical tags on genes related to brain health. As people age, levels of key molecules involved in this process tend to decline, which may partially explain why Alzheimer’s risk climbs so steeply with age.
Genetic testing for APOE status is commercially available, but knowing your result doesn’t tell you whether you will or won’t develop Alzheimer’s. It tells you something about your relative risk compared to the general population, which some people find useful for planning and motivation, and others find anxiety-inducing without a clear path to prevention. If you have a strong family history of Alzheimer’s, particularly cases appearing before age 65, genetic counseling can help determine whether testing for the rarer causal mutations is appropriate.