Is Alzheimer's Disease Genetic?

Genes influence your Alzheimer's disease risk, but just because dementia runs in your family doesn't mean you're destined to develop it. Here’s what you should know.

Every three seconds, someone in the world learns they have Alzheimer's disease. When one of those people is your grandparent, parent, aunt, or uncle, it's normal to worry not only about their future but also your own.

Genes do influence your Alzheimer's disease risk, but just because dementia runs in your family doesn't mean you're destined to develop it. More important is the specific type of gene(s) you carry, the closeness of the family connection, and how many of your relatives Alzheimer's affects.

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Do you have a strong family history of Alzheimer’s?

Your family tree can give you some insight into your Alzheimer's risk. Having one first-degree relative (a parent, child, or sibling) with Alzheimer's makes you nearly twice as likely to develop the disease yourself. If two of your first-degree relatives have Alzheimer's, your risk goes up fourfold.

Having second-degree relatives (grandparents, aunts, uncles) with Alzheimer's doesn't increase your risk quite as much. If Alzheimer's has affected several people in your family, however, it could affect your likelihood of developing this disease.

The genetic roots of Alzheimer's

How Alzheimer's passes down through families depends on two categories of genes.

Risk genes make you more likely to get Alzheimer's disease. One of these is the apolipoprotein E (APOE) gene. It comes in three main versions, APOE-e2, APOE-e3, and APOE-e4. By far the most common of these is APOE-e4.

About 1 in 4 people in the United States carry one copy of the APOE-e4 gene, which codes for a protein that helps move cholesterol and other fats through the bloodstream. Exactly why APOE-e4 increases Alzheimer's risk is unclear, but it may have something to do with a problem in the brain's ability to process fats.

Having one copy of the APOE-e4 gene more than doubles your odds of developing Alzheimer's after age 65. Having two copies, which around 2 percent of us do, increases your risk up to tenfold. But even if you do have this gene, developing Alzheimer's is not a given. Other factors, including your environment, also affect your risk.

Deterministic genes directly cause Alzheimer's. It takes only one of these three genes, inherited from your mother or father, for you to develop the disease:

• Presenilin 1 (PS1)
• Presenilin 2
• Amyloid precursor protein (APP)

These genes cause the familial form of Alzheimer's, which develops early in life. Symptoms can appear as early as your 30s or 40s. Fortunately, this form of dementia is very rare. Single-gene mutations account for 1 percent or fewer of all Alzheimer's cases, according to the Alzheimer's Association.

Should you get tested for Alzheimer’s genes?

Blood tests are available to detect APOE-e4 and the three less common gene mutations that cause early-onset Alzheimer's. But just because these tests exist doesn't mean you necessarily need them.

The Alzheimer's Association doesn't recommend testing everyone. If you have multiple family members with the disease or early-onset Alzheimer’s runs in your family, it might be worth seeing a genetic counselor. You can find one through the National Society of Genetic Counselors.

The counselor will review your family and personal medical history and help you decide whether testing is in your best interest. While the results can be helpful for planning a family and thinking about possible treatments, they can also carry a heavy emotional burden. They may also have implications for your future employment and life insurance prospects.

What you can do

By far the biggest risk for Alzheimer's disease is age. More than one in three people will have the condition by the time they reach their 80s. Age and genes aren't modifiable risks. You can't reverse the clock or change your parentage.

Other risks are more within your control. The Lancet Commission on dementia prevention estimates that 12 risk factors account for around 40 percent of all dementias. Changing these risks with simple lifestyle modifications might help you potentially delay, or even prevent Alzheimer's:

1. Keep your systolic blood pressure (the top number) at 130 millimeters of mercury (mm Hg) or less.
2. Reduce your exposure to secondhand smoke and pollution.
3. Abstain from alcohol or drink it in moderation.
4. Avoid smoking. If you already smoke, get help to quit.
5. Prevent head injuries.
6. Exercise regularly to lose weight and prevent diabetes if you are overweight.
7. Get treated for insomnia or other sleep disturbances that are keeping you awake.

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