Alzheimer’s disease is a condition that affects millions of families, and as people get older, many wonder, “Will it happen to me, too?” It’s a scary question, especially for children or grandchildren who have watched the disease unfold up close. Some families see Alzheimer’s appear generation after generation, while others never face it at all. So, how much of Alzheimer’s risk comes from the genes we inherit?

Scientists have made important progress in understanding how Alzheimer’s develops, but the answer to whether it’s inherited isn’t straightforward. Some genetic mutations (variations) passed down from our biological parents can raise or lower a person’s risk. But not everyone with these changes will get Alzheimer’s — and not everyone who gets the disease has a family history.

You can think of our genes like an instruction manual for the body. Some variations are like small typos that slightly increase the risk of problems. Others are more serious errors that almost guarantee a disease will occur. Genetic testing can now uncover some of this information, but deciding whether to be tested brings its own challenges.

In this article, we’ll break down what scientists have learned about the genetics of Alzheimer’s disease — and what it means for you and your family.

Overview of Familial Alzheimer’s Disease

In some families, Alzheimer’s seems to appear in every generation. This happens in a rare form called familial Alzheimer’s disease (FAD). FAD is inherited, meaning it’s passed down from a biological parent to their child. It’s different from the more common late-onset Alzheimer’s, which usually affects older adults. FAD accounts for fewer than 1 percent of all Alzheimer’s cases.

Unlike typical Alzheimer’s, which usually appears in people over age 65, FAD often starts much earlier. Most people with FAD develop symptoms in their 40s or 50s — and in some families, it can begin as early as the 30s. The early onset can be especially challenging, affecting people in the prime of their careers, parenting, and personal lives. The first signs usually look like typical Alzheimer’s — progressive memory loss that goes beyond everyday forgetfulness. Often, family members notice the changes before the person affected does. Over time, problems with planning, judgment, and other thinking skills also appear.

FAD is also called autosomal dominant Alzheimer’s disease (ADAD). This term describes how the condition is inherited. If one biological parent carries the gene mutation, each child has a 50 percent chance of inheriting it. The condition affects people of any sex and doesn’t skip generations. Families with FAD usually have several relatives — parents, grandparents, aunts, uncles, or cousins — who developed Alzheimer’s symptoms around the same age.

Genes Involved in Familial Alzheimer’s Disease

Scientists have identified three specific genes that cause familial Alzheimer’s disease. These genes contain instructions for making proteins that are important for brain cell function. When one of these genes has a mutation, it’s like a faulty instruction that leads to a harmful buildup of beta-amyloid — a sticky protein that clumps together in the brain. This buildup damages neurons (the nerve cells in the brain) and leads to the symptoms of Alzheimer’s.

The three genes linked to familial Alzheimer’s are:

• Amyloid precursor protein (APP) — This gene makes a protein that can be broken down into smaller pieces, including beta-amyloid, which can build up and form plaques in the brain.
• Presenilin 1 (PSEN1) — This gene is the most common gene linked to FAD. Carriers of a PSEN1 mutation almost always develop the disease, sometimes as early as their 30s.
• Presenilin 2 (PSEN2) — Mutations in this gene are less common but still strongly linked to FAD. Carriers face a very high likelihood of developing the disease.

These are called deterministic gene mutations because inheriting one almost always means a person will develop Alzheimer’s — usually before age 65, and often much earlier.

APOE and Risk of Late-Onset Alzheimer’s

While familial Alzheimer’s disease is very rare, the much more common type is late-onset Alzheimer’s disease, which usually develops after age 65. In this form of the disease, certain genes can influence a person’s risk, but they don’t fully determine who will or won’t get Alzheimer’s.

The most studied gene linked to late-onset Alzheimer’s is called APOE, short for apolipoprotein E. The APOE gene helps carry cholesterol in the blood and also plays a role in brain health.

APOE comes in several versions, known as alleles:

• APOE2
• APOE3
• APOE4

Everyone inherits two copies of the APOE gene, one from each biological parent.

The APOE4 allele is also known as a risk gene. This means it can increase the chance of Alzheimer’s, but it doesn’t guarantee that it will happen. In contrast, the APP, PSEN1, and PSEN2 mutations found in familial Alzheimer’s are called deterministic genes: Inheriting one of those almost always leads to the disease.

Carrying one copy of APOE4 raises a person’s risk for Alzheimer’s, and carrying two copies raises it even higher. About 2 percent of the general population in the United States has two copies of APOE4. People with two copies have about a 60 percent chance of developing Alzheimer’s by the age of 85.

The Roles of Genes vs. Environment

In FAD, mutations in genes like APP, PSEN1, or PSEN2 are the main drivers. These mutations are so strong that they almost always lead to Alzheimer’s. Still, researchers have found that even within the same family, symptoms don’t always begin at the same age.

For example, in some families with PSEN1 mutations, the age of onset can differ by a decade or more between relatives. This suggests that other factors — including health and lifestyle — may influence when symptoms start and how quickly they progress.

These influencing factors can include:

• Overall health
• Other medical conditions
• Lifestyle choices, such as physical activity and diet

For other types of Alzheimer’s — particularly late-onset — environmental (nongenetic) risk factors appear to play an even greater role. Some factors linked to increased risk include:

• Hypertension (high blood pressure)
• Type 2 diabetes
• Past head injuries

At the same time, protective factors may help delay the onset of symptoms, including:

• Eating a balanced diet
• Staying socially connected
• Keeping the brain active through learning or mentally engaging activities

Genetic Testing for Alzheimer’s

If FAD runs in your family, you may be thinking about genetic testing to better understand your personal genetic risk. A good first step is to talk with your doctor, who can refer you to a genetics clinic. There, you’ll meet with a genetic counselor — a specially trained healthcare professional who can walk you through your options.

What Does a Genetic Counselor Do?

Genetic counselors help you understand how genetic testing works, what the results might mean, and what steps you can take next. They’ll also talk through the emotional, medical, and practical sides of knowing your genetic risk. The goal is to give individuals and their families the information they need to make informed choices. You may want to include close relatives who share similar risk in these discussions as well.

How Is Genetic Testing Done?

Testing is typically done using a blood sample or saliva. There are two main types of genetic testing:

• Diagnostic testing is used when someone already has symptoms of Alzheimer’s at a young age and has a strong family history.
• Predictive testing can show whether someone has inherited a specific gene mutation before any symptoms appear.

Planning for the Future

For families concerned about passing on a genetic mutation, preimplantation genetic diagnosis (PGD) may be an option. This process combines in vitro fertilization (IVF) with genetic testing of embryos, allowing parents to choose embryos that do not carry the specific gene mutation linked to FAD. PGD is a complex, time-intensive process, but for some families, it provides a path to have children without passing on a deterministic gene.

What Genetic Testing Means for Families

For families affected by FAD, knowing that a gene mutation almost always leads to Alzheimer’s can bring up overwhelming emotions, including fear, sadness, and sometimes guilt. Genetic testing can offer insights, but it also has limits. A positive result confirms elevated risk but can’t predict when symptoms will start or how the disease will progress. A negative result can offer relief, but may also lead to survivor’s guilt if other relatives test positive.

Deciding whether to undergo genetic testing is a deeply personal choice. Some people want information to help them plan ahead, while others prefer not to know. Both choices are valid and deserve understanding and respect. Because the results can affect not just one person but the entire family, it’s important to approach testing with care, honesty, and support.

This is where genetic counseling becomes especially valuable. Counselors help families work through complex emotions, weigh difficult choices, and understand how test results could influence future plans. These conversations often include practical considerations like long-term care planning, insurance options, and decisions about joining clinical trials (studies of potential new treatments).

Talk With Others Who Understand

On myALZteam, people share their experiences with Alzheimer’s disease, get advice, and find support from others who understand.

Do you have a family history of FAD? Let others know in the comments below.