Some research suggests that a person is at increased risk for developing Alzheimer’s disease if a relative has the disorder. However, the causes of the condition are unclear.

Alzheimer’s disease is a chronic, progressive condition that impairs memory, thinking, and movement.

Current research suggests that multiple factors may contribute to the development of Alzheimer’s, including genetics.

This article assesses the potential links between genetics and Alzheimer’s disease.

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Scientists describe genetic risks for Alzheimer’s in terms of two factors: risk genes and deterministic genes.

When a person has risk genes, it means they have an increased chance of developing a disease. Deterministic genes may directly cause a disease to develop.

Scientists have found several risk and deterministic genes for Alzheimer’s.

Risk genes

Several genes present a risk for Alzheimer’s. The gene with the most significant connection to Alzheimer’s risk is the apolipoprotein E-E4 gene (APOE-e4).

According to the Alzheimer’s Association, an estimated 15–25% of people with this gene may go on to have Alzheimer’s disease. A person who inherits the APOE-e4 gene from both parents also has a higher risk of developing Alzheimer’s disease than someone who inherits the gene from only one.

Having the gene may also mean that a person displays symptoms at an earlier age and receives a diagnosis earlier.

While every person inherits an APOE gene of some form, the APOE-e3 and APOE-e2 genes have no association with Alzheimer’s disease. APOE-e2 might even provide protective effects on the brain against the disease.

The trisomy 21 gene can also significantly increase a person’s risk of Alzheimer’s.

Deterministic genes

Researchers have identified three specific deterministic genes that may cause Alzheimer’s disease:

  • amyloid precursor protein (APP)
  • presenilin-1 (PS-1)
  • presenilin-2 (PS-2)

These genes are responsible for an excessive buildup of amyloid-beta peptides. This is a toxic protein that clumps together in the brain. This buildup causes nerve cell damage and death, characteristic of Alzheimer’s disease. These genes are known as “dominant genes,” which means that if either parent has the condition, they can pass on the gene to their children, and they will develop the disease.

These gene mutations account for 60–70% of all familial early onset Alzheimer’s disorder cases and 5–10% of early onset dementia overall. Alzheimer’s caused by deterministic genes typically occurs before the age of 65 years. It can sometimes develop in people who are in their 40s and 50s.

However, not all people with early onset Alzheimer’s have these genes.

Effect of genes in other types of dementia

Some types of dementia have links to other genetic malformations.

Huntington’s disease, for example, alters chromosome 4, which can lead to progressive dementia. Huntington’s disease is a dominant genetic condition.

Dementia with Lewy bodies or Parkinson’s dementia may also have a genetic component. For example, Parkinson’s has known associations with several genes, including SNCA, PARK7, and PRKN. However, as with all forms of dementia, the cause of these conditions is typically multifactorial.

Researchers have identified several risk factors for Alzheimer’s disease.

These include:

  • Age: The most significant risk factor for Alzheimer’s disease is age.
  • Family history: Having a close relative with Alzheimer’s disease increases the risk of developing it.
  • Head trauma: People with previous instances of severe head trauma may be at higher risk of developing Alzheimer’s disease.
  • Heart health: Health issues in the heart or blood vessels may increase the chance of developing Alzheimer’s disease. Examples include high blood pressure, stroke, and diabetes.

Alzheimer’s disease usually involves a gradual loss of memory and brain function.

Early symptoms may include periods of forgetfulness or memory loss. Over time, a person may experience confusion or disorientation in familiar settings, including at home. As a result, they may need more assistance with daily living, such as brushing their teeth, getting dressed, and cutting food.

They may also experience agitation, restlessness, personality withdrawals, and speech issues.

The survival rate for a person with Alzheimer’s disease is usually 8–10 years after the first appearance of symptoms.

Learn more about the stages of Alzheimer’s disease and their outlook.

Seeking medical assistance for a person who demonstrates these symptoms is vital, even though the discussion might be difficult. A doctor can rule out other diseases that might cause Alzheimer’s disease.

Before an appointment, family members should make a list of any medications the person with symptoms is currently taking. The doctor can review the list and ensure symptoms are not side effects of current medications.

Keep a journal of noticeable symptoms as they develop over time to help a doctor establish potential patterns.

Sometimes, a doctor may recommend genetic testing when people show early Alzheimer’s symptoms, which may dictate possible treatments and assist in future family planning.

However, the results of genetic testing can negatively affect a person’s emotional well-being should it provide an unwanted outcome. Working with a doctor or counselor during and after the genetic testing process can help people better understand the results and implications.

Alzheimer’s disease has links to several genes. Some, such as the APOE-e4 gene, increase the risk of developing the disease but do not always lead to an Alzheimer’s diagnosis.

Others, such as the APP gene, directly cause the disease to develop. However, this is a rare type known as familial Alzheimer’s that occurs in 5–10% of people with early onset Alzheimer’s disease.