Several genes are directly associated with some types of Alzheimer’s disease, which may increase the risk of inheritance. That said, hereditary Alzheimer’s is very rare.

Alzheimer’s disease (AD) is a neurodegenerative condition characterized by progressive cognitive decline and memory loss. AD affects around 6 million people in the United States.

The exact cause of AD isn’t known, but researchers believe it occurs when abnormal deposits of two proteins called amyloid and tau build up in the brain:

  • Amyloid: Amyloid buildup may lead to the formation of plaques that could interrupt the function of certain brain cells.
  • Tau: Tau may build up inside neurons — the messengers in your brain — and cause neurofibrillary tangles that may disrupt the communication of neurons in your brain.

Over time, the effects of these protein buildups may cause neurons to die, leading to brain damage.

Research suggests that genetics may play a key role in the development of AD and contribute to other pathways that may cause AD.

Keep reading to learn more about how genes are related to the development of AD, as well as other possible causes.

AD is more common in people ages 65 years and older, which is known as late-onset AD (LOAD).

However, research suggests that genetics may play a bigger hereditary role in early-onset AD (EOAD), which affects people younger than 65 years old.

EOAD, sometimes referred to as familial AD (FAD), is rare, but research is mixed on its prevalence and the role of genetic inheritance.

The National Institute of Aging and a 2021 review suggest that 1 in 10 people may receive a diagnosis of EOAD, but only 10% to 15% of these people show signs of genetic inheritance.

On the other hand, a 2023 review found that up to 5% of AD cases are inherited, while the Alzheimer’s Association suggests that less than 1% of AD is inherited.

Nevertheless, researchers and healthcare organizations agree that LOAD is much more common, accounting for 9 out of 10 cases of AD. However, genetics play a smaller role than they do in EOAD.

Having a family member with AD may increase your risk of developing AD, especially if more than one family member has AD.

More than 80 genes are associated with AD, and researchers continue to find more.

Researchers classify genes into two categories based on their role in disease development:

  • Deterministic genes: These may directly cause AD.
  • Risk genes: These may increase the risk of developing AD later in life.

Genetics and familial AD (EOAD)

Mutations in three deterministic genes may cause EOAD if one copy of the gene is inherited from either parent:

  • amyloid precursor protein (APP)
  • presenilin 1 (PSEN1)
  • presenilin 2 (PSEN2)

Variations in these genes contribute to the development of amyloid plaques and neurofibrillary tangles in the brain, which may kill neurons and lead to the progression of AD symptoms.

A 2021 review suggests these genes are also involved in other pathways that may contribute to AD, including:

Genetics and LOAD

The role of genetics in LOAD is less certain than in EOAD, but researchers have identified over 100 risk genes that may contribute to LOAD.

The apolipoprotein E-4 allele (APOE4) risk gene has the strongest association with LOAD. Up to 65% of people with AD have APOE4, according to the Alzheimer’s Association.

Down syndrome

Having Down syndrome may also increase your risk of inheriting AD.

This may be because people with Down syndrome have an extra copy of chromosome 21. This means they also have an extra copy of the APP gene, which is associated with the development of amyloid plaques and AD.

According to the Alzheimer’s Association, many people with Down syndrome have a significant buildup of amyloid plaques and neurofibrillary tangles by 40 years. An estimated 9 in 10 people with Down syndrome will develop dementia, of which AD is the most common type.

Other genes associated with AD

Researchers have identified several other genes that may contribute to AD development. Some of these include:

  • SORL1
  • ABCA7
  • TREM2
  • BIN1
  • UNC5C
  • AKAP9
  • NOTCH3
  • 12A
  • rRNA
  • CLU
  • PLCG2
  • ABI3
  • APOE

Is Alzheimer’s inherited from the mother or father?

Alzheimer’s disease may be inherited from either parent, regardless of sex assigned at birth.

According to the Alzheimer’s Association, each person inherits a copy of the APOE gene from both parents.

However, if you inherit a copy of the APOE 4 allele gene, your risk of AD increases. This could be inherited from either parent.

Genetic testing for AD may help detect whether you’ve inherited deterministic or risk genes associated with AD. It could help provide a diagnosis of AD or determine your risk for developing the condition later in life.

According to the National Institute of Aging, a healthcare professional may recommend genetic testing for genes APP, PSEN1, and PSEN2 if someone in your family has AD and you experience symptoms of EOAD.

Genetic testing for APOE4 is mostly used in a research or clinical setting to help identify whether you have the gene or not. This can’t provide a diagnosis of AD, but it may suggest an increased risk for LOAD, which may prompt you to take preventive measures.

Learn more about genetic testing for AD.

Researchers have identified environmental, lifestyle, and genetic risk factors associated with AD, including:

  • being age 65 years and older
  • being assigned female at birth
  • traumatic brain injuries (TBIs)
  • chronic health conditions, such as diabetes, obesity, stroke, and heart disease
  • depression and chronic stress
  • lifestyle factors, such as smoking, not exercising regularly, and not eating a balanced diet

Learn more about the causes and risk factors of AD.

AD is a neurodegenerative condition caused by a mixture of genetic, environmental, and lifestyle factors.

Researchers suggest that familial AD, also known as early-onset AD, may be caused by inheriting APP, PSEN1, and PSEN2 genes. Later-onset AD is associated with the APOE4 gene.

If someone in your family has AD, consider speaking with a healthcare professional about genetic testing. They could help determine your risk for developing AD later in life.