inherited

Is dementia hereditary? In most cases, dementia is not inherited in a simple parent-to-child pattern. Having a parent or sibling with dementia can increase your risk, but it does not mean that you will develop dementia yourself.

There are, however, some important exceptions. Certain rare forms of Alzheimer’s disease, frontotemporal dementia and vascular dementia can be caused by inherited genetic changes that run strongly through families.

The relationship between dementia and genetics can therefore be confusing. The important distinction is between genes that increase risk and rare genes that directly cause disease.

Is Dementia Hereditary? The Short Answer

For most people, the answer is not directly.

According to the National Institute on Aging, most cases of Alzheimer’s disease do not have a single genetic cause. Instead, multiple genes may interact with age, health, lifestyle and environmental factors.

A family history of dementia can still matter. If a parent or sibling has Alzheimer’s disease, your risk is higher than that of someone without an affected first-degree relative. Having several close relatives with dementia can increase concern further.

But increased risk is very different from certainty.

Many people with a strong family history never develop dementia, while many people who develop dementia have no known family history at all.

Does Dementia Run in Families?

Dementia can appear to run in families for several reasons.

Family members share genes, but they may also share:

• Eating patterns
• Physical activity levels
• Smoking habits
• Blood pressure risk
• Diabetes risk
• Cardiovascular risk
• Environmental exposures

For this reason, several relatives developing dementia does not automatically mean there is one inherited dementia gene being passed through the family.

Age is also extremely important. Dementia becomes much more common as people get older. Several family members developing dementia in their 80s, for example, does not necessarily suggest the same type of inherited disorder as several relatives developing dementia in their 40s or 50s.

Risk Genes vs. Disease-Causing Genes

Understanding the difference between risk genes and disease-causing genetic variants makes the genetics of dementia much easier to understand.

Risk Genes

A risk gene changes the likelihood that someone will develop a condition.

It does not guarantee that the person will develop it.

The best-known example in Alzheimer’s disease is APOE.

The APOE Gene

Everyone inherits one copy of the APOE gene from each biological parent.

There are several common forms, or alleles, including:

• APOE ε2 – may provide some protection against Alzheimer’s disease.
• APOE ε3 – the most common form and generally considered neutral for Alzheimer’s risk.
• APOE ε4 – associated with an increased risk of Alzheimer’s disease and, in some populations, an earlier age of onset.

Having one APOE ε4 allele increases risk. Having two copies generally increases risk further.

However, APOE ε4 does not mean that Alzheimer’s disease is inevitable. Some people with APOE ε4 never develop Alzheimer’s, while many people without APOE ε4 do.

The National Institute on Aging’s Alzheimer’s genetics guide provides more information about APOE and other genetic variants.

Disease-Causing Genetic Variants

There are also rare genetic changes that can directly cause particular forms of dementia.

These are much less common but can create a very strong pattern of dementia across generations.

Is Alzheimer’s Disease Hereditary?

Most Alzheimer’s disease is not directly inherited.

The most common form is late-onset Alzheimer’s disease, which usually develops after age 65. Genetics can influence risk, but there is usually no single gene that determines whether a person will develop the disease.

The Alzheimer’s Association explains that having a parent or sibling with Alzheimer’s increases risk, particularly if several first-degree relatives have been affected.

Rare Familial Alzheimer’s Disease

A very small proportion of Alzheimer’s cases are caused by inherited changes in one of three genes:

• APP – amyloid precursor protein
• PSEN1 – presenilin 1
• PSEN2 – presenilin 2

These rare genetic variants can cause autosomal dominant Alzheimer’s disease.

If a biological parent carries one of these disease-causing variants, each child has a 50% chance of inheriting that altered gene.

When inherited, these variants are strongly associated with Alzheimer’s developing before age 65 and sometimes much earlier.

The National Institute on Aging estimates that fewer than 10% of people with Alzheimer’s have younger-onset disease, and only a portion of those cases are explained by APP, PSEN1 or PSEN2 variants.

Down Syndrome and Alzheimer’s Genetics

There is also an important genetic relationship between Down syndrome and Alzheimer’s disease.

People with Down syndrome have an extra copy of chromosome 21. This chromosome contains the APP gene involved in amyloid production.

As a result, people with Down syndrome have a much higher risk of developing Alzheimer’s disease as they get older.

The National Institute on Aging reports that 50% or more of people living with Down syndrome may develop Alzheimer’s, often with symptoms appearing during their 50s or 60s.

Is Frontotemporal Dementia Hereditary?

Frontotemporal dementia, or FTD, has a stronger genetic component than many other common dementias.

According to the U.S.-based Association for Frontotemporal Degeneration, researchers have identified more than a dozen genes that can cause FTD.

Three of the most important are:

• C9orf72
• GRN
• MAPT

At least half of people diagnosed with FTD have no known family history of the disorder. However, approximately 40% have a family history that includes another relative with a neurodegenerative condition.

When FTD is caused by one of the known autosomal dominant genetic variants, children and siblings of the affected person may have a 50% chance of inheriting the same variant.

A strong family history of FTD, ALS, unexplained early dementia, major personality changes or progressive language problems is therefore worth discussing with a specialist.

Is Lewy Body Dementia Hereditary?

Lewy body dementia is generally not considered a hereditary disease.

Having a family member with Lewy body dementia may slightly increase a person’s risk, and researchers have identified genetic variants associated with the condition.

However, hereditary forms are rare.

The Lewy Body Dementia Association notes that genetic testing is not routinely used to diagnose Lewy body dementia because currently available genetic tests cannot accurately predict who will develop it.

Is Vascular Dementia Hereditary?

Most vascular dementia is not directly inherited.

However, some of the health problems that increase vascular dementia risk can run in families. These include:

• High blood pressure
• High cholesterol
• Diabetes
• Heart disease
• Stroke risk

These conditions can be influenced by both genetics and shared lifestyle factors.

Vascular dementia results from damage to blood vessels that reduces blood flow and oxygen to the brain. Managing cardiovascular risk is therefore an important part of reducing vascular dementia risk.

CADASIL – A Rare Inherited Form

There is one particularly important exception.

CADASIL – cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy – is a rare inherited disease affecting small blood vessels in the brain.

According to the National Institute of Neurological Disorders and Stroke, CADASIL can cause migraines, strokes, mood or behavior changes, and progressive problems with thinking and memory.

It is a genuine inherited cause of vascular cognitive impairment and dementia, but it is extremely uncommon compared with ordinary vascular dementia.

Other Rare Hereditary Causes of Dementia

Some other uncommon neurological disorders can also be inherited and may cause dementia.

For example, hereditary forms of prion disease can result from genetic changes affecting the prion protein gene.

The National Institute of Neurological Disorders and Stroke explains that genetic forms of Creutzfeldt-Jakob disease and related prion diseases can be passed from parent to child.

These conditions are very rare and should not be confused with the far more common forms of Alzheimer’s disease or age-related dementia.

When Is Family History More Concerning?

If you are wondering is dementia hereditary because several relatives have been affected, the pattern within the family is important.

A genetic cause may deserve closer investigation when:

• Several people in successive generations have developed dementia.
• Dementia repeatedly begins before age 65.
• Someone develops symptoms in their 30s, 40s or 50s.
• There is a family history of frontotemporal dementia or ALS.
• Several relatives have similar neurological symptoms.
• A known disease-causing genetic variant has already been identified in the family.

A single parent developing dementia very late in life usually presents a very different genetic picture from multiple relatives developing the same disorder at unusually young ages.

Hereditary Dementia and the 50% Inheritance Pattern

Several rare genetic forms of dementia follow what is known as an autosomal dominant inheritance pattern.

This means that a person only needs to inherit one disease-causing copy of the gene from one biological parent.

If a parent carries one of these variants, each child generally has a 50% chance of inheriting that genetic variant.

This applies to conditions such as autosomal dominant Alzheimer’s disease and many known genetic forms of frontotemporal dementia.

Importantly, this 50% figure should not be applied to ordinary late-onset dementia.

If your mother or father develops Alzheimer’s at age 80, for example, that does not mean that you have a 50% chance of developing Alzheimer’s.

Should You Have Genetic Testing for Dementia?

Most people with a parent or grandparent who developed dementia do not need genetic testing.

The National Institute on Aging states that genetic testing is not routinely used to predict whether someone will develop Alzheimer’s disease or another dementia.

Testing may be considered when there is:

• Very early onset of symptoms
• A strong pattern of dementia across several generations
• A family history suggestive of autosomal dominant Alzheimer’s disease
• A suspected inherited form of frontotemporal dementia
• A known genetic variant already identified within the family

Testing for APOE ε4 is commercially available, but APOE is a risk gene rather than a straightforward Alzheimer’s test.

An APOE result cannot tell a healthy person with certainty whether they will or will not develop Alzheimer’s disease.

The Alzheimer’s Association recommends discussing genetic testing with a doctor or genetic counselor rather than trying to interpret the results alone.

Why Genetic Counseling Matters

Genetic information can affect more than the individual being tested.

A positive result may also provide information about siblings, children and other biological relatives.

For this reason, genetic counseling can help families understand:

• What a particular genetic test can and cannot tell them
• The chance of inheriting or passing on a variant
• The emotional impact of learning the result
• Whether testing other relatives would be useful
• How the result might affect future medical decisions

If My Parent Has Dementia, Will I Get It?

No. A parent having dementia does not mean that you will inevitably develop it.

The National Institute on Aging summarizes this well: a family history of Alzheimer’s may make you more likely to develop the disease, but it does not mean that you definitely will.

Your individual risk depends on many factors, including:

• Age
• Genetics
• Cardiovascular health
• Blood pressure
• Diabetes
• Smoking
• Physical activity
• Other health and lifestyle factors

Can You Reduce Dementia Risk if It Runs in Your Family?

You cannot change the genes you inherited, but many factors related to brain and cardiovascular health can be influenced.

Helpful steps include:

• Not smoking
• Being physically active
• Managing high blood pressure
• Managing diabetes
• Keeping cholesterol under control
• Following a nutritious, balanced diet
• Maintaining social connections
• Addressing hearing problems
• Discussing cardiovascular and dementia risk with your doctor

You can read more in our guide to reducing the risk of dementia.

Is Dementia Hereditary? Final Thoughts

So, is dementia hereditary? For most families, dementia is not inherited in a simple or inevitable way.

Genes can influence risk, and having close relatives with dementia can increase the likelihood of developing the condition. But genes are only part of the picture for most cases of late-onset dementia.

Rare forms are different. Specific variants in genes such as APP, PSEN1 and PSEN2 can cause inherited Alzheimer’s disease, while genetic forms of frontotemporal dementia can involve genes including C9orf72, GRN and MAPT.

Lewy body dementia is generally not considered hereditary, and most vascular dementia is not directly inherited, although rare genetic conditions such as CADASIL can cause inherited vascular dementia.

If several close relatives have developed dementia at unusually young ages, or if a known genetic condition runs in your family, talk with your doctor about whether referral to a neurologist or genetic counselor would be appropriate.