Frontotemporal dementia starts with damage to nerve cells in the front and side of the brain

Frontotemporal dementia (FTD) is caused by the death of nerve cells in the frontal and temporal lobes — the parts of your brain that control personality, behavior, language, and decision-making. Unlike Alzheimer's disease, which typically begins with memory loss, FTD usually shows up first as changes in how someone acts, speaks, or makes decisions. The nerve cell damage happens because of abnormal proteins that build up inside brain cells and kill them over time.

The disease progresses because these damaged proteins spread from cell to cell, destroying more of the frontal and temporal lobes as months and years pass. This is why FTD often looks different from person to person — it depends on which part of the brain is affected first and how quickly the damage spreads. Someone might become withdrawn and lose interest in things they loved, while another person might become impulsive or say inappropriate things they never would have before.

Key Takeaways

  • Frontotemporal dementia is caused by abnormal proteins that accumulate inside brain cells in the frontal and temporal lobes, killing nerve cells over time.
  • The disease typically appears first as personality or behavior changes, not memory loss, which makes it different from Alzheimer's disease.
  • About 10 percent of FTD cases run in families because of inherited genetic mutations, though most cases occur without a family history.
  • The specific proteins involved — tau, TDP-43, or FUS — determine which variant of FTD someone has and how the disease will progress.
  • Diagnosis requires imaging and sometimes a spinal tap or genetic testing, because no single blood test can confirm FTD.

The role of abnormal proteins in nerve cell death

Three main types of abnormal proteins cause FTD: tau, TDP-43, and FUS. In a healthy brain, these proteins have normal jobs — tau helps stabilize the internal structure of nerve cells, and TDP-43 and FUS help control which genes are turned on or off. But in FTD, these proteins misfold, clump together, and accumulate inside or around nerve cells until the cells can no longer function and die.

Which protein is involved determines the specific variant of FTD and often predicts how the disease will progress. Someone with tau-related FTD may experience different symptoms and a different disease course than someone with TDP-43. Researchers can identify which protein is causing the damage through brain imaging, a spinal tap that measures protein levels in cerebrospinal fluid, or genetic testing — though a definitive diagnosis sometimes requires a brain biopsy after death.

The buildup of these proteins is not something a person can catch or prevent through lifestyle choices. It appears to be a process that starts in the brain years before symptoms appear, which is why someone might seem fine one day and then gradually begin showing changes in behavior or language over the following months.

Genetic mutations that run in families

About 10 percent of FTD cases are inherited, meaning a parent, grandparent, or sibling had the disease and passed down a genetic mutation that causes it. The most common genes involved are C9orf72, GRN, and MAPT. If one of your parents carries a mutation in one of these genes, you have a 50 percent chance of inheriting it — though inheriting the mutation does not may provide you will develop FTD, only that the risk is much higher.

People who carry these mutations may not show symptoms until their 40s, 50s, or 60s, and the age of onset can vary even within the same family. A parent might develop symptoms at 55 while a sibling develops them at 70. This unpredictability makes genetic testing complicated — knowing you carry a mutation means living with uncertainty about whether and when symptoms will appear.

If FTD runs in your family, genetic counseling can help you understand your own risk and what testing might show. A genetic counselor can explain what a positive result means, what it does not mean, and whether testing is right for you.

Sporadic FTD with no family history

Most people with FTD — roughly 90 percent — have no family history of the disease. In these cases, the abnormal proteins and nerve cell damage appear to develop randomly, without an inherited genetic mutation. Researchers do not yet fully understand why some people develop sporadic FTD and others do not, though age, environmental exposures, and other genetic factors that are not inherited may play a role.

Sporadic FTD is not contagious and cannot be passed to children or family members. It is not caused by anything the person did or did not do — no diet, lifestyle choice, or past injury causes the abnormal proteins to form. The disease simply develops in the brain over time, and the reason remains unknown.

How FTD differs from Alzheimer's disease

The most important difference is where the damage starts. Alzheimer's disease typically begins in the hippocampus, the part of the brain that stores new memories, so memory loss is usually the first sign. FTD begins in the frontal and temporal lobes, so personality, behavior, and language changes come first — memory often stays intact in the early stages.

Someone with early FTD might forget nothing about yesterday but become a completely different person in how they act. They might lose interest in hobbies, become socially withdrawn, make poor financial decisions, or say things that are out of character and inappropriate. A person with early Alzheimer's, by contrast, typically remembers who they are and how they usually act but cannot remember what they had for breakfast or why they walked into a room.

The proteins involved are also different. Alzheimer's is caused primarily by amyloid-beta and tau, while FTD is caused by tau, TDP-43, or FUS. This difference matters because it affects how the disease progresses and which treatments might eventually help — a drug that works for Alzheimer's may not work for FTD.

Age of onset and disease progression

FTD typically appears between ages 40 and 65, which is earlier than most other dementias. Some people develop symptoms in their 30s, while others do not show signs until their 70s, but the average age of diagnosis is around 58. This early onset often means FTD strikes people who are still working, raising children, or managing finances — which creates particular challenges for families and caregivers.

The disease progresses at different speeds depending on the person and which proteins are involved. Some people decline slowly over 10 or more years, while others decline rapidly over 3 to 5 years. There is no way to predict at diagnosis how quickly someone's symptoms will worsen, which makes planning difficult for families.

What brain imaging and testing can show

Doctors use MRI or PET scans to look for shrinkage or reduced activity in the frontal and temporal lobes. These images do not show the abnormal proteins directly, but they show the damage the proteins have caused — areas where nerve cells have died and brain tissue has atrophied. The pattern of shrinkage often matches the type of symptoms someone is experiencing.

A spinal tap can measure levels of tau, TDP-43, and other proteins in cerebrospinal fluid, which may point toward which protein is causing the damage. Genetic testing can identify inherited mutations in C9orf72, GRN, or MAPT. Blood tests that measure certain proteins are becoming more available and may eventually help with diagnosis, though they are not yet standard in all clinics.

Despite these tools, a definitive diagnosis of which protein is involved sometimes requires a brain biopsy after death. This is why some people live with a diagnosis of "probable FTD" rather than confirmed FTD — the imaging and other tests point strongly toward FTD, but the exact cause cannot be proven without examining brain tissue directly.

Frequently Asked Questions

Can you get frontotemporal dementia from a head injury?

There is no proven link between a single head injury and FTD. However, repeated head trauma over many years — such as in contact sports — may increase dementia risk in general. FTD itself is caused by abnormal proteins that develop in the brain, not by injury.

If my parent has FTD, will I definitely get it?

Only if your parent carries one of the inherited genetic mutations (C9orf72, GRN, or MAPT). If they do, you have a 50 percent chance of inheriting it. But inheriting the mutation does not may provide you will develop symptoms — some people carry the mutation and never show signs of disease.

Is there a blood test that can diagnose frontotemporal dementia?

Blood tests that measure certain proteins are becoming available and may help support a diagnosis, but they are not yet standard or definitive. Diagnosis still relies mainly on brain imaging, clinical symptoms, and sometimes a spinal tap or genetic testing.

Does frontotemporal dementia run in families?

About 10 percent of FTD cases are inherited. If it runs in your family, genetic counseling can help you understand your risk and whether testing makes sense for you. The other 90 percent of cases appear to develop randomly without a family history.

Why does frontotemporal dementia start so early compared to other dementias?

The reason is not fully understood. FTD typically appears in the 40s to 60s, while Alzheimer's usually appears later. Researchers are still studying why the abnormal proteins in FTD develop earlier in life than the proteins that cause other dementias.