Frontotemporal dementia (FTD) is caused by progressive damage to neurons in the frontal and temporal lobes of the brain, the regions that control personality, behavior, and language. Unlike Alzheimer’s, which typically strikes after age 65, FTD usually develops in the sixth decade of life and is the most common form of dementia in people under 60. The underlying triggers are a mix of genetics, abnormal protein buildup, and, in some cases, environmental exposures.
Genetics Play a Larger Role Than in Most Dementias
FTD is one of the most heritable forms of dementia. About 40% of people diagnosed have a family history of dementia, and roughly 15% to 40% of all cases trace back to a single-gene mutation passed down in families. In those familial cases, two genes account for about half: one involved in producing a structural protein called tau, and another involved in producing a protein called progranulin, which helps keep brain cells healthy. A third mutation, identified in 2011, involves an abnormal repeat of a short DNA sequence and accounts for another 10% to 30% of inherited cases. This third mutation is also linked to ALS (Lou Gehrig’s disease), which is why some families see both conditions.
These mutations follow an autosomal dominant inheritance pattern, meaning a child of someone carrying the mutation has a 50% chance of inheriting it. But having a family history doesn’t guarantee a genetic cause. In one Colombian study that classified patients by genetic risk, about 54% of FTD cases were sporadic, with no clear family link. Known mutations explain only a fraction of cases overall, which means other genetic risk factors and non-genetic causes are still being identified.
Abnormal Proteins Accumulate and Kill Neurons
Regardless of whether the cause is genetic or sporadic, FTD ultimately comes down to toxic proteins building up inside brain cells. Three proteins are most commonly involved: tau, TDP-43, and FUS. In healthy brains, these proteins serve important functions. Tau stabilizes the internal scaffolding of neurons. TDP-43 helps regulate how genes are read and translated inside the cell nucleus. FUS plays a similar role in processing genetic instructions.
When these proteins misfold and clump together, they interfere with basic cell operations. TDP-43, for instance, disrupts the transport system between a cell’s nucleus and the rest of the cell. Proteins that should get into the nucleus can’t, and genetic messages that should get out become trapped. Over time, neurons starved of normal function begin to die. In cases linked to progranulin gene mutations, the problem starts even earlier in the chain: the brain’s immune cells (microglia) lose the ability to clean up cellular debris. Their internal recycling machinery, the lysosome, stops working properly, and waste products like fragments of the insulating coating around nerve fibers pile up. This debris buildup triggers inflammation in white matter and contributes to TDP-43 accumulation in nearby neurons.
Different Variants Damage Different Brain Regions
FTD isn’t a single disease. It comes in several clinical forms, and which form develops depends on where the brain loses the most tissue. The behavioral variant (bvFTD) is the most common. It causes personality changes, loss of empathy, impulsive behavior, and apathy. Brain imaging shows that bvFTD patients have the most severe shrinkage in the frontal lobes, particularly the white matter that connects frontal regions. Volume loss in a specific area called the ventromedial prefrontal cortex, the part of the brain involved in social decision-making and emotional regulation, directly correlates with how severe behavioral symptoms are at the time of diagnosis.
The language variants, grouped under the term primary progressive aphasia (PPA), affect different parts of the brain. Semantic PPA, which erodes the ability to understand word meanings and recognize objects, causes the most damage in the fusiform gyrus, a structure on the underside of the brain important for recognizing faces and linking words to concepts. Nonfluent PPA, which makes speech slow and effortful, shows more shrinkage in the parietal lobes compared to both the behavioral variant and semantic PPA. These distinct patterns of atrophy explain why people with the same underlying disease can look so different from one another.
Environmental and Lifestyle Risk Factors
Most research on FTD has focused on genetics, but a growing body of evidence points to environmental triggers, especially in cases without a clear family history. A case-control study in Northern Italy found elevated risk among people with occupational exposure to aluminum, pesticides, and chemicals like dyes, paints, or thinners. These associations were particularly strong for the frontotemporal dementia subgroup specifically, not just early-onset dementia in general.
Head trauma also appears to be a risk factor. While a history of any trauma requiring medical attention didn’t significantly raise overall early-onset dementia risk, the analysis showed a notably higher association when limited to head injuries, with the odds ratio climbing to 3.4 for FTD specifically. Playing football (soccer), which involves repeated heading of the ball, was linked to higher risk, while overall sports practice without head-impact exposure appeared protective. Smoking was another consistent risk factor, likely through its effects on blood vessels supplying the brain. Long-term use of selenium-containing dietary supplements also showed a positive association, though the mechanism isn’t well understood.
How FTD Is Identified
Diagnosing FTD is notoriously difficult because early symptoms often mimic psychiatric conditions like depression, bipolar disorder, or even schizophrenia, particularly in younger patients. Brain imaging can reveal patterns of frontal and temporal lobe shrinkage, but this is most apparent after the disease has progressed.
A blood-based marker called neurofilament light chain (NfL), which is released when nerve fibers are damaged, has shown strong promise. In one study, a specific threshold distinguished true FTD from FTD “phenocopies” (conditions that look like FTD but aren’t) with 91.5% sensitivity and 100% specificity. NfL levels in plasma are already being used in clinical trials and may become part of routine diagnostic workups as research continues. Genetic testing is available for people with a strong family history and can identify mutations in the three major genes associated with the disease.
Treatments Targeting the Root Cause
There is no approved treatment that slows or stops FTD, but several clinical trials are targeting the genetic roots of the disease. Most current trials focus on people with progranulin gene mutations, since that pathway is the furthest along in drug development. The core idea is straightforward: if the disease is caused by too little progranulin in the brain, restoring progranulin levels should reduce damage.
Researchers are testing multiple approaches to achieve this. One strategy uses an antibody delivered intravenously that blocks a protein responsible for breaking down progranulin too quickly. This drug received Breakthrough Therapy Designation from the FDA in 2024 and has completed Phase 3 enrollment, with results expected by the end of 2025. Other trials are testing gene therapies that deliver a working copy of the progranulin gene directly into the brain through injection, and at least one trial is testing a protein replacement approach that ferries progranulin across the blood-brain barrier using a specialized delivery technology. Several of these programs hold Orphan Drug or Fast Track designations, reflecting the urgency and the lack of existing options. Results from these trials will likely inform approaches for sporadic FTD as well, even though the initial focus is on genetically defined cases.