Is Behavioral Variant FTD Hereditary? Genetic Risk Explained for Families

If you or a loved one has been diagnosed with behavioral variant frontotemporal dementia (bvFTD), it is entirely natural to worry about what this means for your children.

The short answer is: bvFTD can be hereditary, but it is not always passed down.

A diagnosis of bvFTD alone does not automatically mean your children are at high risk. Between 20% and 50% of all frontotemporal dementia (FTD) cases are considered familial, meaning there is a pattern of the disease in the family history or a known genetic cause ^[1][2]. The rest are considered sporadic, occurring by chance without a clear genetic link. However, it is possible to carry a genetic mutation for the disease even if you do not have a known family history ^[3].

The Major Genetic Causes

Most known genetic cases of bvFTD are caused by mutations in one of three specific genes ^[4]:

• C9orf72: This is the most common genetic cause of FTD. It is also strongly linked to amyotrophic lateral sclerosis (ALS, or Lou Gehrig’s disease) ^[5]. The symptoms, the age they begin, and the severity can vary widely from person to person, even within the same family ^[6].
• MAPT: Mutations in this gene lead to abnormal buildups of a protein called tau in the brain ^[4]. It is closely associated with bvFTD and sometimes movement issues similar to Parkinson’s disease (parkinsonism).
• GRN: Mutations in this gene affect a protective protein called progranulin, which is associated with the buildup of another protein (TDP-43) in the brain ^[4].

While these three genes are the most common, researchers have identified several other, rarer genes linked to FTD, and some families with clear inheritance patterns have no identifiable mutation yet ^[1].

Understanding Autosomal Dominant Inheritance

When bvFTD is caused by a mutation in C9orf72, MAPT, or GRN, it usually follows an autosomal dominant inheritance pattern.

If a parent is confirmed through genetic testing to have one of these disease-causing mutations, each biological child has a 50% chance of inheriting that specific mutation ^[7]. It is similar to flipping a coin. If a child does not inherit the familial mutation, they cannot pass that specific mutation on to their future children.

Importantly, inheriting a mutation does not mean a 100% guarantee of developing dementia. This concept is called penetrance—the proportion of people with a genetic variant who actually develop symptoms over their lifetime. Especially with the C9orf72 gene, penetrance is age-related and can be incomplete, meaning some people with the gene may never develop symptoms, or may develop them at a completely different age than their parent did ^[6].

Testing Strategy: What the Results Mean

If you are concerned about your children’s risk, medical guidelines recommend that the person who already has bvFTD be tested first, rather than testing the children directly ^[8]. This is the most informative way to find out if a hereditary gene is present in the family.

Testing the affected person can yield three types of results ^[8]:

• Positive (Pathogenic Variant): A known disease-causing mutation is found. If this happens, adult children can then decide if they want to undergo “predictive testing” to see if they inherited the specific gene.
• Negative: No known mutations are found. This is reassuring, but it does not completely rule out a genetic cause because science has not yet discovered every gene responsible for FTD.
• Variant of Uncertain Significance (VUS): A genetic change is found, but doctors do not currently know if it causes disease. A VUS should not be used to predict a child’s risk, make reproductive decisions, or alter medical care.

The Vital Role of Genetic Counseling

Because of the heavy emotional weight and uncertainty involved, you should meet with a genetic counselor before pursuing testing ^[8][9]. A genetic counselor helps your family navigate:

• Choosing the Right Test: Standard genetic panels might miss certain mutations (like the C9orf72 “repeat expansion”), so specialized testing is often required ^[8].
• Emotional and Social Impact: Knowing you carry a gene for dementia can profoundly affect your self-image, relationships, and anxiety levels, even if it helps with future planning ^[10]. Negative results can bring relief, but the waiting process is stressful.
• Family Dynamics: Predictive testing for adult-onset conditions is completely voluntary. It is up to each adult child to decide if, and when, they want to know their genetic status. Testing minors for adult-onset diseases is generally not recommended.
• Insurance and Privacy Considerations: While laws in some countries protect your health insurance and employment from genetic discrimination, these protections often do not apply to life insurance, disability insurance, or long-term care insurance.
• Family Planning: For families who want to know, counselors can discuss reproductive options, such as in vitro fertilization (IVF) with genetic testing of embryos, to prevent passing a known mutation to the next generation.