Rumer Willis has opened up about undergoing genetic testing after her father, actor Bruce Willis, was diagnosed with frontotemporal dementia (FTD), describing the experience as 'terrifying'.

The 38-year-old actress said she wanted to understand her own health risks as her family navigates Bruce Willis' ongoing illness. She has also spoken about a wider family history that includes breast cancer and other health conditions.

Willis underwent an APOE genetic test, which looks at variants associated with a person's risk of developing Alzheimer's disease. She said her result showed a 'pretty average' risk.

But what does that actually mean, and does having a parent with dementia mean their children will develop the condition?

What Is Frontotemporal Dementia?

Bruce Willis was diagnosed with FTD in 2023 after initially being diagnosed with aphasia. FTD is a group of disorders caused by progressive damage to the frontal and temporal lobes of the brain.

Unlike Alzheimer's disease, which commonly affects memory in its early stages, FTD can initially cause changes in behaviour, personality, language, and communication. The condition is relatively uncommon compared with Alzheimer's disease and is one of the more common causes of dementia in people younger than 65.

Importantly, having a parent with FTD does not automatically mean their children will develop it. Most dementia cases are not inherited in a straightforward way. However, some rarer forms of FTD can have a strong genetic component, particularly when several close relatives have developed the condition at relatively young ages.

What Does the APOE Test Show?

The APOE gene provides instructions for making a protein involved in transporting fats and cholesterol around the body.

There are three common versions, or alleles, of the gene: APOE ε2, APOE ε3, and APOE ε4. Having one or two copies of APOE ε4 is associated with a higher risk of Alzheimer's disease. However, it is not a diagnosis and does not mean someone will definitely develop dementia.

Similarly, having no APOE ε4 does not guarantee that a person will never develop Alzheimer's. This distinction is particularly important in Willis' case. Her APOE result relates primarily to Alzheimer's disease risk, not whether she will inherit her father's specific form of dementia, FTD.

Does Family History Increase Dementia Risk?

Family history can matter, but the relationship is complicated. A person with a close relative who has dementia may have a higher risk of developing the condition themselves, depending on the type of dementia and the age at which the relative developed it.

For some inherited forms of FTD, specific genetic mutations can substantially increase risk. These are different from the APOE variants commonly discussed in relation to Alzheimer's disease.

Genetic counselling can therefore be useful for people concerned about a strong family history. Specialists can examine a person's family tree, the ages at which relatives developed symptoms, and the type of dementia involved before deciding whether genetic testing is appropriate.

Is Genetic Testing Right for Everyone?

Not necessarily. Genetic tests can provide useful information, but they can also create anxiety or confusion if results are interpreted without appropriate medical context.

A result showing increased genetic risk does not necessarily predict an individual's future with certainty. Lifestyle, age, other genes, and environmental factors can all influence whether a disease develops.

There are also emotional and practical considerations. Willis described receiving answers as frightening, although she ultimately viewed having more information as empowering.

For people considering testing because of a family history of dementia, speaking with a GP, neurologist or genetic counsellor can help determine which test, if any, would actually provide useful information.

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