A genetic test promoted by Chris Hemsworth for Alzheimer’s disease is already available to patients in Australia, but is unlikely to provide useful information for most, neurologists are being advised.

The Hollywood star made headlines last month after undergoing a series of genetic tests for a wellness documentary on anti-ageing called Limitless on Disney+. The results showed that he had copies of the gene APOE4 from both his mother and father, linked to an increased risk of developing Alzheimer’s.

Hemsworth, whose grandfather has dementia, said the discovery confirmed his “biggest fear” and told Vanity Fair he had decided to take a break from acting while he adjusted to the information.

“It really triggered something in me to want to take some time off,” Hemsworth said, adding he wanted to “just simplify” and spend more time with his family.

He said he hoped the documentary would become a “motivator for people to take better care of themselves” and would raise awareness of the “preventative steps” people could take to combat Alzheimer’s.

“Most of us, we like to avoid speaking about death in the hope that we’ll somehow avoid it. We all have this belief that we’ll figure it out,” he said.

“Then to all of a sudden be told some big indicators are actually pointing to this as the route which is going to happen, the reality of it sinks in. Your own mortality.”

It remains to be seen whether the episode will prompt a spike in patients undergoing the screening, which is already available in Australia – with prices generally about $170 per test.

Absolute risk low

Nevertheless, there are major question marks over the usefulness of the results, particularly for those patients still aged in their 30s, like Chris Hemsworth.

Dr William Brooks, a clinical scientist studying the genetics of early onset Alzheimer’s disease at NeuRA in Sydney, stresses the ApoE4 allele is known to confer an increased risk of Alzheimer’s, a link established since the early 1990s.

The current research suggests that roughly 25% of Australians with one copy of the gene are at about a three-fold increased risk, while the 2-3% with two copies are up to 15 times greater risk.

“Certainly that figure sounds pretty terrible, but it’s relative, and his absolute risk is probably still quite low given it doesn’t sound like his parents have it,” he said.

As a result, Dr Brooks said he generally didn’t recommend patients undergo the testing, and certainly wouldn’t endorse it at a population level.

“For people who might want something to motivate them to adopt or adhere to habits more conducive to a healthier brain, it might be helpful,” he told the limbic.

“But keep in mind that a large proportion of people with Alzheimer’s disease don’t have an E4 allele.”

On the other hand, he said a study known as the REVEAL (Risk EValuation and Education for ALzheimer disease) trial had found disclosure did not lead to significant psychological risks.

Disclosure also gave rise to a significant rise in health seeking behaviours, including an increase in use of dietary supplements despite lack of proven benefits.

He said that while not proven in people with the ApoE4 allele, there were lifestyle changes that patients could take to maximise their brain health. These included mental and physical exercise and dietary changes.

“A combination of those does actually have an effect on your memory,” he said.

“Now the studies haven’t been going long enough to see whether these can prevent dementia, although they are more likely to delay it in my view and some recent Australian research seems to bear that out.”

Drugs were also under development that purported to delay or “bust” beta-amyloids in the brain, which could have a dementia benefit, but the evidence on this was unclear, Dr Brooks said.

He added: “But I still wouldn’t really recommend testing to anyone unless they asked for it and were really curious, and I was reasonably sure that they wouldn’t be distressed by it.”