carries two copies of a gene linked to an increased risk of , reported on November 18. The middle Hemsworth brother, 39, made the discovery while filming Limitless, his forthcoming National Geographic docuseries about “pushing back on the natural decline that comes with time and aging,” per VF.On the show, Hemsworth called the discovery “my biggest fear." Though the results are not a guarantee of an Alzheimer's diagnosis, Hemsworth says they make him “8-10” times more likely to develop the disease. “It really triggered something in me to want to take some time off,” Hemsworth told VF in an interview. “And since we finished the show, I've been completing the things I was already contracted to do.