Chris Hemsworth discovers he has rare genetic makeup that significantly increases risk of Alzheimer's disease: "My biggest fear"

Chris Hemsworth's new show with National Geographic on Disney Plus is "a mission to live better for longer." But because of that show, he has come face-to-face with his "biggest fear" – that he might develop Alzheimer's disease.

During one episode of the show, the 39-year-old "Thor" actor underwent genetic testing to learn more about his present and future health. It turns out that Hemsworth has a rare genetic makeup with two copies of the APO4 gene, which has been connected to an increased risk of Alzheimer's disease. 

"ApoE4 is the strongest risk factor gene for Alzheimer's disease," a 2021 study by the National Institutes of Health says, "although inheriting ApoE4 does not mean a person will definitely develop the disease."