"Apart from a few highly penetrant genes that confer significant cancer risk, the role of heredity factors remains poorly understood, and most malignancies are assumed to result from random errors during cell division or bad luck," said Christina Curtis, PhD, the RZ Cao Professor of Medicine and a professor of genetics and of biomedical data science.

“It would give us a better sense of how penetrant the virus is in our communities,” said William Schaffner, an infectious disease specialist at Vanderbilt University.

Only five per cent of disease-related gene mutations are fully penetrant, which means they guarantee the disease.

Less than 5% of the ones tied to Alzheimer’s are “fully penetrant,” meaning that they guarantee you’ll get the disease, he said.

The PSEN1 mutation is associated with an early-onset form of Alzheimer’s, and it is often described as “100 percent penetrant,” which he quickly came to understand meant no exceptions — everyone with the variant gets the disease.