It's the ultimate unanswerable question we all face: When will I die? If we knew, would we live differently? So far, science has been no more accurate at predicting life span than a $10 fortune teller. But that’s starting to change.
The measures being developed will never get good enough to forecast an exact date or time of death, but insurance companies are already finding them useful, as are hospitals and palliative care teams. “I would love to know when I’m going to die,” says Brian Chen, a researcher who is chief science officer for Life Epigenetics, a company that services the insurance industry. “That would influence how I approach life.”
The work still needs to be made more practical, and companies have to figure out the best uses for the data. Ethicists, meanwhile, worry about how people will cope with knowing the final secret of life. But like it or not, the death predictor is coming.
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Steve Horvath, a UCLA biostatistician who grew up in Frankfurt, Germany, describes himself as “very straight,” while his identical twin brother is gay. So he had a personal interest when, a few years ago, a colleague asked him for help analyzing biological data from the saliva of twins with opposite sexual orientations. The colleague was trying to detect chemical changes that would indicate whether certain genes were turned on or off.
The hypothesis was that these so-called epigenetic changes, which alter the activity of DNA but not the DNA sequence itself, might help explain why two people with identical genes differ in this way. But Horvath found “zero signal” in the epigenetics of the twins’ saliva. Instead, what caught his attention was a powerful link between epigenetic changes and aging. “I was blown away by how strong the signal was,” he says. “I dropped most other projects in my lab and said: ‘This is the future.’”
Horvath became particularly intrigued by how certain chemical changes to cytosine—one of the four DNA bases, or “letters” of the genetic code—make genes more or less active. Given someone’s actual age, looking for these changes in that person’s DNA can tell him whether the person’s body is aging unusually fast or slowly. His team tested this epigenetic clock on 13,000 blood samples collected decades ago, from people whose subsequent date of death was known. The results revealed that the clock can be used to predict mortality.
Because most common diseases—cancer, heart disease, Alzheimer’s—are diseases of aging, the ticking of Horvath’s clock predicts how long someone will live and how much of that life will be free of these diseases (though it doesn’t foretell which ones people will get). “After five years of research, there is nobody who disputes that epigenetics predicts life span,” he says.