Researchers have discovered a gene that is associated with the timing of one's sleep-wake rhythm or cycle, as well as one's likeliest time of death.
"This gene variant influences both the earliness or lateness of one's sleep and activity rhythms as well as the clock time of day one is likeliest to die," says Dr. Andrew Lim, lead author of the study and a neurologist at Sunnybrook Health Sciences Centre. "This information could be potentially helpful in the scheduling of shift work or schooling, and if we know when a person is likeliest to die, we can act to prevent this by administering medical treatments at more optimal times, and better monitor vulnerable patient populations."
Published in the November 2012 issue of Annals of Neurology, the findings emerged from research that initially set out 15 years ago to investigate risk factors for Alzheimer's disease.
As part of this larger study, the investigators measured sleep/wake and activity rhythms in a large number of older individuals and obtained DNA from them. They used this opportunity to search for common gene variants that might play a role in the internal biological clock. In so doing, they discovered a gene variant that is associated with as much as one hour difference in the timing of people's internal biological clock. Each individual carries two copies of this gene - one from their mother and one from their father. The 16 per cent of individuals with two copies of the "late" version of the gene have sleep/wake and activity timings more than one hour later than the 36 per cent of individuals with two copies of the "early" version of the gene, with the 48 per cent of individuals with one copy of each version of gene lying in between.
Once that link was made, the researchers went back to the database to compare the times of death and DNA of those who had passed away during the course of the study, and also found an association between this gene and the time of death.
"This is exciting because it is the first gene variant shown to influence the timing of directly recorded human sleep and activity rhythms and also time of death," adds Dr. Lim, also an assistant professor at the University of Toronto.
Whereas most individuals were likeliest to die in the late morning or early afternoon, individuals with two copies of the "late" version of the gene were likeliest to die later in the day, in the early evening at around 6 p.m.