It appears the Grim Reaper has a schedule to keep.

A team of scientists led by a University of Toronto neurology professor says it has discovered a gene mutation that determines the time of day a person is most likely to die.

“It’s just kind of spooky. I just couldn’t believe it,” said co-author and Harvard University professor Dr. Clifford Saper.

The study, led by University of Toronto professor Dr. Andrew Lim and published in the November edition of Annals of Neurology, emerged from research into seniors’ sleep-wake cycles.

Analyzing 1,200 people who had enrolled in another study as healthy 65-year-olds about 15 years earlier, the researchers set out to investigate why seniors have trouble sleeping and whether they could identify signs of oncoming Parkinson’s or Alzheimer’s disease.

But the study changed tack when Lim discovered a link between sleep patterns and variations in “Period 1,” the gene that plays a major role in the internal biological — or circadian — clock.

The team found that people who report waking early in the morning (before 7 a.m.) are more likely to have an adenine (A-A) nucleotide base. Late-risers, on the other hand, are more likely to have a guanine (G-G) nucleotide base. Those who wake up somewhere in the middle have both (A-G).

Having made the link, Lim then wondered whether the mutation played a role in death, so he went back to the database and cross-compared times of death and DNA from those who had passed away. Like sleep, he discovered a circadian rhythm of death.

Barring accidental causes, early risers (A-A’s and A-G’s) are more likely to die at around 11 a.m., while late risers (G-G’s) will more likely hold out until around 6 p.m.

“It is a bit disconcerting that something as fundamental as the time one is likeliest to die can be influenced by a simple gene variant,” said Lim in an email, adding that 17 per cent of people with the G-G variation died an average of six hours later than others.

Saper said the laboratory test is relatively simple and requires only a small amount of DNA, whether it’s blood or saliva. But will he take it?

“No,” he said. “I’ll let it be up to the fates.”