American scientists have identified a genetic variation that affects the biological clock so strongly that it can indicate at what time of the day a person is most likely to die.
The author of the study, Andrew Lim of the Beth Israel Medical Center (USA, Boston), found that the internal biological clock affects the timing of acute clinical conditions, such as stroke or heart attack.
Lim and colleagues were looking for genetic traits that indicate an increased risk of developing Alzheimer's disease or Parkinson's disease. The study involved about 1.2 thousand people over 65 years old. All of them constantly wore a special bracelet that recorded the change in sleep and wakefulness.
The study took an unexpected turn when scientists decoded the participants' genomes. It turned out that "larks" - people who tend to get up early and fall asleep early, have genetic differences from "owls" - those who tend to sleep longer in the morning and go to bed later in the evening.
Lim's group found a single nucleotide (nitrogenous base, the "building block" of the DNA molecule) next to the "Period 1" gene, which is different in "larks" and "owls". About 60% of people have adenine (A) at this point, and 40% have guanine (G).
Since a person has a double set of chromosomes, each of us has a set of AA, GG or AG.
As it turned out, people with the AA combination woke up about an hour earlier than the carriers of the GG combination, and those who had an AG "record" in their genome - half an hour later than the first.
When the researchers analyzed the deaths among the participants in the experiment (many of whom joined 15 years ago, at the age of 65), they found that this same genetic variation could indicate the hour of death.
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People with AA or AG in the genotype died shortly before 11 am, like most people, while carriers of GG with an average died shortly before 6 pm.
Lim notes that more research is needed to determine the mechanisms that link certain genetic traits to the characteristics of the biological clock.