"The internal 'biological clock' regulates many aspects of human biology and behavior, such as preferred sleep times, times of peak cognitive performance, and the timing of many physiological processes. It also influences the timing of acute medical events like stroke and heart attack," said Andrew Lim, a study author and a postdoctoral fellow at Beth Israel Deaconess Medical Center at the time of this research.
Researchers had previously been aware of certain rare gene mutations that meant that entire families were on the same Circadian rhythm, in which they stayed awake until the wee hours of the morning and woke up in the early afternoon. However, this study was the first to find a gene that is expressed in every single member of the general population.
The study, published in the Annals of Neurology, began as an attempt to find out whether behaviors could predict the onset of the debilitating Alzheimer's and Parkinson's diseases. The study had intended to examine 1,200 people who were 65 years old at the time of study. Researchers also gave the participants actigraphs, which analyze a person's sleep-wake behaviors and provides an assessment of their activity. All of the participants also agreed to donate their brains after their deaths.
The investigation took a turn though when Lim discovered that the participants had previously had their DNA genotyped. The researchers compared the patients' sleeping and waking rhythms with their genotypes. This evidence was also corroborated with that of younger participants.
The researchers found two nucleotides by a gene named "Period 1" that were key: adenine (A), which was present in 60 percent of participants, and guanine (G), present in 40 percent. Because each person has two sets of chromosomes, there is a 36 percent chance that a person is AA, a 16 percent that a person is GG, and a 48 percent chance that a person has an A and a G at this location.
"This particular genotype affects the sleep-wake pattern of virtually everyone walking around, and it is a fairly profound effect so that the people who have the A-A genotype wake up about an hour earlier than the people who have the G-G genotype, and the A-Gs wake up almost exactly in the middle," Clifford Saper, from Harvard Medical School and one of the study authors, said in a statement.
That gene also has effects on the time of day that a person will die. "Virtually all physiological processes have a circadian rhythm, meaning that they occur predominantly at certain parts of the day. There's even a circadian rhythm of death, so that in the general population people tend on average to be most likely to die in the morning hours. Sometime around 11 am is the average time," Saper explained.
Researchers found that the nucleotide caused some variation in this time, however. For people who were AA or AG, they were likely to die shortly before 11 AM. People who were GG, on the other hand, were more likely to die before shortly 6 PM.
"So there is really a gene that predicts the time of day that you'll die. Not the date, fortunately, but the time of day," Saper says.
The findings could influence how medications are administered, so that they are suggested at particular times according to a person's Circadian rhythm. Studying this process could also help eliminate confusion of the Circadian rhythm, especially for the ghastly jet lag.