November 17, 2012
Genetic Variants Could Predict Time Of Death And Whether You Are A Night Owl Or Early Bird
redOrbit Staff & Wire Reports - Your Universe Online
Scientists have for the first time identified a common gene variant which not only determines whether or not a person is an early riser or a night owl, but could also indicate what time of day an individual is likely to die.
The research, which is published in this month's edition of the Annals of Neurology, was conducted at the Department of Neurology at Beth Israel Deaconess Medical Center (BIDMC). It revealed variation in a lone nucleotide located near a gene known as "Period 1" between two different study groups that exhibited different wake-sleep behavior patterns.
"Many of the body's processes follow a natural daily rhythm or so-called circadian clock. There are certain times of the day when a person is most alert, when blood pressure is highest, and when the heart is most efficient," the BIDMC explained in a Friday press statement. "Several rare gene mutations have been found that can adjust this clock in humans, responsible for entire families in which people wake up at 3 a.m. or 4 a.m. and cannot stay up much after 8 at night."
The variant discovered by the researchers impacts "virtually the entire population" and "is responsible for up to an hour a day of your tendency to be an early riser or night owl," they added. The discovery "could help with scheduling shift work and planning medical treatments, as well as in monitoring the conditions of vulnerable patients."
First author Dr. Andrew Lim, an Assistant Professor in the Division of Neurology at the University of Toronto, who began the study about 15 years ago while he was a postdoctoral fellow at the BIDMC Department of Neurology, explained that the circadian clock (commonly referred to as the biological clock) is responsible for determining a person's sleep habits, as well as their ideal mental and physiological performance times.
He also says that it can influence "the timing of acute medical events like stroke and heart attack."
Lim and his colleagues began their work several years ago while attempting to discover why seniors were having difficulty sleeping. The BIDMC team and colleagues at Chicago's Rush University had recruited 1,200 healthy, 65-year-old individuals, who agreed to undergo neurological and psychiatric evaluations once a year, the medical center explained.
"The cohort's original intent was to determine if there were identifiable precursors to the development of Parkinson's disease or Alzheimer's disease," they said. "As part of the research the subjects were undergoing various sleep-wake analyses using a wristband called an actigraph, which provides a reliable record of an individual's pattern of activity. Additionally, in order to provide the scientists with information on sleep-wake patterns within a year of death, the participants had agreed to donate their brains after they died."
"But the investigation took a new turn when Lim learned that the same group of subjects had also had their DNA genotyped," BIDMC officials added. "Teaming up with investigators from Brigham and Women's Hospital (BWH), Lim and his colleagues compared the wake-sleep behavior of these individuals with their genotypes. These findings were later verified in a group of young volunteers."
It was shortly after this that they located the nucleotide variation in the "Period 1" region of the genome. There, they report, 60-percent of the people have adenine (A) nucleotide bases and 40-percent at guanine (G) nucleotide bases. Due to each individual having two chromosome sets, there is a roughly 36-percent chance of having a pair of A bases, a 16-percent of having two G bases, and a 48-percent chance of having one of each.
"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," BIDMC Chief of Neurology Clifford Saper, the man in charge of the laboratory where Lin began his work, said.
Additional research determined that the variant could affect the body's so-called circadian rhythm in other ways, including the projected time of death. According to Saper, the average person is likely to die sometime in the late morning hours (with 11am being the average time of death).
The researchers went back to the 65-year-old subjects who had passed on since the beginning of the study, and learned that "this same genotype predicted six hours of the variation in the time of death: those with the AA or AG genotype died just before 11 a.m., like most of the population, but those with the GG genotype on average died at just before 6 p.m."
Along with Lin and Saper, credited co-authors of the study include Drs. Anne-Marie Chang, Joshua M. Shulman, Towfique Raj, Lori B. Chibnik, Sean W. Can, Katherine Rothamel, Christophe Benoist, Amanda J. Myers, Charles A. Czeisler, Aron S. Buchman, David A Bennett, Jeanne F. Duffy, and Philip L. De Jager.