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Early riser, night owl and time of death is all in the genes

Kathleen Blanchard's picture
Huge study finds genes predict when we awaken, go to sleep and die.

Researchers have discovered a gene variant that is present in the entire population that determines whether we are night owls or early birds and is determined by our DNA. In the surprising finding, scientists also found the genetic variant helps determine the time of day a person will die.

First author Andrew Lim, MD, who conducted the work as a postdoctoral fellow in the Department of Neurology at Beth Israel Deaconess Medical Center (BIDMC) explained in a press release how our ‘biological clock’ or Circadian rhythm regulates when we sleep, when we’re most alert and the timing of “many physiological processes” – including death.

Lim, who is currently an Assistant Professor in the Division of Neurology at the University of Toronto, explained studies conducted on twins in family suggest the lateness or earliness of a person’s biological clock might be hereditary. Animal studies suggest otherwise; that earliness the lateness might be influenced by specific genes.

What Lim and his team have discovered is that there are three gene variations that control the sleep wake cycle and time of death for the entire population.

The research started when Lim and was studying why older people have trouble sleeping.

During his research at BIDMC, Lim and Chief of Neurology Clifford Saper, MD, PhD and colleagues were trying to identify precursors to Parkinson’s and Alzheimer’s disease as part of our research project involving 1,200 healthy 65 year olds who consented to an annual neurological and psychiatric exam.

The participants were also undergoing sleep-wake exams using a device called a wrist actigraph that measures activity. The volunteers also consented to donate their brains after they died.

When Lim discovered the adults also had their DNA genotyped, Lim and his colleagues compared the study participant’s genes to their sleep-wake cycle, finding that how genes are paired predicts when we awaken from sleep.

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The researchers also found people with two of the genotypes died just before 11:00 AM like most of the population, but those with another died just before 6:00 PM.

Specifically, a nucleotide (groups of molecule that build DNA) near a gene called "Period 1" dictates the sleep wake period among 2 groups of people, found in the study.

Sapler says "...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."

The researchers explain 60 percent of people have the nucleotide base adenine (A) and 40 percent have the nucleotide base termed guanine (G). Because we have two chromosomes, we all have adenine, guanine or a combination of the gene base.

The study authors suggest understanding more about how genes influence our biological clocks and even predict what time of day we will die has practical applications for shift workers, for instance, and jet lag.

Lim says understanding how the gene variants influence cause and time of death could lead to sensible interventions like knowing what time of day to take heart medications to provide protection when risk is highest.

Saper says though the gene study, which is the biggest contribution to date that targets a large population, can predict time of day a person would die it ‘fortunately’ can’t tell us what day it will happen.

Annals of Neurology
DOI: 10.1002/ana.23667
October, 2, 2012

Image credit: Morguefile