New research suggests that those of us who have trouble falling asleep early may have a genetic mutation that delays sleep onset.
Some of us hit the snooze button far too many times before fully waking up. People who struggle to wake up early in the morning but have no problem staying up late are popularly referred to as "night owls."
Night owl behavior is often diagnosed as delayed sleep phase disorder (DSPD) by sleep clinicians. DSPD is estimated to affect 15 percent of the population of the United States.
People with DSPD have a delayed circadian rhythm. The 24-hour circadian clock aligns the internal physiology of organisms with the environment, but people with DSPD experience a delayed onset of sleep.
New research, published in the journal Cell, identifies a genetic mutation that may be responsible for altering the human circadian clock in night owl types.
The researchers - led by Michael Young, who is Richard and Jeanne Fisher Professor and head of the Laboratory of Genetics at The Rockefeller University in New York - think that a mutation in the CRY1 gene may cause sleep onset delay.
How a genetic mutation can influence our internal clock
Our circadian rhythm has a clear genetic basis that, as the authors of the new paper explain, has remained the same over the course of evolutionary history. The clock is "basically the same from flies to humans," says lead author Young.
At the beginning of the circadian cycle, the cells build up proteins called activators. Over the 24-hour cycle, these activators produce their own inhibitors that make the activators gradually diminish. When all the activators have been silenced, they no longer produce inhibitors. When all of the inhibitors have degraded, the activators regain their maximum potency, thus starting the cycle all over again.
Young and colleagues identified the CRY1 protein as one of the inhibitors, which works to repress the activator proteins Clock and Bmal1 (called ARNTL in humans). The researchers found a single-point mutation in the CRY1 gene, which means that only one letter in the genetic coding is amiss.
However, this is enough for a large part of the protein expressed by the gene to be missing. This change makes the inhibitor hyperactive, causing it to repress the activators for too long and extend the circadian cycle by at least half an hour.
Genetic mutation may cause sleep delays of 2 hours or more
Using a gene database search, the researchers found this mutation in 1 in 75 non-Finnish Europeans. Additionally, using questionnaires and interviews, the scientists studied the sleep patterns of six Turkish families and found 39 carriers of the CRY1 mutation.
Carriers of the genetic mutation fell asleep much later than their counterparts who did not carry the mutation, and some even had fractured sleep patterns. At around 4 a.m., non-carriers were approximately halfway through their sleep, whereas for carriers, this midpoint was delayed until between 6 a.m. and 8 a.m.
"Carriers of the mutation have longer days than the planet gives them, so they are essentially playing catch-up for their entire lives," says first author Alina Patke, a research associate in the laboratory of principal investigator Young.
"It is as if these people have perpetual jet lag, moving eastward every day," says Young. "In the morning, they are not ready for the next day to arrive."
However, the researchers note that the effects of this mutation can still be overridden with strict, self-enforced sleep routines.
"An external cycle and good sleep hygiene can help force a slow-running clock to accommodate a 24-hour day," says Patke, who identifies as a night owl herself. "We just have to work harder at it."