It's not your fault, night owls.
If you can't get to sleep at a reasonable hour and dread your alarm clock going off each morning, it could be something in your genes.
Researchers at Rockefeller University in New York have found that a variant in the gene CRY1 slows the internal clock that determines when you feel sleepy.
Those who have the so-called night owl variant of this gene have longer circadian cycles, meaning they stay awake later at night, according to the study published in the journal Cell on April 6.
This mutation may be present in as many as one in 75 people in some populations.
"The only genetic variations in humans that have been described before to cause changes in sleep timing have been extremely rare to the point that it probably only affects single families, so the one that we reported now is a lot more common than that," said Dr. Alinke Patke, lead author of the study and the research associate who found the variant.
Delayed sleep cycle
People who identify as night owls are often diagnosed with delayed sleep phase disorder (DSPD), which makes them energetic long after most people have hit the pillow.
When she found the sequencing trace, Patke was working with Dr. Michael Young, head of Rockefeller's laboratory of genetics — which has been studying the circadian clock for more than three decades — as well as sleep researchers from Weill Cornell Medical College in New York.
Together they were studying patients who had agreed to spend two weeks in a laboratory apartment isolated from all signs of the time of day, sleeping and eating whenever they chose.
Researchers observed sleep behaviour and collected skin cells from each participant.
While most people follow a 24-hour cycle between sleep and wakefulness, one study subject who had been diagnosed with DSPD was found to have a cycle that was 30 minutes longer.
In this patient, changes in the hormones that affect the circadian clock — including melatonin, which helps to regulate sleep — also were delayed.
In most people, melatonin rises between 8 p.m. and 10 p.m., but in this subject's case, melatonin levels rose "much, much later" — around 2 or 3 a.m., said Patke.
The researchers then found that five relatives of the patient had the same mutation.
The team expanded its research to larger genetic databases from around the world. A collaborator in Turkey helped identify unrelated families whose members carry the CRY1 mutation, confirming their altered sleep patterns through interviews and questionnaires.
Through this and other database research, the researchers determined that as many as one in 75 people of non-Finnish European descent have the mutation. (A 2016 study published in the journal Nature determined that Finns do not descend from other Europeans.)
It's a lark's world
Left to their own devices, people who have DSPD but no additional sleep disorders would get a healthy amount of sleep.
The trouble is that most people with DSPD must get to work or school at a time that requires them to wake before their bodies have had enough sleep.
"If you work early in the morning then you're considered more productive. It's obviously not true, just because you start later if you also work later the hours you spend are obviously the same," said Patke. "It's a misconception, but for anyone who doesn't have this morning rhythm, it can be quite a burden."
As it happens, Patke describes herself as a night owl, but she tested negative for the variation.
The Centers for Disease Control and Prevention estimate that between 50 and 70 million adults suffer from a sleep or wakefulness disorder in the United States alone. Chronic sleep conditions can predispose individuals to a number of other health problems, including obesity, diabetes and depression.
The researchers note that there's no approved medical test for the variation, and no treatment associated with it if there were. However, they can be contacted about opportunities for participation in followup sleep studies at firstname.lastname@example.org and email@example.com.