A mutant gene rather than anti social tendencies may be the cause of people going to sleep and waking up unsociably early, scientists said on Wednesday.
They made their discovery after studying three generations of a family in which five members suffered from the so-called earlybird ailment officially known as Familial Advanced Sleep Phase Syndrome.
"These results show that the gene is a central component of the mammalian circadian clock," the researchers from the Universities of California and the Howard Hughes Medical Institute wrote in the science journal Nature.
They identified the mutant gene as CKIdelta.
People with earlybird syndrome sleep for the same length of time as non-sufferers but typically are wide-awake and raring to go long before everyone else is up and about.
For many, it is a bonus rather than a millstone as they can use the time to get things done without daylight distractions.
But for others, living a life out of synch with their neighbors is a heavy anti-social burden.
"Some of them would never come to a doctor because they aren't troubled by it," Howard Hughes researcher Louis Ptacek said. "Often they have adjusted and accommodated their jobs to match their ability."
"But others are bothered by being out of phase with the rest of the world," he added.
The researchers said transferring the mutant gene to mice replicated the human experience but, oddly, inserting it into fruit flies made them sleep longer.
They said further research into the role of the gene in regulating the human body clock could have major implications for the development of novel compounds for the treatment of sleep disorders.