Those who struggle to get out of bed in the morning may be able to hold their genes responsible, new research suggests. Scientists have discovered that a person's waking habits are mirrored by body cells that are equipped with their own daily alarm clocks.

The work represents the first internal look at the biological clocks of those suffering from sleeping disorders, says study leader Steven A. Brown of the Institute for Pharmacology and Toxicology at the University of Zurich, Switzerland.

"One of the big surprises was that so much of our daily behaviour was genetically encoded," Brown says. "The idea that skin cells are telling us anything about our behaviour was, for me, quite fascinating."

The study investigated the circadian rhythm - the brain-controlled phenomenon that governs various body functions over a 24-hour period - of extreme late and early risers.

LARKS AND NIGHT OWLS

Suitable volunteers were recruited by the study team using TV advertisements shown between 3am and 4am.

"We got both our early types and our late types that way," Brown says. "Some had not yet gone to bed, while others were already up."

Skin cells taken from the volunteers were cultured in the lab and injected with a bioluminescence gene found in fireflies. According to the study, which appears in the online edition of the journal Proceedings of the National Academy of Sciences, these altered cells lit up or dimmed according to the individual's sleeping patterns.

Cells belonging to habitual larks had the shortest glowing periods, while those of the night owls had the longest, the study found. Brown likens the effect seen in late risers to that of someone keeping time with a slow wristwatch. "You end up being late for everything," he says. "Now imagine your watch was fast, meaning it had a time period of less than 24 hours. Then you'd be early for everything."

The study reveals that genes, not just environmental factors such as day length, have a major influence on our circadian clock, he says.

Russell Foster of the Nuffield Laboratory of Ophthalmology at the University of Oxford, England, was not involved in the research. "Knowing that skin clocks 'tick' in the same way as brain clocks provides a nice tool to address whether a person is likely to be an early or late riser," Foster says. "It's remarkable that measures from the skin can allow a prediction of brain-driven behaviour."

BRAIN LINK

"Human daily body rhythms are a complex, brain-related phenomenon," Brown says, "but it's directed by the same molecules that are present in your skin." These cells give an accurate picture of an individual's daily body clock by mirroring the molecular workings of the central clock in your brain, the lead researcher says. "By looking at slave clocks in the skin, we can get a better understanding of the way the [master] clock in the brain is working."

The research may lead to new treatments for people suffering from sleep disorders, the researchers say.

"Such treatments could potentially be used to reset a patient's 24-hour cycle to more sociable hours, so they wouldn't find themselves awake watching TV in the wee small hours." This would probably be done with drugs that target the circadian clock pathway, Brown says.

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