Do you party all night long, up until dawn?

Or are you a lark that falls asleep as soon as the sun sets?

Many believe that this is linked to the way of life, but a new research points out that this and how well people perform at tests after being deprived of sleep is rather a genetic trait than a habit.

After a whole night of staying awake, individuals possessing a long allele (gene variant) of the PER3 gene scored only half as well on cognitive tests as those with a short allele.

The most important differences in performance were detected during the small hours, when most tiredness-related accidents happen and shift-workers have most trouble staying awake. "It may be there are people who are genetically predisposed against shift work," said Malcolm von Schantz, at the University of Surrey, UK.

The researchers do not want this discovery to be used like a discriminatory tool against such individuals. "It is very possible that carriers of the long PER3 gene have advantages at other times," he notes.

The team selected 12 subjects carrying two copies of the long allele of PER3 and another 12 with two copies of the short allele. Participants' sleep patterns and brain activity (by electroencephalography) were monitored. Even if both types of individuals slept for about the same amount of time, those with the short PER3 gene spent roughly 15% of it in deep restorative sleep (slow-wave sleep) compared to 22 % for those possessing the long PER3.

The subjects remain in bed after waking up following the first night of sleep in the lab, in an environment with steady light and temperature levels, so that they didn't know what time it was (clocks were absent, of course).

During the next 40 hours the volunteers stayed awake and periodically performed cognitive tests (like word memory games on a laptop).

In the first 18 hours the tests' results were similar, but after being awake for 24 consecutive hours, the individuals with long PER3 scored only 50% of the results of those with the short allele.

Thus, even if individuals with long PER3 allele experienced deeper sleep, in fact they were more severely affected by the lack of sleep.

In the UK, about 10% of people present two copies of the long version of PER3 and 45% of the population has two copies of the short PER3 gene, whilst the remaining 45% are a mix (they carry one short allele and one long allele).

A previous research on 500 individuals discovered that the long version induced "larks" behavior (individuals that go to bed early) while the short allele depicts "owls" (persons that typically stay up late). The protein encoded by PER3 activates other genes, but its precise role is still unknown.