Gene may determine sleep needs

Scientists have discovered a gene that may determine whether we are capable of sleeping for a little as three or four hours a night without suffering any ill effects.

The find could explain why the ability to remain awake happily for half the night appears to run in some families who may carry a genetic mutation that disrupts normal sleeping patterns.

Researchers hope that the discovery could open the way to understanding the chemical basis of sleep so that new drugs could be developed to help to overcome the effects of prolonged sleep disruption.

A study has found that the gene in question controls biochemical "channels" that determine the flow of charged particles - potassium ions - into the critical regions of the brain involved in sleep.

Scientists from the University of Wisconsin in Madison believe that they have for the first time showed how a single gene can affect the complex chemistry of sleep.

"This research offers the possibility of developing a new class of compounds that could affect potassium channels in the brain rather than the brain chemical systems targeted currently," said Chiara Cirelli, a professor of psychiatry at Wisconsin and the lead author of the study. The four-year study, published in the journal Nature, involved screening some 9,000 mutant fruit flies to see how genetic mutations affect sleeping patterns in the insects.

Like humans, fruit flies need between six and twelve hours of sleep each night and show signs of physical stress if they are deprived of rest. However, some flies carrying a mutation in a gene called "shaker" were apparently happy with just a few hours sleep.

When the short-sleeping flies were put through a series of tests, they performed as well as normal flies even though they slept for just a third of the time of the other flies. The scientists believe the findings are directly relevant to humans.

"The more behaviours we look at, in terms of sleep, the more we find that sleep in fruit flies is very, very similar to sleep in mammals," Professor Cirelli said.

Like humans, sleep-deprived flies need to catch up on their sleep to get back to normal and young flies need more sleep than older flies, which like humans suffer increasingly from sleep disruption the older they become.

The scientists believe that the shaker gene in fruit flies, and its equivalent in humans, controls the potassium channels that determine whether the body drifts into the deep sleep associated with slow brain waves - as opposed to the light, fast-wave sleep when there is rapid eye-movement (REM) and dreaming.

A detailed analysis of the mutation revealed that it prevented potassium ions from passing freely through the channels in the membrane of nerve cells in the brain.

"Humans have the same kind of genes and potassium channels. And we know that slow-waves must be generated by changes in the excitability of [brain] cell membranes," Professor Cirelli said.

"Our hypothesis is that if you don't have potassium channels, you won't get slow waves. The cell membrane will remain activated, preventing long periods of deep, non-REM sleep," she said.

The researchers write: "Most of us sleep 7-8 hours per night, and if we are deprived of sleep our performance suffers greatly; however, a few do well with just 3-4 hours of sleep, a trait that seems to run in families. Determining which genes underlie this [trait] could shed light on the mechanisms and functions of sleep."

- INDEPENDENT