Doing night shifts may not be everyone’s cup of tea. Or, for that matter, staying up for the World Cup matches if there is office to attend the next day. But if they do stay awake the night, they could be putting themselves and others at great risk, say British scientists who probed the genes of people who find it hard to fight off sleep deprivation.

A team of researchers at University of Surrey’s Sleep Research Centre found that a sizeable section of the population has a peculiar variation in the biological clock gene called PERIOD3, which makes it difficult for them to discharge their duties early in the morning if they haven’t slept well.

The gene has two variants, which produce either a long or short protein variant. Those carrying only copies of the gene that expresses the long version of the protein struggle to stay awake, the Surrey scientists reported in Current Biology. The problem was more pronounced during the early hours — between 4 and 8 am, they said.

While it is difficult to assess what percentage of the Indian population carries the PERIOD3 gene that encodes for the long variant protein, the scientists have estimated that 10 per cent of the UK population has the two copies of the gene.

If this is extrapolated to India, about one-tenth of pilots, truck and engine drivers, those manning railway signal posts and call centres employees handling sensitive financial data may fall in this category.

To understand whether this gene is involved in attention deficiency, the team — consisting of biologists and psychologists — compared how individuals with only the long variant and those with only the short one coped with being kept awake for two days and the intervening night. “The differences between the individuals were striking. Some participants were experiencing no problem staying awake while others were really struggling,” said Antioine Viola, a co-author of the study.

Individuals with the longer variant of the gene performed poorly on tests for attention and working memory during the early morning hours. “This is exactly the time of night when shift workers struggle to stay awake and many sleepiness-related accidents occur,” said Derk-Jan Dijk, leader of the team. Dijk, however, cautioned that the research was conducted in the lab and they didn’t know yet how it would apply to the real world.

Manvir Bhatia, head of sleep medicine at Sir Ganga Ram Hospital, New Delhi, said that many people who complain of insomnia may not actually be suffering from it but from “delayed sleep-phase syndrome.” “People with this disorder tend to sleep late and wake up late. But when they are forced to carry out any task during the time they should be sleeping, chances are that there could be delays in decision making. In many situations, such delays could be fatal,” observed Bhatia.