Researchers in the US have identified a gene mutation that causes a person's internal body clock to run slowly, leading to delayed sleep and difficulty in waking early.
'Carriers of the mutation have longer days than the planet gives them, so they are essentially playing catch-up for their entire lives,' said lead author Alina Patke, from The Rockefeller University in New York.
The circadian clock is controlled by a balance of proteins called activators and inhibitors, which build up and wane over the period of the clock's cycle. The activators that are present at the start the cycle produce inhibitors over the course of the day, which in turn suppress these activators returning the cycle to the beginning. The cycle restarts once the inhibitors eventually run out, leaving the activators to build up again.
This mutation, on the gene CRY1, is present in one of the inhibitor proteins, causing it to become overactive and prolonging the period in which the activators are suppressed, therefore extending the length of day.
'It's as if these people have perpetual jet lag, moving eastward every day,' said Dr Michael Young, co-author and principal investigator of the study. 'In the morning, they're not ready for the next day to arrive.'
The study, published in Cell, used skin cells from a patient diagnosed with DSPD to locate the mutation. The researchers subsequently found that five of the patient's family members were carriers and had also experienced abnormal sleep.
DSPD is characterised by the delayed onset and fragmented sleep and has been shown to affect up to 10 percent of the population. Sleep disorders, including DSPD, have also been associated with other illnesses, such as anxiety, depression and diabetes.
The researchers say that not all cases of DSPD can be attributed to the mutation on the CRY1 gene, however, but they estimate that this variant could be present in as many as one in 75 people in some populations.
'Our variant has an effect on a large fraction of the population,' Patke said. However, as circadian rhythms also respond to external cues such as light levels, carriers of this mutation can help themselves restore a normal sleep-wake cycle.
'An external cycle and good sleep hygiene can help force a slow-running clock to accommodate a 24-hour day,' said Patke, who says that she is herself a 'night-owl' but does not carry the mutation. 'We just have to work harder at maintaining a normal cycle,' she said.