Are you a night owl and have trouble getting up in the morning? It may be because your internal clock is genetically programmed to run slowly, researchers have found.

The findings showed that a mutation in a gene called CRY1 alters the human circadian clock, which dictates rhythmic behaviour such as sleep/wake cycles.  People who are carriers of the gene variant experienced nighttime sleep delays of 2-2.5 hours compared to non-carriers, the researchers reported in the journal Cell."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 City, US.

Night owls are often diagnosed at sleep clinics with delayed sleep phase disorder (DSPD) -- where a person's circadian ryhthm is delayed from the typical day/night cycle.

Mutation in CRY1 led to the development of DSPD, which affects up to 10 per cent of the population, according to clinical studies. People with DSPD often struggle to fall asleep at night, and sometimes sleep comes so late that it fractures into a series of long naps.  People with DSPD also have trouble conforming to societal expectations and morning work schedules, which leads to anxiety, depression, cardiovascular disease, and diabetes.  The gene mutation was discovered while studying the skin cells of people with DSPD.  The circadian clock responds to external environmental cues, so it is possible for people to manage the effects of the mutation on sleep.  "An external cycle and good sleep hygiene can help force a slow-running clock to accommodate a 24-hour day," Patke said.