Mutation in clock gene explains why some night owls stay up late

A gene variant may explain why some people prefer to stay up late and hate early mornings.

The variant is a mutated form of the CRY1 gene, known to play a role in the circadian clock. Michael Young, at The Rockerfeller University, New York, and his team discovered the mutation in a person diagnosed with delayed sleep phase disorder – a condition that describes many so-called “night-owls”.

The team found that five of this person’s relatives also had this mutation, all of whom had a history of sleep problems. They then studied six families in Turkey whose members included 39 carriers of the CRY1 variant. The sleep periods of those with the mutation was shifted by 2 to 4 hours, and some had broken, irregular sleep patterns.

The mutation seems to slow the body’s internal biological clock, causing people to have a longer circadian cycle and making them stay awake later. The team have calculated that the variant may be present in as many as one in 75 people in some populations, such as Europeans of non-Finnish descent.

But those who have a longer circadian cycle need not despair. Young says many people with delayed sleep phase disorder are able to control their sleep cycles by sticking to strict schedules. “It’s a bit like cigarette smoking in that there are things we can do to help the problem before turning to drugs,” he says.