Early-to-sleep, early-towake rhythm may not be as extremely rare as has long been believed. In a new study in the journal Sleep by researchers in San Francisco , Salt Lake City and Madison, of more than 2,400 patients who visited a sleep clinic for complaints, a small number of them were found to have a previously unrecognised familial form of advanced sleep phase, a kind of permanent jet lag that the study showed often runs in families.
The lead author of the study, Louis J Ptacek, professor of neurology at the University of California, San Francisco, said the world is full of long and short sleepers — the so-called owls who stay up late and get up late, and the larks who go to sleep early and wake up early. These patterns, too, often run in families, and Ptacek and his colleagues have been identifying genes that influence them.
Such natural long and short sleep patterns fit into the normal distribution of people’s sleep needs. But those with an abnormally advanced or delayed sleep phase are different — they may need the same amount of sleep as the average person, but the times at which they need to sleep and wake are anything but average. Advanced sleep phase is now known to be determined by a single dominant mutation in a growing list of genes discovered in the laboratories of Ptacek and his collaborator Ying-Hui Fu .
“But while this mutated gene travels in families, its expression can vary based on what the rest of the genome looks like,” Ptacek said. He and his colleagues concluded that “extreme morning chronotypes,” as people with advanced sleep phase are called, “are not exceedingly rare.” Their analysis showed that among visitors to a sleep clinic, some 3 in 1,000 have advanced sleep phase, and in two-thirds of those people, the pattern is familial.
Chances are, too, there are far more extreme larks than come to professional attention. The team pointed out that people with advanced sleep phase rarely consult sleep doctors or are studied in sleep clinics because most of those affected seem to like the pattern, perhaps because it fits well into the rhythm of their lives or they have selected or created a rhythm that fits into their sleep-wake needs.
The incidence of advanced sleep phase disorder is likely underestimated because it results in fewer social conflicts. People are not usually penalized for getting to school or work too early. Night owls, on the other hand, are more inclined to seek the help of a sleep specialist because it’s so hard for them to get up and get going in the morning to meet the demands of school, work or household.
“People with delayed sleep phase often suffer a great deal,” Ptacek said. “They may be unable to fall asleep before 2, 3 or 4 am and then have to get up at 7. They tend to be chronically sleep-deprived and may not function well.”