Society celebrates its early birds, but for an unlucky few, the internal alarm clock goes off much too early. Now, studies of early-rising mice have led researchers to change their view of how biological clocks tell time, and could ultimately lead to new treatments for people with sleep disorders. Variation in sleep cycles is normal, says Louis Ptácek, a geneticist at the University of California at San Francisco. “In the general population, there’s a huge spectrum between people who habitually wake up without an alarm clock or coffee at 6 am, and those who would sleep until two in the afternoon if they didn’t have any other responsibilities,” says Ptácek.
But at the far reaches of normal behaviour are individuals whose internal curfews are set much earlier or later than those of the rest of the population. People who have familial advanced sleep phase syndrome — which Ptácek estimates affects only 0.3% of the population — usually wake up around 4 in the morning, and go to bed around 7 at night. “The time that most people are most awake is around dinnertime,” says Ptácek. “But that’s when these people are so sleepy that their face could fall into a bowl of soup.”
Ptácek and his colleagues previously showed that some people with the condition carried a mutation in a gene called period 2 (PER2), and levels of PER2 proteins are often critically low.