For those who can never understand those joyful early birds, people who seem to rise cheerfully from their beds well before dawn, while you try not to demolish your alarm clock, it is just their genes working.
Scientists led by Dr. Louis J. Ptacek, a professor of neurology at the University of California, San Francisco have discovered the modus operandi of Per2 (Period2) the gene mutation responsible for this phenomenon.
This genetic alteration had already been identified through a research involving a family of early risers, in Utah, US, in 2003.
The condition of going to bed and rising very early is dubbed as familial advanced sleep phase syndrome (FASPS).
Scientists now, publishing their result in the journal Cell, have identified how the gene mutation causes this condition.
According to them, replacement of one amino acid from among hundreds found in a protein can result in irregular sleep patterns.
Ptacek's group has determined how the gene causes the condition, by transplanting the gene into mice to create rodents with FASPS.
"They get up and start running on their running wheels four to six hours before other mice, and they also stop running on their running wheels four to six hours earlier than normal mice', says Ptacek.
The scientists hope the results could pave the way for future therapies aimed at seasonal affective disorder, jet lag and insomnia.