Narrator: This is Science Today. Whether you're a morning person or a night owl, we all have our own internal body clock, or circadian rhythm. This 24-hour cycle regulates a variety of biological processes, including sleep. Now, a University of California, San Francisco study offers new insight into this cycle. Ying-hui Fu led a study that identified a gene and mutation that causes a rare sleep behavior called Familial Advanced Sleep Phase Syndrome.

Fu: The main problem they have is they like to go to bed really early, like 4PM, 6PM and they like to get up very early, like 2AM, 4AM, 5AM.

Narrator: While this syndrome is rare, Fu says their study reveals that sleep behavior is genetically determined and the effects of the human circadian rhythm are far-reaching.

Fu: If you think of the circadian rhythm as a center, you can connect sleep, connect to depression, connect to learning and memory and then come back to migraine headache and then it connects to asthma, so it's very broad.

Narrator: For Science Today, I'm Larissa Branin.