Late for work again? Some people have the opposite problem: on average, these morning larks fall asleep at 7:30 p.m. and wake up at 4:30 a.m. Their largely inherited and unusual sleeping patternone first discovered in 1999is called Familial Advanced Sleep Phase Disorder Syndrome, or FASPS. And by studing a large family with the condition, researchers from the University of Utah have uncovered the first human gene that controls circadian rhythmthe roughly 24-hour-long sleep-wake cycle of many animals.

Last week, Louis Ptacek, Ying-Hui Fu and others reported in Science Express, an online advance publication of Science articles, that most of the affected family members harbor a mutation in a gene called hPer2, a clock gene that helps regulate the circadian rhythm. Alterations of the equivalent gene in fruit flies or mice makes them, too, sleep and wake earlier than normal. The mutation in the hPer2 gene changes a single amino acid in the protein, meaning that another protein, a kinase, can no longer attach to it a regulatory phosphate group. This missing group probably leads to a more rapid accumulation of hPER2 protein in the cell and results in an advanced sleeping pattern. Of interest, a mutation in the kinase itself leads to a FASPS-like phenotype in golden hamsters.

One branch of family members in the study did not show a mutation in hPer2. But these individuals were, on average, also less extreme "morning larks" than their affected relatives. According to Ptacek, they probably carry other genetic variations that might be common in the general population. "There are plenty of morning larks" that go undetected, he says. Also, other families with FASPS do not have the hPer2 mutation, and studies of their DNA will probably reveal more genes involved in circadian rhythm control. Further down the line, genes might surface that make people sleep longer in the morning. The proteins encoded by these genes, scientists hope, could serve as drug targets to help people with transient sleeping problems that are the result of, say, jet lag or working nightshifts.