Novel insights from genetic and molecular characterization of the human clock

Biological rhythms govern the ebb and flow of life on planet Earth. Animals have an internal timekeeping mechanism that precisely regulates 24-hour rhythms of body function and behavior and synchronizes them to the day/night cycle. Circadian pacemakers trigger behavioral and physiological processes that dictate our daily rhythms. Despite the importance of the circadian clock to all aspects of our physiology and behavior, the opportunity to probe the human circadian clock only recently became possible with the recognition of Mendelian circadian variants in people (familial advanced sleep phase syndrome, FASPS). We have now cloned several genes and identified mutations causing FASPS. Study of these genes and the proteins they encode and engineering of the human mutations into mouse models are allowing study of this fascinating phenotype and yielding novel insights into circadian regulation in humans. Ultimately, such work will allow us to understand the similarities and differences between the human clock and those of model organisms. In addition, recent studies have also linked disruption of the circadian clock with numerous ailments, including cancer, cardiovascular diseases, asthma, and learning disorders. Thus, studying the molecular mechanism of human circadian rhythmicity will have an enormous impact on our understanding of human health and disease. It should also lead to new strategies for pharmacological manipulation of the human clock to improve the treatment of jet lag, various clock-related sleep and psychiatric disorders, and other human diseases.