Sleeping Really Strange Hours? Maybe a Rogue Gene is to Blame

American Academy of Neurology 2006 Sleep Science Award winner Ying Hui Fu and Howard Hughes Medical Institute investigator Louis Ptacek study mice, flies and families with rare sleep disorders to discover how molecules determine when we sleep. Photo by Majed.

by Jeffery Norris The earliest-rising morning larks and the most extreme night owls may have a reason to blame genes - sometimes just one gene -- for their being out of sync with the rest of us. Husband and wife research team Louis Ptacek and Ying Hui Fu, now at UCSF, identified a mutant gene from sleep-deprived members of one Utah family in which many of these rare birds roost. The mutated gene is all that is necessary to shift the gears within the biological clocks of affected family members, causing them to go to bed very early and to wake up very early, too. That was the first sleep-disorder-causing gene ever isolated. There will be more to come. Fu and Ptacek are hot on the trail of a mutant gene that causes a similar inheritance pattern in another family with the opposite problem - affected family members are driven to go to bed and wake up later and later. In all, the researchers now are tracking 60 families in which the inheritance patterns of sleep-phase disorders suggest that one or very few gene mutants may be responsible. Their research is shedding light on how molecular gears and springs work together inside cells to run our biological clocks. And although unwilled wee-small-hour wakefulness often disrupts the lives of those whose natural sleep times are outside the norm, Ptacek and Fu suggest that with a better understanding of sleep cycles comes hope on the horizon for relief in the form of new drug treatments. The work of researchers like Ptacek and Fu may eventually lead to new drugs to treat not just rare sleep-phase disorders, but also jet lag, insomnia, and a sleep-phase disorder that is common among older people that causes many to fall asleep and wake up earlier than they did when they were younger adults, and earlier than they would like. This phenomenon is known as advanced sleep phase syndrome -- ASPS. Even Bacteria Run by the Clock
Life on Earth evolved over billions of years of days and nights. Not so surprisingly, organisms ranging in complexity from bacteria to humans have adapted to differences between daytime and nighttime environments. Metabolic and physiological activity waxes and wanes in cycles that repeat roughly every 24 hours. Sleep is one of many biological events governed by these circadian rhythms. Sunlight or even strong electrical lights can reset the sleep clock to some degree. In addition, the timing of human sleep is shaped not just by biology, but also by our obligation to adapt to culturally determined schedules. But strip these factors away, and what remains is the natural circadian sleep pattern. Researchers have measured it in volunteers who stayed comfortably inside for weeks on end - in constant dim light, with no scheduled activities and without social stimulation or cues about time from the world outside. The average time between bedtimes turns out to be about 24.3 hours. Without cues from the sun or society, most people will go to bed a bit later each night. Ptacek and Fu's interest in sleep research began before they came to UCSF, at the University of Utah. A colleague, sleep neurologist, Christopher Jones, told them about a woman who complained of an inability to stay asleep in the morning or to stay awake through the evening. In the early morning hours she was driven to vacuuming and visiting all night food stores. The doctors she had visited told her she was depressed or antisocial, or that nothing was wrong. But the woman persisted in seeking help, in part because she discovered that her daughters and other family members had the same problem. When she saw Jones, he recognized a never-before-described, disabling sleep disorder. Family Trees
Fu and Ptacek already were experienced in tracking disease genes by looking at human pedigrees - essentially family trees with information about individual afflicted with particular diseases. Comparing the DNA of affected family members with the DNA of unaffected family members can lead to the identification of variant genes that are shared by those afflicted and that play a role in the disease. The researchers patiently gathered DNA and information from family members, starting with Jone's first patient. The woman agreed to an isolation experiment of the sort originally used to calculate the normal 24.3 hour human sleep cycle. The woman's own sleep cycle measured a full hour shorter -- 23.3 hours -- explaining why she was inclined to go to sleep and awaken so early. The researchers measured related circadian cycles in family members - including variations in EEG brain waves, melatonin and body temperature. These rhythms also were shorter in those with the disorder, which the researchers named FASPS -- for familial advanced sleep-phase syndrome. After more than a year of painstaking work, the researchers identified and cloned the mutant gene responsible for FASPS in the Utah family - the first time a gene was implicated in variations in human circadian rhythms. But extreme night owls and morning larks with single, rare gene mutations are at the fringes when one plots circadian rhythms. The population as a whole traces a normal bell curve distribution, according to Ptacek. Given a choice, there are many people who would rise at 7 o'clock, and many others who would rather sleep until 10. Unlike the extreme cases, Ptacek thinks these normal variations are due not to rare mutants, but rather to more frequently occurring variants in several different genes that are circulating among the broader population. "There's no proof that this variability has been selected for," Ptacek says, "But you could make an argument that from an evolutionary perspective, it makes sense to have individuals in the group awake at different times -- to better watch out for threats from wild animals." Running Mice, Flying Flies
"Everything we have done starts with human families with disease," Ptacek says. But once a disease gene is identified in humans, much more can be learned in animal experiments. Over the past three decades researchers have identified about 10 of these "clock" genes in fruit flies, and counterparts in mice and humans. By testing normal and mutated sleep-phase genes and proteins in lab mice and flies, Ptacek and Fu are learning more about how they function as the gears in the biochemical mechanisms that determine when we sleep. The mice and flies live in tightly controlled light conditions. The researchers employ sensors to keep track of when the mice are active in their cages and flies are flying in their vials. When they sleep, no sensors are activated. Fu and Ptacek inserted the mutant human gene responsible for FASPS -- called hPer2 -- into mice and fruit flies. The human gene worked, leading to the manufacture of the encoded mutant protein and to a shift in sleep cycles. Phosphate Molecules are Small Change, Greasing the Palms of Enzymes
It turns out that hPer2 encodes a protein that is part a chain reaction triggered by phosphate molecules being added or removed from enzymes - the proteins that drive biochemical actions in cells. One enzyme adds a phosphate to another enzyme, thereby activating it, and so on down the line. Activation of enzymes by phosphorylation is a common way of regulating cellular activities. The pace at which certain specialized proteins gain or lose phosphates may set the timing for circadian clocks, Ptacek suggests. The altered protein encoded by the mutant gene first identified by Fu and Ptacek attaches less efficiently to the enzyme that phosphorylates it. Phosphorylating enzymes are called kinases, and the sleep researchers have teamed with UCSF chemist and kinase expert Kevan Shokat to learn more about the identities and biochemical roles of genes and proteins governing circadian sleep cycles. Another goal is to identify which among the biochemical players might best be targeted to relieve specific sleep disorders. An optimistic Ptacek explains, "These are enzymes, and enzymes are druggable targets."