DALLAS, Dec. 29 (UPI) -- Researchers have identified a series of inherited genes for sleep, wake and activity cycles that are linked to the development of bipolar disorder, which they said could aid in the development of new methods for prevention and treatment.
Although bipolar disorder has both environmental and genetic causes, circadian rhythms -- the body's natural sleep, wake and activity cycles -- can precede mood shifts and play a role in the disorder.
"We were able to identify 13 sleep and activity measures, most of which are inherited, that correlated with whether an individual had bipolar disorder. In addition, we were able to trace some of these traits to a specific chromosome," said Dr. Joseph Takahashi, chairman of the neuroscience department at the University of Texas Southwestern Medical Campus, in a press release.
Researchers in the study, published in the Proceedings of the National Academy of Sciences, analyzed genetic and medical data for 558 members of 26 Costa Rican and Colombian families, 136 of whom were diagnosed bipolar and 422 who were healthy.
Among participants, the researchers identified 73 phenotypes among the family members, 49 of which were significantly heritable, and 13 of which were significantly associated with bipolar disorder. The 13 phenotypes associated with the disease were: mean of awake duration, amplitude, Hill acrophase, interdaily stability, interdaily variability, median activity, relative amplitude, mean length of sleep bouts during sleep period, mean number of sleep bouts during awake period, time of sleep offset, time of sleep onset, meant total minutes scored awake, and total minutes in awake bouts after sleep onset.
Researchers found those with bipolar disorder slept longer, spent fewer minutes awake overall, were active for shorter periods of time and displayed overall lower levels of activity.
"This study represents a key step in identifying the genetic roots of this disorder and, in turn, providing targets for new approaches to preventing and treating bipolar disorder," said Dr. Nelson Freimer, who directs the Center for Neurobehavioral Genetics at the University of California Los Angeles.