Genetic liability to sleep traits and bipolar disorder subtypes

Sleep problems are common in people who have bipolar disorder, but recent research suggests sleep plays a different role depending on which type of bipolar disorder a person has (i.e. bipolar type 1 or type 2). We therefore investigated whether people with different bipolar disorder subtypes differed in their genetic risk for different sleep characteristics. These sleep characteristics were:

  • insomnia (difficulty sleeping)
  • sleep duration (number of hours slept each night)
  • excessive daytime sleepiness
  • chronotype (being a “morning person” or an “evening person”)

In the study, we analysed genetic data from 4672 BDRN participants who have bipolar disorder and 5714 control participants. Many BDRN participants will probably remember us asking them lots of questions about sleep patterns, and many kindly completed questionnaires about sleep and morningness/eveningness. Thank you to everyone who contributed.

We found that people with bipolar I disorder had significantly greater genetic risk for longer sleep duration, whereas people with bipolar II disorder had significantly greater genetic risk for insomnia. We did not find differences for daytime sleepiness or chronotype.

Our results suggest that clinical trials of sleep interventions in bipolar disorder should consider the role of bipolar subtypes and genetic risk for sleep disorders.  Future work will explore what factors could explain the differences in genetic risk for sleep traits we observed between people with different bipolar subtypes. The study was recently published in the journal JAMA Psychiatry (volume 77(3), pages 303-310).