title: Circadian rhythmicity in emerging mood disorders: state or trait marker?
abstract: BACKGROUND
  Circadian rhythm disturbances overlap with the symptoms of mood episodes and may trigger or prolong mood symptoms. There is limited research on the role of circadian disturbances in mood disorders in young people and/or first episode cases of unipolar and bipolar disorders.
  
  
  METHODS
  Actigraphy was undertaken for about 14 days in 63 post-pubertal individuals aged 13-25 years with a recent onset of a mood disorder meeting recognised diagnostic criteria. We examined associations between three easily interpretable markers of circadian rhythm activity (amplitude, acrophase and rhythmicity index) and demography and clinical characteristics. Then, circadian markers were compared between diagnostic groups, controlling for potential confounders.
  
  
  RESULTS
  Longer duration of illness was correlated with reduced circadian rhythmicity and lower levels of activity over 24 h. A delay in the timing of maximum activity was associated with the level of manic but not depressive symptoms. The circadian rhythmicity index differentiated unipolar from bipolar cases, and in bipolar but not unipolar disorder, the rhythmicity was less robust in those with more severe manic or depressive symptoms.
  
  
  CONCLUSIONS
  Less robust circadian rhythmicity, especially associated with increasing symptom severity, may represent a more specific or a trait marker of young people with mood disorders who are at higher risk of a bipolar course of illness.
authors.affiliation: Brain and Mind Centre, The University of Sydney, Sydney, Australia. ashlee.hannon@sydney.edu.au.
authors.forename: Ashlee B
authors.initials: AB
authors.lastname: Grierson
authors.affiliation: Brain and Mind Centre, The University of Sydney, Sydney, Australia. ian.hickie@sydney.edu.au.
authors.forename: Ian B
authors.initials: IB
authors.lastname: Hickie
authors.affiliation: Charles Perkins Centre, Brain and Mind Centre, The University of Sydney, Sydney, Australia. sharon.naismith@sydney.edu.au.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Naismith
authors.affiliation: Brain and Mind Centre, The University of Sydney, Sydney, Australia. daniel.hermens@sydney.edu.au.
authors.forename: Daniel F
authors.initials: DF
authors.lastname: Hermens
authors.affiliation: Notre Dame University, Sydney, Australia. e.scott@sydney.edu.au.|Sydney Medical School and Brain and Mind Centre, The University of Sydney, Sydney, Australia. e.scott@sydney.edu.au.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Scott
authors.affiliation: Academic Psychiatry, Institute of Neuroscience, Newcastle University, Newcastle, UK. jan.scott@newcastle.ac.uk.
authors.forename: Jan
authors.initials: J
authors.lastname: Scott
keywords: Adolescence; Bipolar; Circadian rhythm; Trait; Unipolar; Young adult