Background
Episodic bipolar and unipolar mood disorders are characterized by disruptions in sleep-wake cycle, patterns of physical activity and circadian rhythms. These phenomena are most evident in those who experience recurrent mania or ‘atypical’ depressive episodes. As 75% of major mental disorders emerge before age 25 years, the focus on recording the earliest features of these disorders in teenagers and young adults
Methods
We have investigated sleep-wake cycle, physical activity and circadian features in young persons with emerging mood disorders in two large clinical samples (n=307, 30% bipolar-type, mean age = 19 years; n=1797, 16% bipolar-type, mean age = 18 years). Additionally, we are investigating phenotypic and circadian features in a longitudinal study of adolescent twins (n=2459, mean age=16 years). Measures include objective and prolonged actigraphic-derived assessments of 24-hour sleep-wake cycles and daytime physical activity, early evening melatonin secretion patterns and relevant metabolic function parameters in selected sub-groups.
Results
In clinical samples, there is evidence of delayed onset and offset of sleep-wake cycles, reduced day-time physical activity and disrupted onset of night-time melatonin release in up to half of young persons with emerging mood disorders. These features are more pronounced in those with more severe conditions and those with a history of mania or hypomania episodes. In twins, sleep-wake cycle phenotypes are predicted by shared genetic characteristics and appear to have their own longitudinal associations with the ‘atypical’ as distinct from more classical ‘anxious depression’ illness-type. Additionally, hypomanic-type features are extremely common in young people, with about one-in-five reporting at least one episode of sleep disturbance and activitation prior to age 25 years.
Conclusion
Delayed sleep offset and disrupted circadian function are characteristics of a major subgroup of young people with emerging mood disorders. While under strong genetic control, these features are exacerbated by other environmental and illness-related factors. These studies provide unique data concerning relationships between circadian factors and the onset and course of depression, and other comorbidities, in young persons during the early phases of illness. Circadian systems may represent a key target for behavioural or pharmacological treatments of depression independent of other illness characteristics.