Poor compensatory function for sleep loss as a pathogenic factor in patients with delayed sleep phase syndrome

Delayed sleep phase syndrome (DSPS) is a condition in which the patient is unable to reset or phase-advance his/her sleep timing properly after transient sleep delay and consequently shows persistent sleep phase delay. Prior studies suggested that DSPS is associated with a phase delay in the circadian pacemaker, but there was no evidence to explain the patient's inability to reset sleep phase.

We used an ultra-short sleep-wake schedule together with simultaneous measurement of dim light melatonin rhythm after 24-hour sleep deprivation to allow the differential observation of diurnal sleep propensity fluctuation both from circadian and homeostatic aspects in 11 patients with DSPS (17-37 years; 8 men, 3 women) and 15 healthy controls (19-32 years; 8 men, 7 women).

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DSPS patients showed less ability to compensate for previous sleep loss during their circadian day and first hours of their circadian nighttime determined by dim light melatonin onset compared with controls, while controls compensated for previous sleep loss at most circadian times. Though shapes of dim light melatonin rhythm did not differ between the groups, phase angle between melatonin and sleep propensity rhythms was wider in DSPS patients than in controls.

These findings suggest that poor compensatory function for sleep loss predisposes DSPS patients to failure to reset their sleep phase. Our results provide implications for understanding not only the pathophysiology of DSPS but also the biological basis for why some people can change their sleep schedule easily according to personal or social demands while others cannot.