Melatonin rhythms in delayed sleep phase syndrome

The aim of this study was to compare circadian and sleep characteristics be tween patients with delayed sleep phase syndrome (DSPS) and healthy control s. The authors studied 8 DSPS patients and 15 normal controls. Serum melato nin concentration was assessed every hour for 24 h under dim light conditio ns. The sleep phase and the melatonin rhythm in DSPS patients were signific antly delayed compared to those in normal controls. Sleep length was signif icantly greater in DSPS patients compared to that in controls, but the dura tion of melatonin secretion did not differ between the two groups. The fina l awakening, relative to melatonin onset, melatonin midpoint, and melatonin offset, was significantly longer in DSPS patients than in controls. By con trast, the timing of sleep onset relative to melatonin rhythm did not diffe r between the two groups. The authors found a significant positive correlat ion between sleep phase markers and melatonin phase markers in DSPS. They p ostulate that a delayed circadian pacemaker may be responsible for delayed sleep phase syndrome. The alteration of phase angle between melatonin rhyth m and sleep phase suggested that not only the delay of the circadian clock but also a functional disturbance of the sleep-wake mechanism underlies DSP S.