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.