Delayed phase jumps of sleep onset in a patient with non-24-hour sleep-wake syndrome

We studied a 30-year-old man with non-24-hour sleep-wake syndrome. To investigate the relationship between environmental light-dark cycles and his sleep-wake rhythm, we documented his sleep log and rectal temperature data without any therapeutic interventions. We found that 1) the patient's sleep-wake pattern consisted of two different components, appearing alternatively, with a period of 27.2 days: regular free-run (R free-run), consisting of a daily 30- to 60-minute regular delay of sleep onset; and jumping free-run (J free-run), with clusters of delayed (> 4 hours) phase jumps in sleep onset (DP jump): 2) the frequency of sleep onset was higher during late evening hours to midnight hours than in the daytime; 3) DP jumps occurred exclusively when the prior sleep onset was delayed into the daytime; and 4) a cluster of DP jumps was likely to start when the patient's low temperature zone (a period in which rectal temperature was below average) at subjective night was illuminated by sunlight. These results suggest that DP jumps in the patient may occur due to illumination of the delay portion of the phase-response curve.