Study objectives: The objective of this study was to clarify the clinical features of sighted patients with non-24-hour sleep-wake syndrome.

Design: Clinical analyses of consecutive patients suffering from non-24-hour sleep-wake syndrome.

Setting: The sleep disorders clinic at Kohnodai Hospital, National Center of Neurology and Psychiatry, Japan.

Patients: Fifty-seven patients who were diagnosed consecutively as having non-24-hour sleep-wake syndrome between 1991 and 2001 were included in the study.

Measurements and results: The clinical features and sleep characteristics of the patients were analyzed. A semistructured psychiatric interview that included the criteria for Axis I or II disorders of Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised was conducted, and relationships between psychiatric problems and non-24-hour sleep-wake syndrome were analyzed. The patient cohort included 41 (72%) men and 16 (28%) women. The onset of non-24-hour sleep-wake syndrome had occurred during the teenage years in 63% of the cohort, and the mean ( +/-SD) period of the sleep-wake cycle was 24.9 +/- 0.4 hours (range 24.4-26.5 hours). The mean sleep length of the patients was 9.3 +/- 1.3 hours, and 44% of them had a sleep length of between 9 and 10 hours. Psychiatric disorders had preceded the onset of non-24-hour sleep-wake syndrome in 16 patients (28%); of the remaining 41 patients, 14 (34%) developed major depression after the onset of non-24-hour sleep-wake syndrome.

Conclusions: These results represent the first detailed clinical review of a relatively large number of sighted patients with non-24-hour sleep-wake syndrome.