Non-24-Hour Sleep-Wake Disorder
NORD gratefully acknowledges James S.P. Fadden, MA, Vice-President, Circadian Sleep Disorders Network, and Katherine Sharkey, MD, PhD, Assistant Professor of Medicine, Rhode Island Hospital/Alpert Medical School of Brown University, Departments of Medicine and Psychiatry and Human Behavior, for assistance in the preparation of this report.
Synonyms of Non-24-Hour Sleep-Wake Disorder
circadian rhythm sleep disorder, free-running type
- free-running disorder
- hypernychthemeral syndrome
- non-24-hour disorder
- non-24-hour sleep-wake cycle disorder
- non-24-hour sleep-wake syndrome
Non-24-hour sleep-wake disorder (N24) is a circadian rhythm sleep disorder in which an individual's biological clock fails to synchronize to a 24-hour day. Instead of sleeping at roughly the same time every day, someone with N24 will typically find their sleep time gradually delaying by minutes to hours every day. They will sleep at later and later clock times until their sleep periods go all the way around the clock. (In extremely rare cases the sleep rhythm will gradually advance rather than delay.) Patients' cycles of body temperature and hormone rhythms also follow a non-24-hour rhythm. Attempts to fight against this internal rhythm and sleep on a normal schedule result in severe and cumulative sleep deprivation.
N24 occurs in roughly 50% of completely blind people but also occurs in an unknown number of sighted people.