Non-24-h sleep-wake disorder (free-running type, nonentrained type, hypernychthemeral syndrome) in sighted and blind patients

S W Lockley, M Uchiyama

Research output: Chapter in Book/Report/Conference proceedingEncyclopaedia / Dictionary EntryOtherpeer-review


Non-24-h sleep–wake Disorder (N24HSWD) is a cyclic debilitating circadian rhythm sleep disorder characterized by the inability to sleep on a 24-h schedule. Individuals who are physically or biologically isolated from a normal 24-h light–dark cycle exhibit a sleep–wake cycle that is different from, and usually longer than, 24 h. It is relatively rare in sighted patients and may be associated with delayed sleep phase disorder or psychiatric disorders in some cases. It is much more common in individuals who are totally blind because of the lack of light information reaching the circadian pacemaker in the hypothalamus. We review the clinical characteristics of patients with N24HSWD, discuss the biological mechanisms that may underlie its development, and describe potential treatment strategies.
Original languageEnglish
Title of host publicationEncyclopedia of Sleep
EditorsClete A. Kushida
Number of pages7
ISBN (Print)9780123786104
Publication statusPublished - 2013
Externally publishedYes


  • blindness
  • circadian rhythm sleep disorders
  • free-running type
  • hypernuchthemeral syndrome
  • melatonin
  • non-24-h sleep-wake disorder
  • nonentrained type

Cite this