Non-24: More Than Just a Sleep Issue

Non-24-Hour Disorder (Non-24), also known as “free-running type,” is a serious chronic circadian rhythm disorder (CRD).1,2 CRDs represent about 10% of the approximately 75 clinical sleep disorders that are formally recognized.3

While abnormal timing of hormonal patterns can confirm the presence of a CRD, patients complain about the consequential circadian rhythm sleep disorder; disturbed sleep being the most commonly reported symptom associated with misaligned circadian rhythms.4

Non-24 occurs primarily in people who are totally blind because they lack the light perception necessary to entrain, or synchronize, the master body clock in the brain with the 24-hour day-night cycle. For these people, the day-night cycle shifts in and out of alignment with the 24-hour social day.1,2,5

In addition to sleep-wake issues, people who are totally blind with Non-24 often experience symptoms in other physiologic systems governed by the circadian system such as cognitive function, mood, and metabolism. These symptoms can occur even in the absence of sleep complaints.1

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References 1. Lockley SW, Cohen D, Harper DG, Uchiyama M. Other circadian rhythm disorders: non-24-hour sleep-wake disorder and irregular sleep-wake disorder. In: Barkoukis T, Matheson JK, Ferber R, Doghramji K, eds. Therapy in Sleep Medicine. Amsterdam, The Netherlands: Elsevier; 2011:411-424. 2. Dressman MA, Licamele L, Feeney J, Polymeropoulos MH. Seventy percent of totally blind people with sleep complaints are not entrained to the 24-hour clock. Poster presented at: 26th Annual Meeting of the Associated Professional Sleep Societies, LLC; June 10, 2012; Boston, MA. Poster 49. 3. Lockley SW. Overview of the CircadianTimekeeping System and Diagnostic Tools for Circadian Rhythm Sleep Disorders. In: Barkoukis T, Matheson JK, Ferber R, Doghramji K, eds. Therapy in Sleep Medicine. Amsterdam, The Netherlands: Elsevier; 2011:363-377. 4. Lockley SW, Arendt J, Skene DJ. Visual impairment and circadian rhythm disorders. Dialogues in Clin Neurosci. 2007;9:301-314 5. Uchiyama M, Lockley SW. Non-24-hour sleep-wake syndrome in sighted and blind patients. Sleep Med Clin. 2009:4;195-211.

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