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National Center for Biotechnology Information (US). Genes and Disease [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 1998-.

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Genes and Disease [Internet].

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Narcolepsy

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Narcolepsy is a sleep disorder. Affected individuals are extremely drowsy during the daytime and may fall into a deep sleep at any time. After a short nap, the patient may feel refreshed, but it is only a short period of time before drowsiness returns.

The second major symptom of narcolepsy is called cataplexy. Cataplexy refers to a sudden weakness of the muscles that leads to collapse. This is often triggered by an emotional response such as laughter, surprise, or anger.

The normal stages of sleep include a phase of rapid eye movement (REM). It is during the REM phase of sleep when we dream and during this time that our muscles become completely relaxed. The problem in narcolepsy is that REM can occur while awake, resulting in half-sleep dreams and temporary paralysis.

The genetics of narcolepsy is complex, but it is thought that a newly discovered group of proteins may be involved. These proteins are called hypocretins (also known as orexins), and they signal messages in the brain. When hypocretins are given to rats, they induce wakefulness. Dogs that have a mutation in the hypocretin receptor Hcrt2 have narcolepsy. Mice that have a mutation in the hypocretin gene also have narcolepsy. A mutation in the hypocretin gene is extremely rare in human narcolepsy. However, affected individuals do have very low levels of hypocretins, suggesting the loss of the brain cells that secrete hypocretin.

Although there are rare families where narcolepsy is passed on through several generations, most cases of narcolepsy occur at random rather than being inherited. The likelihood of developing narcolepsy is influenced by proteins known as histocompatibility leukocyte antigens (HLA). HLA refers to a group of proteins (antigens) that influence the level to which white blood cells (leukocytes) accept transplanted tissue (histocompatibility). It is now known that hypocretin deficiency in humans is closely associated with the HLA protein DQB1*0602. It has been suggested that the cause of human narcolepsy is the body's immune cells attacking and damaging the neurons that secrete hypocretin.

The daytime sleepiness of narcolepsy is treated with stimulants similar to amphetamine, and cataplexy is treated with antidepressants. More effective treatments are being investigated and may include replacing the missing hypocretins with drugs that stimulate the hypocretin receptors.

As our understanding grows about the mechanisms that underlie sleeping, wakefulness, and narcolepsy, we will progress toward finding a cure for this disease.

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Websites

  • MEDLINEplusMedical encylopedia from the National Library of Medicine, NIH
  • FactsheetPatient information from National Institute of Neurological Disorders and Stroke, NIH

Related information

  • OMIM
    Related OMIM records

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