Causes
Narcolepsy is a neurological sleep disorder. It is not caused by mental illness or psychological problems. It is most likely the end result of a number of genetic abnormalities that affect specific biologic factors in the brain, coupled with an environmental trigger such as a virus.
Researchers are attempting to come up with a unifying theory involving genetic factors, autoimmunity, and deficiencies in hypocretin, a brain peptide that is important in regulating sleep. Most of the research conducted on narcolepsy uses dogs that have genetic factors that cause narcolepsy, but such studies are helping researchers find the biologic bases to this strange and distressing condition.
Hypocretin and Other Chemicals in the Brain
Hypocretin. Hypocretin (also called orexin) is a peptide that modulates activity in the hypothalamus (the region in the brain associated with sleep, well being, and appetite). Hypocretin specifically has properties that promote wakefulness and inhibits REM sleep. Hypocretin may also have other actions that affect feeding behavior and increase activity in the autonomic (sympathetic) nervous system and systems that regulate motor control. Deficiencies in this peptide have been observed in most patients with narcolepsy who also have cataplexy. Deficiencies might set off the following chemical responses that may produce sleep attacks:
- Lower levels of histamine, a chemical that promotes wakefulness
- Low levels of epinephrine (commonly known as adrenaline), a hormone important in alertness and arousal
- Increase in acetylcholine, which affects REM sleep
- Changes in the enzyme monoamine oxidase, which is believed to be important in preventing arousal
- Changes in dopamine, an important neurotransmitter (chemical messenger in the brain) that helps regulate sleep
- Lower levels of leptin, a hormone associated with obesity when levels decline; (people with narcolepsy tend to be overweight.
- Higher-than-normal secretion of growth-hormone during the day, which may play a role in sudden falling-asleep episodes
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