Narcolepsy Health Article

Definition

Narcolepsy is a disorder marked by excessive daytime sleepiness, uncontrollable sleep attacks, and cataplexy (a sudden loss of muscle tone, usually lasting up to half an hour).

Description

Narcolepsy is the second-leading cause of excessive daytime sleepiness (after obstructive sleep apnea). Persistent sleepiness and sleep attacks are the hallmarks of this condition. The sleepiness has been compared to the feeling of trying to stay awake after not sleeping for two or three days.

People with narcolepsy fall asleep suddenly—anywhere, at any time, even in the middle of a conversation. These sleep attacks can last from a few seconds to more than an hour. Depending on where the sleep attacks occur, they may be mildly inconvenient or even dangerous to the person, particularly if they occur while he or she is driving. Some people continue to function outwardly during the sleep episodes, such as continuing a conversation or putting things away. But when they wake up, they have no memory of the event.

Sleep researchers have identified several different types of sleep in humans. One type of sleep is called rapid eye movement (REM) sleep, because the person's eyes move rapidly back and forth underneath the closed eyelids. REM sleep is associated with dreaming. Normally, when people fall asleep, they experience 90 minutes of non-REM sleep, which is then followed by a phase of REM sleep. People with narcolepsy, however, enter REM sleep immediately. In addition, REM sleep occurs inappropriately in patients with narcolepsy throughout the day.

Causes

One of the causes of narcolepsy is a genetic mutation. In 1999 researchers identified the gene that causes the disorder. The narcolepsy gene allows cells in the hypothalamus (the part of the brainthat regulates sleep behavior) to receive messages from other cells. As a result of the mutation, the cells cannot communicate properly, and abnormal sleeping patterns develop.

Other researchers are also looking into the possibility that narcolepsy may be caused by some kind of autoimmune disorder. This theory suggests that the person's immune system accidentally turns against the specific area of the brain that controls alertness and sleep, injuring or destroying it.

The disorder sometimes runs in families, but most people with narcolepsy have no relatives with the disorder. Researchers believe that the inheritance of narcolepsy is similar to that of heart disease. In heart disease, several genes play a role in being susceptible to the disorder, but it does not usually develop without an environmental trigger of some sort.