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

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 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.

One of the causes of narcolepsy is a genetic mutation. In 1999 researchers identified a gene associated with the disorder. The gene in its normal form codes for a protein, hypocretin, that allows cells in the hypothalamus (the part of the brain that 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 have demonstrated an association between narcolepsy and an autoimmune response. In cases of autoimmunity, a person’s immune system attacks the body’s own cells, and in the case of narcolepsy induced by the immune response, this attack is against the specific area of the brain that controls alertness and sleep. Studies have found that cells in these areas are debilitated or destroyed in people with narcolepsy.

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.

Symptoms

Although the symptoms of narcolepsy usually appear during a person’s late teens or early 20s, the disease may not be diagnosed for many years. Most often, the first symptom is an overwhelming feeling of fatigue. After several months or years, cataplexy and other symptoms of the disorder appear.

Cataplexy is the most dramatic symptom of narcolepsy, affecting 75% of people with the disorder. During attacks, the knees buckle and the neck muscles go slack. In extreme cases, the person may become paralyzed and fall to the floor. This loss of muscle tone is temporary, lasting from a few seconds to half an hour, but it is frightening. The attacks can occur at any time but are often triggered by such strong emotions as anger, joy, or surprise.

Other symptoms of narcolepsy include:

There has been debate over the incidence of narcolepsy. It is thought to affect between one in every 1,000-2,000 Americans. The known prevalence in other countries varies, from one in 600 in Japan to one in 500,000 in Israel. The reasons for these demographic differences are not clear. In about 8-12% of cases, people diagnosed with narcolepsy know of other family members with similar symptoms.

The diagnosis of narcolepsy can be made by a general practitioner familiar with the disorder as well as by a psychiatrist. If a person comes to the doctor with reports of both excessive daytime sleepiness and cataplexy, a diagnosis may be made on the patient’s history alone. Laboratory tests, however, can confirm a diagnosis of narcolepsy. These tests may include an overnight poly-somnogram—a test in which sleep is monitored with a variety of electrodes that record information about heart rate, eye movements, brain waves, muscle activity, breathing, changes in blood oxygen concentration, and body position. A Multiple Sleep Latency Test, which measures sleep latency (onset) and how quickly REM sleep occurs, may also be used. People who have narcolepsy usually fall asleep in less than five minutes.

If the diagnosis is still open to question, a genetic blood test can reveal the existence of certain substances in people who have a tendency to develop narcolepsy. Positive test results suggest, but do not prove, that the patient has narcolepsy.

Narcolepsy is a complex disorder, and it is often misdiagnosed. Many people with the disorder struggle with symptoms for an average of 14 years before being correctly diagnosed.

There is no cure for narcolepsy. It is not progressive, and it is not fatal, but it is a chronic disorder. The symptoms can be managed with lifestyle adjustments and/or medication.

People with narcolepsy must plan their days carefully. Scheduling regular naps (either several short, 15-minute naps or one long nap in the afternoon) can help boost alertness and wakefulness. A full eight hours of nighttime sleep should also be a goal. Exercise can often help people with narcolepsy feel more alert and energetic, although they should avoid exercising within a few hours of bedtime. Substances that contain alcohol, nicotine, and caffeine should be avoided because they can interfere with refreshing sleep and with daytime alertness.

Medications for narcolepsy may include the use of antidepressants (tricyclic antidepressants or selective serotonin reuptake inhibitors) to treat such symptoms of the disorder as cataplexy, hypnagogic hallucinations, and/or sleep paralysis.

Stimulants (amphetamines) may also be used to help individuals with narcolepsy stay awake and alert. Modafinil (brand name Provigil) belongs to new class of stimulants known as eugerogics, which have been used to treat narcolepsy in the United States since the late 1990s. Eugerogic stimulants enhance alertness without many of the physical side effects or potential for abuse commonly associated with amphetamines.

With the recent discovery of the gene that causes narcolepsy, researchers are hopeful that other treatments can be designed to relieve the symptoms of the disorder.

Narcolepsy is not a degenerative disease, and patients do not develop other neurologic symptoms. Narcolepsy can, however, interfere with a person’s ability to work, play, drive, socialize, and perform other daily activities. In severe cases, the disorder prevents people from living a normal life, leading to depression and a loss of independence.

Narcolepsy is not a preventable disorder.