My sister has had trouble with being sleepy all the time and was recently told she has narcolepsy.

She was warned that sometimes she may suddenly collapse and fall asleep. She was also told that it is genetic.

I?m now afraid that this will happen to me, and I feel very anxious when I?m driving. Please help me understand narcolepsy better. ? J.H., Chicago Ridge, Illinois.

About 1 in 2,000 people in the United States are diagnosed with narcolepsy.

Recent research has found a specific area of the genes where changes increase the risk of developing this condition. But the chances of a relative getting the disease are still quite low. For example, even if you were 4 times more likely to develop narcolepsy, your risk would only be 1 in 500.

I suggest that you approach your situation by understanding what narcolepsy is, making sure that your sister?s condition is in fact narcolepsy, and, of course, helping her deal with her condition.

Narcolepsy is an uncommon sleep disorder, in which cataplexy (sudden collapsing due to muscle weakness) may or may not occur. Narcolepsy does not usually have serious medical consequences, but it can be frightening and may increase risk of accidents.

The cause is unknown. But very recent evidence indicates that it may result from a deficiency in special types of chemical transmitters in the brain called orexins and hypocretins. This in turn has been shown to be related to a gene that is part of the development of the immune system.

The disorder typically begins in adolescence and early adult life and affects both sexes equally. Symptoms usually level off in severity at around 30 years of age, but the disorder persists throughout life. Onset after age 40 is very unusual.

The first symptom of narcolepsy is almost always generalised daytime sleepiness. After this early stage, narcolepsy is characterised by sudden, recurrent, brief, unintended and uncontrollable sleep attacks in inappropriate situations. Other symptoms of narcolepsy can include visual or auditory hallucinations.

The sleep attacks may occur during any type of activity, but they are usually more common during low-stimulation, low-activity, monotonous situations, such as boring meetings, long periods of highway driving, or talking on the telephone.

These sleep episodes generally last 10 to 20 minutes but can last up to an hour if not interrupted. Dreaming is frequently reported.

Narcolepsy is also associated with a condition known as cataplexy, defined as a loss of muscle tone resulting in a momentary paralysis without losing consciousness. It?s usually in response to a sudden intense emotional reaction. Episodes usually last a few seconds or minutes.

Cataplexy often develops several years after onset of daytime sleepiness. The severity of loss of muscle tone can range from almost imperceptible (drooping eyelids) to buckling at the knees and actually falling to the ground.

Diagnosis of narcolepsy, especially if someone does not have cataplexy or sleep attacks, should be based sleep studies.

Stimulant drugs such as ephedrine, amphetamine, dextroamphetamine and methylphenidate (brand name Ritalin) may help reduce episodes of narcolepsy. Sodium oxybate, also known as gamma-hydroxybutyric acid (GHB), has been shown to be effective. Unfortunately, all of these drugs have a higher potential for abuse.

A new drug, modafinil, is a wake-promoting agent with a different mode of action from the amphetamines and amphetamine-like drugs. Modafinil has been shown to be effective and well tolerated. It also offers a lower potential for abuse and dependence. Imipramine, an antidepressant, usually helps relieve the cataplexy.

Attention deficit-hyperactivity disorder was found to be associated with iron deficiency.

Recent research showed that levels of iron in those with ADHD average about half of those without ADHD. It also found that 4 out of 5 children with ADHD had below-normal levels.

The researchers suggest that everyone with ADHD be tested for iron, and at least that all of those with low levels be given iron supplements and retested until their iron levels become normal.

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