Living with narcolepsy can mean experiencing sudden waves of drowsiness, unexpected sleep attacks, or sudden loss of muscle tone during moments of laughter or stress. While treatment options can help manage symptoms, many people still have this question: What causes narcolepsy in the first place?

Researchers know that narcolepsy is a neurological (brain-related) sleep disorder linked to changes in the sleep-wake cycle. However, the full picture is complex. Current studies suggest genetics, the immune system, and environmental factors can all play a role in narcolepsy. This article explores what doctors and researchers know so far about the causes and risk factors.

Types of Narcolepsy

Before discussing the causes, it’s important to know a little about the two main types of narcolepsy. Type 1 narcolepsy includes a symptom called cataplexy. This is when strong emotions, such as laughter, anger, or surprise, cause sudden muscle weakness. People with type 1 may also have very low levels of hypocretin. Also known as orexin, this chemical helps the brain stay awake during the day. Hypocretin also ensures that rapid eye movement (REM) sleep — the period when dreaming happens — takes place at the right time in the sleep cycle.

Type 2 narcolepsy doesn’t cause cataplexy. People with this type have extreme daytime sleepiness and sudden sleep attacks, but their hypocretin levels are usually normal. Most people with narcolepsy — about 80 percent — have this type.

There’s also a rare form called secondary narcolepsy. This happens when a brain injury, illness, or infection damages an area of the brain called the hypothalamus. This is the part of the brain that controls sleep, as well as appetite and body temperature.

Biological Changes in Narcolepsy

The clearest biological change linked to narcolepsy is the loss of brain cells that make hypocretin. In people with type 1 narcolepsy, more than 90 percent of these cells are missing. This sharp drop in hypocretin levels leaves the brain unable to maintain steady wakefulness, which can lead to symptoms of narcolepsy such as:

• Sleep attacks
• Sleep paralysis
• Cataplexy

It’s unclear exactly what causes the loss of these hypocretin-producing cells. However, the immune system may play a role.

Researchers also see signs of what they call sleep-state instability. This means that the brain has trouble keeping sleep and wakefulness separate. As a result, REM sleep can break into daytime hours. People with narcolepsy may dream during short naps or have dreamlike hallucinations as they fall asleep or wake up.

For type 2 narcolepsy, the biological picture is less clear. Most people with this type still have normal hypocretin levels. However, they may have smaller changes in how neurons in the hypothalamus and other brain areas control alertness and REM sleep. Scientists are working to understand just what those changes are.

Genetic Risk Factors

Narcolepsy isn’t passed down in families in a direct way, like eye or hair color. Still, having a family history of narcolepsy can raise your risk. If you have a close family member with narcolepsy, your chances of developing the condition are slightly higher than average. However, the overall familial risk is still low.

Although there’s no single cause of narcolepsy, researchers have identified a strong association between type 1 and a variation in the HLA-DQB1 gene, specifically the HLA-DQB1*06:02 allele (version). The HLA-DQB1 gene plays a role in regulating the immune system, and this particular version is found in about 90 percent to 95 percent of people with type 1 narcolepsy.

People who carry this allele are up to 24 times more likely to develop narcolepsy than people who don’t. However, this version of the gene is also found in about 1 in 4 people in the general population — and most never develop narcolepsy. In fact, only about 25 to 50 in every 100,000 people have narcolepsy. This shows that genetics alone can’t explain the condition.

Studies of identical twins also reveal a mixed picture. If one twin has type 1 narcolepsy, the other has about a 25 percent chance of also having it. That’s much higher than the risk in the general population. However, it also shows that genetics alone don’t determine who gets narcolepsy.

Other genes may also play a role. Many are linked to how the immune system works. This supports the theory that narcolepsy may involve an autoimmune reaction — when the immune system attacks its own healthy cells by mistake. In narcolepsy, the autoimmune reaction may be directed against brain cells that make hypocretin. More research is underway to better understand this theory.

Do You Develop Narcolepsy, or Are You Born With It?

Most people aren’t born with narcolepsy. Instead, the condition tends to develop from more than one risk factor. A combination of genetic risk and an environmental trigger is usually needed for the condition to occur.

Environmental Risk Factors

Although genes seem to play a role in narcolepsy, environmental factors also affect risk. These are outside influences that may trigger the condition in people who are already vulnerable.

One of the strongest clues comes from infections. Studies have found that illnesses such as strep throat or H1N1 influenza (“swine flu”) may raise the risk of narcolepsy. After the 2009 flu pandemic, a higher number of new narcolepsy cases appeared in several northern European countries. Some cases were linked to a flu vaccine called Pandemrix. Researchers believe the vaccine may have triggered the immune system in some children and teens who were already at risk genetically. Importantly, Pandemrix is no longer used, and no other vaccines have shown this connection.

Age also seems to matter. Narcolepsy can appear almost anytime before 50, but most people are diagnosed in their teens or in their 30s. Hormonal changes during puberty may play a role. Children with type 1 narcolepsy may also be more likely to have early puberty or obesity.

What Are the Triggers of Narcolepsy?

Certain situations can make narcolepsy symptoms worse, but they don’t cause the disorder itself. Common triggers include strong emotions like laughter, stress, and anger. Poor sleep habits, irregular schedules, and illness may also increase excessive daytime sleepiness.

Causes and Risk Factors in Secondary Narcolepsy

Compared with type 1 and type 2 narcolepsy, secondary narcolepsy is very rare. This form develops when another condition or injury directly damages the hypothalamus. When this happens, the brain can no longer regulate sleep patterns or maintain steady wakefulness. This can result in the classic symptoms of narcolepsy — excessive daytime sleepiness, sleep attacks, and (sometimes) sleep paralysis.

Unlike type 1, secondary narcolepsy isn’t caused by genetics or immune changes. However, secondary narcolepsy has been linked to several health conditions, including:

• Tumors in the central nervous system (brain and spinal cord)
• Head trauma, such as a traumatic brain injury or concussion
• Stroke
• Multiple sclerosis and neuromyelitis optica spectrum disorder
• Encephalitis (inflammation of the brain)
• Neurocysticercosis (a rare infection caused by a tapeworm)

In each case, damage to brain tissue interrupts how neurons (brain cells) manage REM sleep and alertness. Because secondary narcolepsy is so uncommon, doctors often diagnose it only after ruling out other causes of hypersomnia (sleeping too much) and doing tests such as an MRI.

Can Narcolepsy Be Prevented?

There’s no known way to prevent narcolepsy. Many risk factors — including genetics, immune system changes, and certain brain injuries — are beyond a person’s control. However, practicing good hygiene, such as frequent hand-washing and avoiding contact with people who are sick, may help lower the risk of infections that could potentially trigger narcolepsy. These steps aren’t a guarantee, but they may offer some protection.

Although narcolepsy can’t be prevented, it can be treated. Lifestyle changes, such as keeping a steady sleep schedule and practicing good sleep hygiene, can also improve quality of life.

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