Narcolepsy is a type of chronic brain disorder that affects your sleep-wake cycles.

The exact cause of narcolepsy is unknown, but experts believe that several factors may play a role.

These factors include autoimmune disease, brain chemical imbalance, genetics, and in some cases brain injury.

Read on to learn more about the possible causes and risk factors for narcolepsy.

A typical night of sleep consists of a pattern of several rapid-eye movement (REM) and non-REM cycles. During a REM cycle, your body goes into a state of paralysis and deep relaxation.

It typically takes up to 90 minutes of non-REM sleep to enter a REM cycle — but when you have narcolepsy, non-REM and REM sleep doesn’t cycle as it should. You may enter a REM cycle in as little as 15 minutes, even during the daytime when you aren’t trying to fall asleep.

Such disruptions make your sleep less restorative than it should be and may wake you up frequently throughout the night. They may also lead to problems during the day, including extreme daytime sleepiness and other narcolepsy symptoms.

Although the exact cause of these disruptions is unknown, researchers have identified several factors that might contribute.

Some evidence suggests that autoimmune disease may play a part in the development of narcolepsy.

In a healthy immune system, immune cells attack invaders such as disease-causing bacteria and viruses. When the immune system mistakenly attacks the body’s own healthy cells and tissues, this is defined as autoimmune disease.

In type 1 narcolepsy, cells in the immune system might attack certain brain cells that produce a hormone known as hypocretin. It plays a role in regulating sleep cycles.

It’s possible that autoimmune disease might also play a role in type 2 narcolepsy. One study published in the journal Neurology found that people with type 2 narcolepsy were more likely than people without narcolepsy to have other types of autoimmune disease.

Hypocretin is a hormone that’s produced by your brain. It’s also known as orexin. It helps promote wakefulness while suppressing REM sleep.

Lower-than-normal levels of hypocretin may cause a symptom called cataplexy in people with type 1 narcolepsy. Cataplexy is the sudden, temporary loss of muscle tone while you’re awake.

Some people with type 2 narcolepsy also have low levels of hypocretin. However, most people with type 2 narcolepsy have normal levels of this hormone.

Among people with type 2 narcolepsy who have low levels of hypocretin, some may eventually develop cataplexy and type 1 narcolepsy.

According to the National Organization for Rare Disorders, research has found that people with narcolepsy have mutations in the T cell receptor gene. Narcolepsy has also been linked to certain genetic variants in a group of genes called the human leukocyte antigen complex.

These genes affect how your immune system functions. More studies are needed to learn how they may contribute to narcolepsy.

Having these genetic traits doesn’t mean that you’ll necessarily develop narcolepsy, but it does put you at higher risk of the disorder.

If you have a family history of narcolepsy, it raises your chances of developing the condition. However, parents with narcolepsy only pass the condition on to their child in about 1 percent of cases.

Secondary narcolepsy is a very rare form of narcolepsy, which is even less common than type 1 or type 2 narcolepsy.

Rather than being caused by an autoimmune disease or genetics, secondary narcolepsy is caused by brain injury.

If you experience a head injury that damages a part of your brain known as the hypothalamus, you may develop symptoms of secondary narcolepsy. Brain tumors may also give rise to this condition.

People with secondary narcolepsy tend to experience other neurological issues as well. These may include depression or other mood disorders, memory loss, and hypotonia (decrease in muscle tone).

A few case reports have suggested exposure to certain infections may trigger the onset of narcolepsy in some people. But there’s no solid scientific evidence that any infection or treatment causes the condition.

Several factors might contribute to the development of narcolepsy, such as autoimmune disease, chemical imbalance, and genetics.

Scientists are continuing to investigate the potential causes and risk factors for narcolepsy, including autoimmune and genetic components.

Learning more about the underlying causes of this condition may help pave the way to more effective treatment strategies.