There is no evidence that a single gene or genetic variation causes narcolepsy. However, a variety of genes may increase the risk or having conditions that increase the risk of developing narcolepsy.

There are two types of narcolepsy. Narcolepsy type 1 causes cataplexy, excessive daytime sleepiness, unusual sleep patterns, and reduced neurons in the hypothalamus. Narcolepsy type 2 has the same symptoms but without cataplexy — a temporary loss of muscle control.

Researchers have a better understanding of the genetic underpinnings of narcolepsy type 1 than narcolepsy type 2. Even so, many questions remain about the causes of narcolepsy, and most research suggests a combination of genetic and environmental factors.

Unlike some diseases with a strong genetic association, narcolepsy is usually sporadic, which means that people develop narcolepsy even without a family history. However, sometimes narcolepsy clusters in families, suggesting at least some forms of the disease might have a strong genetic association.

Keep reading to learn more about the genetic factors associated with narcolepsy, including the signs and outlook for the condition.

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Researchers have identified a strong genetic link to narcolepsy type 1, which causes narcolepsy and cataplexy.

In narcolepsy type 1, the neurons that contain hypocretin, which doctors may also call orexin, either do not exist or are severely damaged. Researchers think this may be due to an autoimmune disease that causes the body’s immune system to attack these neurons in the brain.

A variation in the specific human leukocyte antigen (HLA) gene, HLA-DQB1*06:02, is present in most people with this form of narcolepsy. This means that this gene likely plays a role, but does not necessarily mean that it is the sole cause, nor that all people with this genetic variant get narcolepsy.

About 20% of people without narcolepsy also carry this variant.

Researchers have less understanding of the causes of narcolepsy type 2, though some studies have found certain genetic variants may increase the risk.

Some rare types of narcolepsy are autosomal dominant, which means that a person will develop the disease if they inherit one gene from a parent for the disease. They include:

  • Autosomal dominant cerebral ataxia, deafness, and narcolepsy, which causes deafness, narcolepsy, and cataplexy. It develops in people who have a mutation in the DNA methyltransferase (DNMT1) gene.
  • Autosomal dominant narcolepsy, type 2 diabetes, and obesity, which causes diabetes and obesity, as well as narcolepsy. This also transfers from parent to child if the child receives a single gene from a parent.

Some other potential causes and risk factors for narcolepsy include:

  • Immune system issues: Unusual activity in the immune system may be a risk factor for narcolepsy. In some people, certain types of influenza may trigger the disease. In Europe, there was an increase in narcolepsy cases in 2009 after widespread H1N1 flu vaccines, but there was no such increase in Canada, which also used the vaccine.
  • Environmental factors: A complex interaction between genes and the environment may contribute to narcolepsy. It may be that certain environmental factors must be present for a person to develop narcolepsy.
  • Brain injuries: Damage to parts of the brain that control sleep and wakefulness, especially to the hypothalamus, may contribute to narcolepsy.

Researchers believe that narcolepsy type 1 is likely an autoimmune disease. Narcolepsy type 2 may or may not be an autoimmune disease. Some evidence suggests there is also a destruction of hypocretin cells in type 2, but that the destruction is less severe.

Five key symptoms may indicate a person has narcolepsy. The acronym CHESS can help people remember:

  • Cataplexy: Cataplexy is a sudden loss of muscle control and coordination. It commonly occurs in people with narcolepsy type 1.
  • Hallucinations: People with narcolepsy may have hallucinations shortly before or as they fall asleep. These experiences may feel like dreams and cause a person to see or hear things that are not actually present.
  • Excessive daytime sleepiness: This is the most common symptom of narcolepsy. People with excessive daytime sleepiness may feel so tired they find it hard to stay awake, even when they get a good night’s sleep.
  • Sleep paralysis: People with sleep paralysis may be unable to move or communicate as they fall asleep or wake up.
  • Sleep disruptions: People with narcolepsy often have unusual sleep patterns and may have difficulty falling back to sleep after waking.

However, most people with narcolepsy do not have all five symptoms. To qualify for a diagnosis, a person needs to have just one of the following:

  • Hypocretin deficiency: Hypocretin helps regulate sleep and ensures people stay awake during the day. Most people with narcolepsy type 1 have very low levels of this brain chemical.
  • Cataplexy: Loss of muscle control and coordination must occur several times a month to qualify for a diagnosis.
  • Abnormal results on multiple sleep latency tests (MSLT): Sleep latency is the time it takes to fall asleep or enter a stage of sleep. People with narcolepsy generally fall into REM sleep within 15 minutes of falling asleep, and fall asleep in 8 minutes or less — and often suddenly. If the average time it takes to fall asleep during five test naps during the day is less than 8 minutes, and two of these naps result in REM sleep, the person will receive a narcolepsy diagnosis.

The symptoms must happen at least three times a week over the last 3 months.

Narcolepsy usually appears between 10–30 years. About half of people develop symptoms when they are teenagers. However, it can develop at any age.

In some cases, a person develops narcolepsy following an injury to the brain, especially to the brain’s hypothalamus.

Doctors diagnose narcolepsy based on symptoms, some of which require medical testing. Having cataplexy, a short sleep latency period, or a hypocretin deficiency is enough to get a narcolepsy diagnosis.

A doctor may also perform additional tests to rule out other causes.

The main tests for narcolepsy include:

  • medical history to check for symptoms of narcolepsy and rule out other causes
  • lumbar puncture to test for hypocretin deficiency
  • sleep study to assess sleep latency period and to assess for other sleep disorders
  • sleep study to assess for other sleep disorders followed by an MSLT

Without treatment, a person may develop new or additional symptoms, though symptoms can also improve with time. Some people with narcolepsy type 2 without cataplexy eventually develop cataplexy, and qualify for a narcolepsy type 1 diagnosis.

Narcolepsy usually responds well to treatment, and people with narcolepsy can lead typical lives. However, there is no cure for narcolepsy.

Without treatment, a person may be unable to work or attend school and experience significant setbacks in their relationships and overall well-being. Depression and other mental health conditions are common among people who have epilepsy.

Narcolepsy has many potential causes. Genetics is only one factor and cannot account for all cases of narcolepsy. People with underlying brain conditions, brain injuries, and some other medical conditions may also develop narcolepsy.

Narcolepsy treatment is the same regardless of the cause. Moreover, knowing that someone is genetically at risk for narcolepsy does not provide information about whether they will develop the condition or how best to treat it.

People who have symptoms of narcolepsy should consult a doctor to explore treatment options.