The exact cause of narcolepsy remains unknown, but various factors — including brain chemicals, genetics, brain injuries, and autoimmune disorders — are likely to play a role.
Narcolepsy is a rare sleep disorder characterized by extreme daytime sleepiness. In some cases, it also involves sudden episodes of severe muscle weakness that occur while awake.
People with narcolepsy can unknowingly fall asleep in the middle of an activity like driving, talking, or speaking over the phone. Muscle weakness (cataplexy), sleep paralysis, and hallucinations are also common symptoms.
Narcolepsy is a sleep-wake disorder. While the precise cause of narcolepsy is not entirely understood, research has shown that a range of factors can play a role in the development of this condition.
Nearly all people with type 1 narcolepsy — or narcolepsy with cataplexy — have low levels of a naturally occurring chemical, hypocretin, that plays a significant role in promoting wakefulness and regulating sleep.
Hypocretins are neurotransmitters — chemicals that send signals between neurons. They are produced by a small cluster of neurons in a brain region called the hypothalamus, which plays a significant role in sleep patterns.
These critical brain chemicals help to prevent rapid-eye-movement (REM) sleep from occurring at the wrong times. Having low levels of hypocretin results in lasting sleepiness and poor control of REM sleep.
For the average person, REM sleep occurs 60 to 90 minutes after falling asleep. People with narcolepsy can enter REM sleep within 15 minutes of falling asleep.
Dreams happen during REM sleep. The brain sends signals to the muscles and limbs during this sleep stage to keep the muscles static to prevent us from acting out our dreams. In narcolepsy, this paralysis mixes into wakefulness, which causes the sudden muscle weakness and vivid hallucinations that people with narcolepsy experience.
With the loss of hypocretins, levels of serotonin and norepinephrine are also lower. As a result, people with narcolepsy may be alert but have extreme difficulties sustaining alertness for long periods.
Ongoing research is also looking at why cataplexy is triggered by certain emotions. The different brain regions that regulate emotional responses are connected with the paralysis pathways.
People with type 2 narcolepsy, previously known as “narcolepsy without cataplexy,” tend to have normal levels of hypocretin.
In recent years, researchers have progressed in understanding what’s behind low hypocretin levels in people with type 1 narcolepsy.
According to the National Institute of Neurological Disorders and Stroke (NINDS), research has suggested that certain genes are strongly related to narcolepsy.
Scientists aren’t sure why hypocretin neurons die in people with narcolepsy, but the answer may lie in immune system abnormalities.
Notably, a gene that plays a role in regulating the immune system — called HLA-DQB1 — is usually responsible for killing off bacteria and viruses, but in people with narcolepsy, it may attack hypocretin-producing neurons. This is why some researchers suggest narcolepsy is an autoimmune disease.
People with a certain variation of this gene — called HLA-DQB1*06:02 — have a higher risk of developing narcolepsy.
Note, though, that only a small percentage of people with this gene variation will develop narcolepsy, so there must be some other genetic and environmental causes at play, too.
In most cases, narcolepsy develops in people without a family history. The NINDS estimates that around 10% of people with narcolepsy with cataplexy will show a family history of the condition.
Though this figure may not be totally accurate, as narcolepsy symptoms can mimic sleep apnea and other sleep disorders.
Trauma to the head can result in sleep disturbances. In some cases, brain injury may have a connection to narcolepsy. Brain injuries affecting the hypothalamus may interfere with the production of hypocretin and result in both sleepiness and cataplexy.
Narcolepsy that develops after a head injury is called secondary narcolepsy, or posttraumatic hypersomnia.
People with brain injuries may experience excessive daytime sleepiness (EDS) and cataplexy for several months after their accident. After six months, those who still experience these symptoms may develop narcolepsy and continue experiencing these symptoms.
However, the chances of a brain injury resulting in permanent narcolepsy are low.
Genetics, environmental factors, and other conditions play a role in narcolepsy.
Narcolepsy is a possible outcome of environmental neurotoxin exposure, common in metalwork and woodwork jobs. Poor ventilation and lack of personal protective equipment can cause an excessive immune response and act as toxins to brain cells.
Some conditions may also increase the risk of sleep disorders, including narcolepsy. These conditions include:
- Multiple sclerosis: a degenerative neurological disease that may cause lesions in hypocretin-producing areas of the brain
- Sarcoidosis: a disease that triggers inflammation in different parts of the body that can damage tissue and interrupt hypocretin production
- Tumors: brain tumors that are impacting the hypothalamus can trigger many sleep disorders
There’s still little research about how lifestyle factors may contribute to narcolepsy. Generally, a lifestyle with a balanced diet, daily exercise, and healthy habits may decrease the risk of brain-related conditions. Yet, these are not strictly associated with the onset of narcolepsy.
If you are concerned that you or a loved one may be experiencing symptoms of narcolepsy, it’s important to seek evaluation by a specialist. They may look at your medical history and suggest a sleep test to rule out narcolepsy. Though there’s currently no cure, treatment for narcolepsy may provide significant relief and help you manage your symptoms.
Living with narcolepsy can often feel isolating and frustrating. Some organizations that provide resources about narcolepsy include:
- Wake Up Narcolepsy
- Hypersomnia Foundation
- Narcolepsy Network
- Project Sleep
- National Sleep Foundation
- The NICER Foundation (Narcoleptics In Crisis Emergency Relief)
Please know, you’re not alone. There may be a narcolepsy support group near you or online that can provide emotional support and fellowship as you learn more about your diagnosis.