The narcolepsy disorder that is characterized by excessive daytime sleepiness did not come to be known until 1870. It was well over 100 years, just about fifteen years ago around the turn of the 21st century, before any underlying causes for the condition became clear. This came about as a result of groundbreaking discoveries and new insights from two doctors; Dr. Jerome Siegel from the University of California at Los Angeles and Dr. Emmanuel Mignot at Stanford University.
The primary cause of narcolepsy is a lack of hypocretins which are neurotransmitters that transmit signals from one neuron to another neuron. Hypocretin are produced by a small cluster of neurons in an area of the brown known as the hypothalamus. This section is located directly behind the eyes.
There are only about 100,000 to 200,000 hypocretins that are produced during the human state of wakefulness which bind to certain protein receptors, increase the activity of the neurons and work to prevent REM (rapid eye movement) sleep from occurring at the wrong time of day (as well as promote alertness throughout the day). Scientists can determine the amount of hypocretins in the brain by measuring the amount of cerebrospinal fluid which surrounds the brain. The results in those individuals who were diagnosed as having a narcolepsy with cataplexy are shown to have up to a 95% decrease in their hypocretin producing neurons.
The hypocretins that are produced in the morning die off which explains how people with narcolepsy start off in a state of alertness but gradually feel more and more tired as the day goes on; unlike those with other sleep disorders such as obstructive sleep apnea where people do not usually receive a good night’s sleep and feel tired from the moment they wake up. This also leads to a REM sleep that is poorly regulated and a lasting sleepiness to the point that the nonstop sleeper has to take a twenty minute power nap throughout the day just to main a few extra hours of wakefulness; particularly if they are getting behind the wheel of a car.
The lack of hypocretins that causes the poorly regulated REM sleep also causes the temporary paralysis and dreaming that occur only during REM sleep to mix into the wakefulness state during the day. The result being an individual who suffers from narcolepsy can have a hard time distinguishing between their awake states and their sleeping states; depending on the severity of the condition of course. At its worst the condition of narcolepsy can lead to dream-like hallucinations and cataplexy which is a partial paralysis that occurs upon falling asleep and upon waking up. Though cataplexy only lasts a couple minutes it can be scary, especially if it happens in the morning since the paralysis can make the person wonder if they are having a stroke which typically occurs in the morning.
While many patient who are diagnosed with narcolepsy do not have associated cataplexy, many may only have one or two episodes of cataplexy throughout their life. Those with a more extreme form of the condition can have up to twenty episodes a day which could be embarrassing if in public, or even fatal if they are driving a motor vehicle.
Only a sleep study can reveal whether a person has narcolepsy, with or without cataplexy, or some other sleep disorder such as sleep apnea. It also can be noted that there is a fine line between narcolepsy and mental illness, such as depression. This is because the neurons that are essential for maintaining wakefulness and alertness are the neurotransmitters known as norephinedrine (which provides the adrenaline that the body runs on) and serotonin. A shortage of the latter can cause a person to feel low energy, depressed, or even anxious. The hormone melatonin is what gets released at night when it is dark to promote sleep and overflows into serotonin so when sleep is poorly regulated this can lead to an imbalance. This would be the leading rationale as to why antidepressants are often used to treat patients with narcolepsy.
These two neurotransmitters also serve to block paralysis in the lower brain stem and the lower spinal cord so paralysis usually happens because of the imbalance in serotonin and norephinedrine due to the loss of hypocretins. The paralysis can be triggered by negative emotions such as anger and crying. In a study performed with dogs and cats, tasty food also triggered cataplexy which proves that even positive emotions can trigger the paralysis as well. The positive emotions typically occur during a state of arousal when the dopamine, another neurotransmitter, is elevated. An example would be laughing at a funny joke so hard that it sets off an episode of cataplexy.
Lastly, narcolepsy, like many other conditions, is genetic. Ongoing research has found a gene code that contributes to narcolepsy, this gene is human leukocyte antigen DQB1 06:02 which is an important to maintain healthy immune function. That finding would make narcolepsy an autoimmune disorder that can be triggered by as little as a seasonal infection such as streptococcus, or strep throat. The gene is estimated to only be in anywhere from 12% to 25% of the population even though only as little as one or two percent of population may experience the illness.