Types and Causes of Narcolepsy: An Explainer

Health Professional, Medical Reviewer

Most people think of narcolepsy as a condition in which people cannot contain themselves from falling asleep. That is not entirely accurate. Narcolepsy is a condition in which it’s difficult for the person to stay awake. Semantics you say?  Not exactly.

What is the cause of Narcolepsy?

Narcolepsy is known by the triad of symptoms:

Narcolepsy involves a deficiency or absence of a hormone called orexin (also called hypocretin), which is produced in the brain.  This is one of the hormones that works to keep us awake.

Why two names for the same hormone - orexin and hypocretin?

As can sometimes happen, two separate research groups were working at the same time on the same compound. Researchers at the University of Texas were investigating a hormone in mice that regulated appetite, and named it orexin.  Researchers at Stanford University were investigating a hormone in dogs, involved in regulation of sleep and called it hypocretin. The hormone ended up being discovered simultaneously at two different centers.

Researchers found that orexin and hypocretin turned out to be the same hormone, but neither side would relent on the name.  So this hormone goes by two names, which can sometimes be a bit confusing to the average layperson.

What causes a deficiency in this hormone?

There are many theories.  One theory, the genetic theory, identifies a gene called HLA DQB1602 - believed to be responsible for the hormone, and can ultimately contribute to the production or lackthereof of the hormone. There is also an infectious theory based on a large number of cases of narcolepsy that appeared to occur followed an infection with a strain of streptococcus.  The strep infection resulted in antibodies that attacked the brain structure and caused lower levels of the hormone.  Others suggest that narcolepsy could be a consequence of post head trauma.   Most experts believe that in most cases, narcolepsy is idiopathic and there’s no clear cause.

Are there different classes or types of narcolepsy?

There are two classes of narcolepsy, based on the presence (or absence) of a phenomenon called cataplexy. Narcolepsy with cataplexy (narcolepsy type I) and narcolepsy without cataplexy (narcolepsy type II) obviously have significant differences.

What is cataplexy?

Cataplexy is a condition in which people who have a sudden emotional stimulus, such as laughter or anger, suddenly experience muscular paralysis and fall on the floor.** Or the phenomenon can be more subtle, sometimes in children or teenagers, and you witness a facial grimace in response to the emotional stimulus.

How does cataplexy relate to the problem of staying awake or being sleepy?

The answer is directly linked to the hormone and the larger role that orexin plays.  Orexin does more than just keep us awake.  This hormone also regulates the different stages of sleep.  As I previously discussed, there are three parts to the non-REM phase of sleep called N1, N2, and N3.  There is also another stage of sleep called REM.  There is a drastic difference between REM and the non-REM stages, so there must be a smooth transition between them during sleep.  Orexin apparently plays a crucial role in that smooth transition.

The absence of orexin will create jolting consequences, including the appearance of REM “sleep” at inappropriate times, i.e. wakeful hours.

To make sense of cataplexy and orexin deficiency, it's best to first unravel what happens during the REM phase of sleep.  REM is what happens when we dream. During this deep, dreaming phase, the brain send signals to the spinal cord, suppressing all muscle activity.   So we are, in a way, paralyzed, with movement completely prevented so we don’t physically act on our dreams.

When there is the lack of orexin there is a lack of organization of the different sleep stages, so REM can actually happen when we are awake.

So cataplexy is the appearance of the muscle paralysis that occurs during REM except that it occurs during wakeful hours.  That explains why individuals can suddenly fall to the floor.

What are some other symptoms of narcolepsy that are explained by cataplexy?

Imagine being in bed, awake and being paralyzed and unable to move.

Imagine having an actual dream, but being awake or waking up in the middle of a dream (not once it’s over).

These are other signs of narcolepsy called sleep paralysis and hypnagogic hallucinations.  Both presentations can be quite dramatic.  There have even been cases where people experiencing this phenomenon have called the police, believing that there was an intruder in their room.

See more helpful articles:

How to Diagnose and Treat Narcolepsy

Missed Diagnosis: A Race Car Driver's Journey With Narcolepsy

Eating Disorders Linked to Narcolepsy