Types and Causes of Narcolepsy
Narcolepsy is a fairly rare sleep disorder. A person with narcolepsy falls asleep unwillingly for a few seconds to several minutes, often several times a day. These “sleep attacks” can occur in the middle of an activity, such as driving, eating, working, or talking. Some people with narcolepsy go limp or lose muscle tone. This is called cataplexy.1
Types of narcolepsy
Narcolepsy is a sleep disorder in the category hypersomnia of central origin. “Hyper” means too much and “somnia” means sleep. Narcolepsy is the most studied and best understood of the hypersomnias.
The 2 most common types of narcolepsy are:1
Type 1 narcolepsy, which is sometimes called narcolepsy with cataplexy. Cataplexy is a loss of muscle tone that may cause falls or a droopy face. Most people with type 1 narcolepsy have low levels of the brain hormone hypocretin. Hypocretin is also called orexin. Cataplexy is often triggered by strong emotions such as surprise, fear, or laughter.
Type 2 narcolepsy, which is sometimes called narcolepsy without cataplexy. People with Type 2 narcolepsy experience daytime sleepiness but not the muscle weakness triggered by emotions. Most people with Type 2 narcolepsy have normal levels of hypocretin.
A rare type of narcolepsy, secondary narcolepsy, can occur if the hypothalamus is damaged during a head injury. The hypothalamus is an area deep in the brain that helps control sleep. People with this form of narcolepsy may sleep for 10 or more hours each night and may have other neurological problems such as multiple sclerosis or a brain tumor.1,4
Narcolepsy is sometimes confused with idiopathic hypersomnia (IH). People with idiopathic hypersomnia sleep for long periods but do not feel refreshed like those with narcolepsy. They do not have cataplexy or “sleep attacks.” IH is rare.4
What causes narcolepsy?
Doctors believe that most cases of Type 1 narcolepsy are caused by a combination of genetics and the environment. It is now considered to be an autoimmune disease. That’s because doctors in Europe noticed that people sometimes developed narcolepsy after recovering from an infection like some strains of the flu virus. People tend to develop narcolepsy in their mid-teens or mid-30s.1,3,4
An infection may trigger the immune system to begin attacking the brain cells that make hypocretin. The loss of hypocretin then causes Type 1 narcolepsy.1,3
People with narcolepsy often have changes in a T cell receptor gene. T cells play a role in how the immune system works. This means that people with this genetic change have a greater chance of developing Type 1 narcolepsy if certain things happen, such as catching certain flu viruses. The human leukocyte antigen (HLA) complex on chromosome 6 may also play a role in whether someone develops narcolepsy.4
It is rare for someone with narcolepsy to have a family history of the condition. Only 10 percent of those who have narcolepsy with cataplexy have a close relative with the condition.1
It is rare, but sometimes a head injury can cause narcolepsy if the brain cells that make hypocretin get damaged.1
Doctors do not know exactly what causes Type 2 narcolepsy, or narcolepsy without cataplexy.4
Narcolepsy is a fairly rare condition. However, some doctors believe it may be undercounted since narcolepsy is often incorrectly diagnosed as a mental health or seizure disorder.1