Narcolepsy perplexed doctors for decades. They knew that sometimes new cases cropped up after the winter flu season was over. Then, in 2009, doctors around the world began to notice that some people developed narcolepsy after they recovered from the H1N1 swine flu. These trends provided growing signs that narcolepsy was caused by an autoimmune reaction.1-2
The immune system is built to attack foreign invaders such as viruses, bacteria, and fungi. However, sometimes the immune system overreacts to healthy tissue or cells in the body. When this happens it is called an autoimmune disorder (auto means body). Other more common autoimmune disorders include rheumatoid arthritis, multiple sclerosis, and lupus.
Connecting infections, genetics, and narcolepsy
Since 2009, the first solid evidence emerged that narcolepsy is an autoimmune disorder. In general, doctors know that autoimmune conditions are caused by a combination of genetics and environmental factors.
Doctors in 2 different studies found that 2 types of immune cells, CD4+ and CD8 T cells, targeted the brain cells that make hypocretin. T cells play a role in how the immune system works. In people with narcolepsy, 90 to 95 percent of the cells that make hypocretin are destroyed.1-4
The current theory is that T cells attack the brain cells that make hypocretin, a brain chemical that regulates wakefulness. Without enough hypocretin, a person has a hard time staying awake. Doctors believe that changes to the human leukocyte antigen (HLA) complex on chromosome 6 (HLA DQB1*0602) also plays a role in narcolepsy.5-6
HLA DQB1*0602 is found in 12 to 25 percent of the general population and greatly increases the risk of developing narcolepsy. Other genes and environmental factors increase or decrease that risk. Only 1 percent of people with HLA DQB1*0602 go on to develop narcolepsy.4
Together, this means that people with these genetic changes have a greater risk of developing Type 1 narcolepsy if certain things happen, such as if they catch the flu or strep throat.5
Other autoimmune disorders and narcolepsy
In 2016, a small study from Spain found that people with Type 1 narcolepsy had a greater risk of having a second autoimmune condition. The other autoimmune diseases found in these people were:7
- Multiple sclerosis
- Lupus
- Psoriasis
- Crohn’s disease
- Ulcerative colitis
- Celiac disease
- Allergies
- Asthma
- Atopic dermatitis
This study also found that people with Type 1 narcolepsy had more severe cataplexy if they had multiple autoimmune disorders.7
These findings only apply to Type 1 narcolepsy with cataplexy. Doctors do not know what causes Type 2 narcolepsy. Some theories suggest that it is caused by a less severe injury to the area of the brain that makes hypocretin.4