Causes of Narcolepsy

Genetic Factors

Narcolepsy has a genetic component and tends to run in families. Experts estimate that around 8 – 10% of people with narcolepsy have a close relative who has the disorder. A 2006 study reported that the risk for narcolepsy among male first-degree relatives (parents or sibling) was 105 times higher than the general population; the risk for female first-degree relatives was 54 times higher. Other studies suggest that people who have a first-degree relative with narcolepsy are 20 – 40 times more likely to have narcolepsy than other people.

However, most experts agree that genetics are not the only factor involved in narcolepsy. Narcolepsy most likely involves a combination of genetics and one or more environmental triggers such as infection, trauma, hormonal changes, immune system problems or stress. Researchers are looking for specific genetic mutations that may make individuals susceptible to this disorder.

Autoimmunity

It has been theorized that narcolepsy may be an autoimmune disease, in which the immune system may be tricked into perceiving its own proteins to be antigens. (Antigens are foreign substances targeted for attack by immune factors in the body.)

Important autoimmune diseases include multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and type 1 diabetes. In such diseases, the immune system overproduces potent factors called cytokines, which cause inflammation and injury in the susceptible cells and tissues affected by the disease. Most autoimmune diseases also tend to afflict those with particular genetically determined molecules of the immune system called human leukocyte antigens (HLAs).

Experts suggest that an immune attack in narcolepsy may occur against cells containing the brain peptide hypocretin (orexin), resulting in deficiencies that are now believed to be major components of the narcolepsy process. HLAs, particularly a subgroup known as (HLA)DQB1-0602, have been strongly associated with narcolepsy and low levels of hypocretin. Narcolepsy patients who carry this HLA group tend to have a specific syndrome of symptoms that include cataplexy and periodic limb movement disorder. However, between 20% and 40% of people without narcolepsy carry these HLA types.