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Causes
By Mayo Clinic staffThe exact cause of narcolepsy isn't known. It's believed that genetics may play a role. But the larger influence may be a trigger, such as an infection, that leads to damage to certain brain cells important to sleep.
Normal sleep pattern vs. narcolepsy
The normal process of falling asleep begins with a phase called non-rapid eye movement (NREM) sleep. During this phase, your brain waves slow down considerably. After an hour or two of NREM sleep, your brain activity picks up again, and REM sleep begins. Most dreaming occurs during REM sleep.
In narcolepsy, however, you suddenly fall into REM sleep without first experiencing NREM sleep and at abnormal times, such as during the day. Also, some of the aspects of sleep that normally occur only during REM sleep, such as sudden lack of muscle tone, sleep paralysis and vivid dreams, occur at other times during sleep in people with narcolepsy.
The role of brain chemicals
Hypocretin is an important chemical in your brain that helps regulate staying awake and keeps REM sleep stable and occurring at the appropriate time during sleep. The cells that make hypocretin are severely damaged in narcolepsy. Because the cells are damaged, hypocretin is found in low levels in people with narcolepsy — lowest of all in those who experience cataplexy.
Exactly what causes the damage to hypocretin cells is not known. But it's thought that there's probably some factor such as an infection and an abnormal immune response that leads to the damage. Certain genetic markers are also more common in people who develop narcolepsy. If another family member has narcolepsy, it is slightly more likely you could develop it.
Research continues to focus on whether an abnormal gene may be responsible for narcolepsy or if the body's immune system may be involved in mistakenly attacking hypocretin-producing cells in the brain.
The low levels of hypocretin may even lead to the development of a diagnostic test for narcolepsy. Hypocretin is normally present in spinal fluid of people without the disorder, but is present in only very low levels in the spinal fluid of people with narcolepsy.
