What Causes Narcolepsy

The cause of narcolepsy is not yet fully understood; however significant progress has been made identifying the differences between someone with narcolepsy and someone without.

It is widely accepted that narcolepsy is a neurological disorder, caused by reduction or eradication of the brain chemical (neuropeptide) Hypocretin – also known as Orexin. These chemicals are usually made in the Hypothalamus region of the brain. They are known to regulate sleep and wakefulness, appetite and other behaviours. People with narcolepsy have been found to have either dramatically reduced or complete absence of Hypocretins.

It is understood that the neurons in the Hypothalamus section of the brain, that create Hypocretins have died. These neurons cannot regenerate naturally and currently, there is currently no way to replace either the neurons or the Hypocretin.

What triggers Narcolepsy:
The triggers for narcolepsy are also not fully understood but are believed to be a combination of one or more of the following:

Genetic Disposition
Most people who develop narcolepsy share a genetic trait. This variation of the gene HLA-DQB1 is found in up to 25% of the population. Having this variation does not mean that you will develop narcolepsy, but that there is slightly elevated risk .

Only a small proportion of cases of narcolepsy recorded are thought to be genetically inherited, though cases of multiple family members with narcolepsy do exist. Immediate relatives of someone diagnosed with narcolepsy are only marginally more likely to develop the condition themselves. 

Auto-immune response
The particular gene (in HLA complex) which has been identified in most people with narcolepsy, is part of a group of genes which are thought to play a role in auto-immune response: distinguishing between internal bodies and foreign invaders (viruses or bacteria).

It is understood that the auto-immune system triggered by some external trigger (see below) but misidentifies the Hypocretin-generating neurons as part of that response and kills them.

External Triggers
There is thought to be an external trigger which activates the auto-immune system which goes on to attack the Hypocretin-generating neurons. An elevated level of antibodies which fight strep and other infections have been recorded in people with newly developed narcolepsy. Narcolepsy is found to develop most commonly in late spring. This seasonal pattern and the trend in the antibodies has led to the theory that the immune system may be triggered by a winter infection.

Another identified trigger is the Swine Flu vaccine Pandemrix which was administered in response to the global Swine Flu outbreak. This vaccine was administered in Ireland and other countries from 2009.   A significant spike in the number of new cases of children developing narcolepsy was recorded in the weeks and months after receiving the vaccination. By 2010 investigations were launched in European countries into a link between the vaccination and narcolepsy in children because of this spike. This investigation demonstration an increased risk of narcolepsy – minimum 6.6 fold – as a result of receiving the Pandemrix vaccination. There is no known link between other Swine Flu vaccinations and narcolepsy.

Narcolepsy tends to develop in early adolescence, though it can develop at any age. Narcolepsy resulting from the Pandemrix vaccination does not follow this age profile. There was a significant spike in the number of younger children developing narcolepsy because of the Pandemrix vaccination.