Narcolepsy

New evidence supports the view that the sleep disorder narcolepsy is an autoimmune disease. Individuals with narcolepsy suffer from difficulty staying awake during the daytime especially when stressed. It can be an extremely debilitating problem.

One possible explanation that has been proposed for narcolepsy is that it is caused by low levels of hypocretin, a neurotransmitter that is involved in the regulation of sleep and wakefulness. One possibility is that the low levels are due to a malfunction of the immune system (i.e. an autoimmune disorder). The immune system normally attacks invading cells such as bacteria and viruses but in the case of autoimmune disorder the system malfunctions and attacks healthy cells. The cells that are attacked are neurons that produce hypocretin, resulting low levels of hypocretin (also called orexin).

Elizabeth Mellins and Emmanuel Mignot (De la Herrán-Arita et al. 2013) have produced the first direct evidence of such immune system activity: a special group of CD4+ T cells (a type of immune cell) that targets hypocretin.

What remains unclear is why some people produce these T cells. It may be due to genetics but may equally be due to environmental factors (e.g. infections), or both. Mellins has proposed that narcolepsy develops when people with a genetic predisposition encounter an environmental factor that mimics hypocretin, triggering a response from the immune system and the onset of the autoimmune disorder. This happened recently during the 2009 swine flu epidemic when there was a sudden increase in cases of narcolepsy – what would happen is that genetically vulnerable people would react to exposure to the virus by producing an the special T cells and these would affect hypocretin producing cells.

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