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Researchers from the University of Tokyo have identified a genetic variant linked to a much higher risk of narcolepsy, which may explain the cause of the condition.

Narcolepsy is a rare condition which causes extreme daytime sleepiness, impaired vision and sudden muscle weakness. Sufferers suddenly fall asleep without any warning during a normal activity, and some of them also suffer from "cataplexy", where strong emotions such as anger, surprise, or laughter can trigger loss of muscle strength or lead to collapse.

Scientists believe the cause of narcolepsy may be related to a shortage of a chemical called hypocretin which sends signals to the brain about sleeping and waking up. The condition occurs in 1 in every 2,500 people in the United States and Europe, but is at least four times more common in Japan.

The Japanese researchers analyzed the genomes, or DNA, of 222 narcoleptic Japanese and 389 others who did not have that condition, as well as 424 Koreans, 785 people of European descent and 184 African Americans.

The research found one gene variant occurred with significant frequency among those with narcolepsy and it was linked to an 79% higher chance of narcolepsy in Japanese people, and a 40% increased chance in other ethnic groups - it occurred with significant frequency among narcoleptic Koreans, but the association was not evident in the Europeans and African Americans.

The culprit gene is found close to two genes, CPT1B, and CHKB, which have already been identified as candidates for involvement in the disorder as they both have a role in regulating sleep.

This research could be vital because treatments usually focus on dealing with the symptoms of narcolepsy, but knowing the genetic cause may help to understand underlying cause - in particular what was causing the shortage of hypocretin.

The National Sleep Foundation’s “Sleeptionary” site provides the following information about Narcolepsy. (Sleeptionary content reviewed by Emmanuel Mignot, MD, PhD)

Narcolepsy is a neurological disorder caused by the brain's inability to regulate sleep-wake cycles normally. The main features of narcolepsy are excessive daytime sleepiness and cataplexy. The disease is also associated with sudden sleep attacks, insomnia, dream-like hallucinations, and a condition called sleep paralysis.

Normal sleep happens in cycles. When we fall asleep, we initially enter a light stage of sleep and then progress into increasingly deeper stages. After about 90 minutes, we enter the first stage of REM sleep, which is the dreaming portion of sleep, and throughout the night we alternate between stages of REM and non-REM sleep. For people with narcolepsy, sleep begins almost immediately with REM sleep and fragments of REM occur involuntarily throughout the waking hours. As during REM sleep our muscles are paralyzed and dreaming occurs, it is not surprising that narcolepsy is associated with paralysis and hallucinations.

Narcolepsy is considered a "state boundary" control abnormality. That is, narcolepsy patients sleep a normal amount but cannot control the timing of sleep. 

Narcolepsy affects both sexes equally and develops with age; symptoms usually first develop in adolescence or young adulthood. A combination of genetic and environmental factors may be at the root of this sleep disorder. 

Narcolepsy is often undiagnosed as  sleepiness is not thought to be indicative of disease. Yet the potential dangers of this disorder is reflected in studies showing that narcoleptic patients are more accident-prone and have difficulty with interpersonal relationships.

Researchers believe that narcolepsy may be caused by a deficiency in hypocretin production in the brain. The results of one recent study, in which hypocretin was directly administered to the brain, suggest that using hypocretin derivatives may be an effective way to prevent cataplexy and improve wakefulness.

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