Scientists in Japan have identified a genetic mutation linked to narcolepsy, a disease that can cause someone to doze off in
mid-sentence or behind the wheel of a car, a study reports.
Other symptoms of the condition, which shows up in late adolescence
or early adulthood, include excessive daytime drowsiness, vivid
hallucinations on the threshold of sleep, and the sudden, temporary
loss of muscle control, often triggered by emotional shock.
A team of researchers led by Katsushi Tokunaga at the University of
Tokyo compared the genetic profiles of persons with and without the
Across four different ethnic groups, patients with narcolepsy were
far more likely to carry a specific mutation of DNA located between two
genes, one of which has been associated with sleep regulation and the
other with the sleep-wake cycle.
Genetic variant common in Koreans
The statistical link was strongest among Japanese, but remained
significant among Europeans and persons of African descent as well.
The study also showed that the suspect genetic variant - known as
rs57770917 - is common among Koreans.
The prevalence of the disease varies widely in different countries.
In Europe and the United States, narcolepsy is roughly as common as
Parkinson's disease or multiple sclerosis, affecting on average one in
every 2 500 people.
But in Japan the frequency is four times higher, while in Israel
only one in half-a-million people have the condition. There is no known cure for narcolepsy, which is often treated with stimulants to combat daytime fatigue.
Previous studies had already pointed to genetic factors as playing a
role. An immediate family member with narcolepsy increases one's chances
of having the disease by 10 to 40 times.
It was found that all Japanese suffering from the disease carried
another genetic variant. But fully ten percent of the Japanese
population shared that same mutation, so researchers suspected the
existence of additional genetic drivers as well.
The authors of the new study said their findings could point the way
to "new therapeutic approaches" designed to target the neurochemical
reactions patterned by the wayward genetic material.
The research was published in journal Nature Genetics, part of the
British-based Nature Publishing Group. – (Sapa, October 2008)