Scientists in Japan have identified a gene variant that may be linked to narcolepsy -- a condition marked by excessive daytime sleepiness, impaired vision and muscle weakness.

It occurs in 1 out of 2,500 individuals in the United States and Europe, but is at least 4 times more frequent in Japanese.

The researchers analyzed the genomes, or DNA, of 222 narcoleptic Japanese and 389 others who did not have that condition, and one gene variant occurred with significant frequency among those with narcolepsy, they wrote in a paper published in Nature Genetics. (Read more)