Japan experts identify daytime sleepiness gene

HONG KONG (Reuters) - 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.

"45 percent of those with narcolepsy had this gene variant compared to 30 percent of those without this condition," Professor Katsushi Tokunaga of the department of human genetics at the University of Tokyo said in a phone interview.

Identification of this gene variant could pave the way for experts to hunt for a treatment, Tokunaga said.

The gene is located between the genes CPT1B and CHKB, both of which appear to be linked to the disorder. CPT1B controls an enzyme that regulates sleep, while CHKB is linked to the sleep-wake cycle.

The scientists took a further step to examine that same gene variant in 424 Koreans, 785 people of European descent and 184 African Americans.

It occurred with significant frequency among narcoleptic Koreans, but the association was not evident in the Europeans and African Americans.

"We have no idea why this gene variant occurs with such high frequency among (narcoleptic) Japanese and Koreans ... it may be selection, or chance," Tokunaga said.

(Reporting by Tan Ee Lyn; Editing by Alex Richardson)