A genome-wide screen performed by Japanese scientists has uncovered a genetic variant linked to an increased risk for narcolepsy - a sleeping disorder marked by excessive daytime sleepiness, loss of muscle function and hallucinations.
Researchers at the University of Tokyo compared the genome of 222 narcoleptic Japanese and 389 individuals without the disorder and found a genetic variant - a single letter change in their genetic code - that increased carrier's chances of having the disorder by 79 per cent.
Professor Katsushi Tokunaga, who led the study, which was published in the journal Nature Genetics, explained that '45 percent of those with narcolepsy had this gene variant compared to 30 percent of those without this condition'.
Genetic causes of narcolepsy, which is four times more common in Japanese compared to Europeans, have been hard to pin down. Autoimmunity has been mooted as a possible source - this is where the body's immune system malfunctions and, instead of attacking viral or bacterial invaders, turns on itself, in this case on proteins involved in regulating human circadian (sleep) rhythms, dampening their effect.
Narcoleptics are known to have a reduced level of hypocretin - a protein with a known function in metabolic pathways important in sleeping and eating - but the reason for this reduction and how important a role it plays is not known.
The variant found in the most recent study is located between two genes: CPT1B and CHKB - both of which are involved in the modulation of REM sleep - a light, dream-filled phase of sleep important in the developing brain and memory consolidation. The mechanism by which the variant influences either one or both of the genes is, as yet, unclear.
Having found the variant, the researchers went on to look at its distribution in Korean, European and African American populations. The variation was found in a significant proportion of narcoleptic Koreans, but was not present in European or African American groups.
The researchers hope the findings will contribute to scientists' understanding of the genetic processes that lead to narcolepsy, perhaps helping to lead to the development of new therapies for the disorder.