A common gene variant could play a causal role in narcolepsy, a disorder where a person is extremely sleepy and has "attacks" of sleep for periods of time, even in the daytime, according to a new study.
People with the gene variant -- called DQB1*06:02, and discovered on an allele in the human leukocyte antigen system (involved in functioning of the immune system) -- were 251 times more likely to experience narcolepsy with cataplexy. Cataplexy is a symptom of narcolepsy that involves sudden body muscle weakness brought on by emotion.
Researchers also found that nearly all people with narcolepsy with cataplexy have this gene variant (a 99.32 percent "negative prediction value").
The extremely strong association between narcolepsy and this particular gene variant "suggests a causal implication," study researcher Mehdi Tafti, a professor in the Center for Integrative Genomics at the University of Lausanne and Lausanne Hospital, said in a statement.
However, the researchers also noted that this particular gene variant is quite common -- it exists in about one in five people in Europe -- and has a predictive value of 65.68 percent. But the findings do suggest that doctors "should reconsider the diagnosis of narcolepsy with cataplexy in HLA DQB1*06:02 negative patients," Dr. Nathaniel Watson, a spokesperson for the American Academy of Sleep Medicine, said in a statement.
The findings, published in the journal Sleep, are based on genetic analysis of 1,261 people with narcolepsy and 1,422 controls.