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* GSK's Pandemrix shot linked to spike in narcolepsy cases
* Incurable disorder causes sleep attacks and nightmares
* Study finds link in flu protein found in H1N1 flu strainBy Kate Kelland, Health and Science Correspondent
LONDON, July 1 (Reuters) - Scientists investigating why aGlaxoSmithKline flu vaccine triggered narcolepsy in somepeople say they have the first solid evidence the rare sleepdisorder may be a so-called "hit-and-run" autoimmune disease.
The researchers were trying to find out why, of twodifferent flu vaccines widely deployed during the 2009/2010swine flu pandemic, only one -- GSK's Pandemrix -- was linkedwith a spike in cases of narcolepsy.
In a study published in the journal Science TranslationalMedicine, they said the answer could lie in a protein in theH1N1 flu strain found in high amounts in the GSK shot but atmuch lower levels in the other vaccine, Novartis' Focetria.
"It was a really exciting moment," Lawrence Steinman, aprofessor of neurology and neurological sciences who led thework at Stanford University, said of the finding.
A spokeswoman for GSK, whose Pandemrix vaccine was withdrawnfrom the market after the 2009/2010 pandemic, said the companywas aware of the study and would "review it carefully".
"We are actively conducting research into the observedassociation between Pandemrix and narcolepsy and the interactionthis vaccine might have had with other risk factors in thoseaffected," she said in an emailed comment.
Narcolepsy is an incurable, lifelong brain disorder thatdisrupts normal sleep-wake cycles and causes severe nightmaresand daytime sleep attacks that can strike at any time.
Scientists are not sure exactly what causes it, but thelatest research suggests it is a type of auto-immune disease,where the immune system misfires and mistakenly attacks thebody's own functions and organs.
Studies in countries where GSK's Pandemrix vaccine was usedin the 2009/2010 flu pandemic -- including Britain, Finland,Sweden and Ireland -- have found a significant rise in cases ofnarcolepsy in children.
Narcolepsy patients have been shown to have a loss offunction in "wakefulness" cells called hypocretin cells in oneof the brain's sleep centres.
In their study, Steinman's team found that H1N1 pandemic flucontains a protein whose structure partly mimics a portion of ahypocretin receptor in the brain. This H1N1 protein wascontained in both vaccines studied, but at much higher levels inGSK's Pandemrix than in Novartis' Focetria.
The scientists said they now believe the narcolepsy inpeople vaccinated with Pandemrix was caused by a so-called "hitand run" mechanism, in which high levels of the H1N1 proteinstimulated the production of large amounts of antibodies to boththe virus and the hypocretin receptor. (Editing by Larry King)
