Swiss scientists say the trigger they have found for narcolepsy, the health disorder that sparks sudden daytime bouts of tiredness or sleep, could open up new avenues for treatment.
The protein, called Trib2, is produced by neurones that also secrete the substance which helps keeps people awake, hypocretin, the researchers at Geneva and Lausanne Universities said in a statement.
Narcolepsy, which affects some 0.05 percent of the population on average, has already been associated with a hypocretin deficiency but the exact cause had never been pinpointed.
The researcher team concluded that narcolepsy was the result of an attack by the body's own immune system, after they found high levels of Trib2 antibodies amongst a sample of 120 narcoleptic patients.
The antibodies end up destroying the hypocretic neurones.
Professor Mehdi Tafti, co-director of the sleep laboratory at Vaud University Hospital in Lausanne, said that treatment with immunoglobulin, which is commonly used for auto-immune diseases of the nervous system, had shown "extraordinary results."
The sleep disorder disappeared in most of the patients treated soon after first symptoms, the statement added.
The Swiss researchers hope the discovery could also shed more light on the way the human body handles sleep.
The results were published in the Journal of Clinical Investigation.