That finding was based on 39 people with type 1 narcolepsy, and 35 people without the disorder -- including four sets of twins in which one twin was affected and the other was not.
It's known that genetic susceptibility plays a role in narcolepsy. And the theory, Mellins explained, is that in people with that inherent risk, certain environmental triggers may cause an autoimmune reaction against the body's own hypocretin.
Infections are the main culprit, and there is already evidence that the H1N1 "swine" flu is one trigger. In China, Mellins noted, there was an upswing in childhood narcolepsy cases after the H1N1 flu pandemic of 2009.
And in 2010, a cluster of narcolepsy cases in Europe was linked to a particular H1N1 vaccine that contained an "adjuvant" designed to induce a stronger immune system response. That vaccine, called Pandemrix, is no longer in use.
All of that led experts to speculate that in some genetically vulnerable people, the H1N1 virus could cause T cells to mistakenly attack hypocretin-producing brain cells.
And in the current study, Mellins's team found that segments of the H1N1 virus were similar to portions of the hypocretin protein -- the same portions that activated narcolepsy patients' T cells. They say that supports the idea that certain infections confuse T cells into attacking hypocretin-producing cells.
An expert on sleep welcomed the new study.
"They're providing more-compelling evidence that this is an autoimmune disease," said Dr. Nathaniel Watson, an associate professor of neurology at the University of Washington in Seattle, and a member of the board of directors for the American Academy of Sleep Medicine.
He and Mellins both said the results could have practical use, too. For one, researchers may be able to develop a blood test to help objectively diagnose narcolepsy.
Right now, Watson said, narcolepsy can be difficult to pinpoint, because the most common symptom -- daytime sleepiness -- has far more common causes. The most common, he noted, is simple: Not going to bed early enough.