New Insights Into Sleeping Disorder Narcolepsy
It may have its roots in immune system problems, study suggests
By Amy Norton
WEDNESDAY, Dec. 18, 2013 (HealthDay News) -- A new study has uncovered evidence that most cases of narcolepsy are caused by a misguided immune system attack -- something that has been long suspected but unproven.
Experts said the finding, reported Dec. 18 in Science Translational Medicine, could lead to a blood test for the sleep disorder, which can be difficult to diagnose.
It also lays out the possibility that treatments that focus on the immune system could be used against the disease.
"That would be a long way out," said Thomas Roth, director of the Sleep Disorders and Research Center at Henry Ford Hospital, in Detroit.
"If you're a narcolepsy patient now, this isn't going to change your clinical care tomorrow," added Roth, who was not involved in the study.
Still, he said, the findings are "exciting," and advance the understanding of narcolepsy.
Narcolepsy causes a range of symptoms, the most common being excessive sleepiness during the day. But it may be best known for triggering potentially dangerous "sleep attacks." In these, people fall asleep without warning, for anywhere from a few seconds to a few minutes.
About 70 percent of people with narcolepsy have a symptom called cataplexy -- sudden bouts of muscle weakness. That's known as type 1 narcolepsy, and it affects roughly one in 3,000 people, according to the U.S. National Institute of Neurological Disorders and Stroke.
Research shows that those people have low levels of a brain chemical called hypocretin, which helps you stay awake. And experts have believed the deficiency is probably caused by an abnormal immune system attack on the brain cells that produce hypocretin.
"Narcolepsy has been suspected of being an autoimmune disease," said Dr. Elizabeth Mellins, a senior author of the study and an immunology researcher at Stanford University School of Medicine, in California.
"But," she said, "there's never really been proof of immune system activity that's any different from normal activity."
Mellins thinks her team has uncovered "very strong evidence" of just such an underlying problem.
The researchers found that people with narcolepsy have a subgroup of T cells in their blood that react to particular portions of the hypocretin protein -- but narcolepsy-free people do not. T cells are a key part of immune system defenses against infection.
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.