BY TOM VALEO
For decades, circumstantial evidence has suggested that some people have a genetic susceptibility to narcolepsy, which produces excessive daytime sleepiness, cataplexy, and sleep abnormalities. However, unlike narcoleptic dogs, which lack a receptor for hypocretin (a hormone that promotes wakefulness), humans predisposed to narcolepsy seem to require an environmental trigger that somehow damages or destroys the 70,000 or so brain cells that produce hypocretin.
Now researchers at the Stanford University School of Medicine have found compelling evidence that human narcolepsy is an autoimmune disease that results when people with certain gene variants are exposed to a virus or a vaccine that induces the body to launch an attack on hypocretin-producing cells.
Also, signs of this autoimmune attack appear very early in the course of the disease, which may enable a prompt diagnosis with a simple blood test that would allow treatment to begin sooner, according to veteran sleep researcher Emmanuel Mignot, MD, PhD, director of the Stanford Center for Sleep Sciences and Medicine, the lead author of the study published in the Dec. 18 issue of Science Translational Medicine.
“With a blood test we might be able to diagnose milder cases of narcolepsy and do immune suppression before it’s too late,” said Dr. Mignot, who is also the Craig Reynolds professor of sleep medicine at the Stanford School of Medicine.
The research also provides the first evidence in vivo that autoimmune disease results from molecular mimicry, in which a virus or a bacterium displays molecules so similar to those found in the body’s own tissues that the immune system attacks both.
“This is a huge finding both for narcolepsy and for immunology in general,” Dr. Mignot said. “People have suspected for a long time that molecular mimicry was involved in autoimmune disease, but now we have demonstrated that the immune system sometimes gets confused and fails to distinguish self from virus. I think narcolepsy will become a model for other autoimmune disorders.”
See what sleep experts had to say about this research in the Feb. 6 issue of Neurology Today. For now, browse our archives on sleep disorders: http://bit.ly/1njZKYc.