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Genetic Study Confirms the Immune System's Role in Narcolepsy -Cataplexy BETHESDA, Md -- May 4, 2009 -- Researchers have identified a gene associated with narcolepsy. The gene has a known role in the immune system, which strongly suggests that autoimmunity, in which the immune system turns against the body's own tissues, plays an important role in the disorder. "The link between narcolepsy and autoimmunity was proposed decades ago, but efforts to verify it have failed repeatedly. Current findings leave little doubt that autoimmunity plays a role," said Merrill Mitler, PhD, National Institute of Neurological Disorders and Stroke (NINDS), Bethesda, Maryland. The study, which appears today in the journal Nature Genetics, focused on narcolepsy with cataplexy. The symptoms of narcolepsy-cataplexy have been shown to result from the death of a small group of brain cells that normally regulate the sleep-wake cycle by releasing chemicals called hypocretins. Genetic and environmental factors both clearly play a role in narcolepsy-cataplexy. Until now, the best evidence for autoimmunity as a cause of the disorder was the discovery that nearly everyone with the disorder has unique variants of a gene called HLA-DQB1*0602. This is one of the genes that encodes HLA proteins, which dot the surface of the body's cells and help the immune system identify foreign proteins. Some researchers theorise that the HLA variants found in people with narcolepsy-cataplexy predispose them to an autoimmune reaction that destroys their hypocretin-producing cells. There are gaps in that theory, however, says Emmanuel Mignot, MD, Center for Narcolepsy, Stanford University School of Medicine, Palo Alto, California. Dr. Mignot discovered the link between narcolepsy and the hypocretins, and helped establish the link to the HLA system. HLA proteins are found in many tissues including the brain, where they may affect brain development, he said. HLA variations, however, do not fully account for narcolepsy-cataplexy. Dr. Mignot led a genome-wide association study to search for other genes associated with narcolepsy-cataplexy. The study included more than 4,000 individuals, all of whom had the HLA variants that predispose to narcolepsy-cataplexy but only about half of whom had the disorder. Participants were from the US and from 8 countries in Europe and Asia. The researchers discovered that in addition to unique HLA variants, people with narcolepsy-cataplexy are also more likely to have unique variants of the TCRA gene, which encodes a receptor protein on the surface of T cells. The findings of Dr. Mignot's group indicate that narcolepsy-cataplexy is linked to autoimmunity and involves T-cells. The research could lead to new approaches to prevention and treatment. One possibility may be preventing the disorder by stopping the effects of the autoimmune process. "If we can define the changes in the T cell receptor associated with narcolepsy-cataplexy, we might be able to develop drugs that block the protein's abnormal activity and prevent the onset of the disorder," said Dr. Mignot. Current treatments such as stimulant drugs for combating daytime sleepiness and antidepressants for cataplexy are only able to control symptoms, and do not address the underlying loss of hypocretin cells. It is important to note that the, like most genome-wide association studies, did not identify genetic variants that directly cause narcolepsy-cataplexy. Instead it identified groups that are more likely to show narcolepsy-cataplexy and groups that are less likely to show the disorder. In people with the HLA variants that predispose to narcolepsy-cataplexy, there is about a 20-fold higher frequency of the disorder if variants in the TCRA gene are present. t is yet to be known which people with the genetic variants will go on to develop narcolepsy-cataplexy. SOURCE: National Institutes of Health E-mail this page to a friend or colleague! To print, use this version