In the small hours of the night, up to 20% of sleeping children and 3% of sleeping adults get busy, wandering the house, dancing, or cake-baking. Researchers have now identified a gene of the immune system that may explain sleepwalking. The find also adds weight to a controversial theory linking sleep disorders with a disruption of the immune system.
Because the children of sleepwalkers are 10 times more likely to somnambulate than those without sleepwalking relatives, researchers have long suspected that the disorder has a genetic component. Geneticist Mehti Tafti of Geneva University, Switzerland, and his colleagues wondered if a gene implicated in other sleeping disorders such as narcolepsy might be a culprit. To find out, his group compared the gene, called HLA-DQB1, in 60 sleepwalkers and their immediate families, along with 60 non-sleepwalkers.
Sure enough, the risk of sleepwalking was 3.5 times higher in people carrying a particular version of the gene, the team reports in the January issue of Molecular Psychiatry. The HLA genes help target foreign cells for attack by the immune system. Tafti favors the idea that severe sleepwalking might be due to the immune system targeting cells important for sleep regulation, an idea supported by the other known genetic links between sleep disorders and HLA genes. If true, this could lead to a complete revamping of the treatment of sleep disorders which currently treats only the symptoms, says Tafti. He adds that these experiments must now be replicated using the extended families of sleepwalkers to test how well the disease can be predicted by HLA variation.
The team's findings are "remarkable and suggestive of an autoimmune mechanism" of sleepwalking disorder, says Jan Born, a neuroendocrinologist at the University of Luebeck, Germany, "however, this is a highly speculative conclusion." Born points out that changes in the immune systems of sleepwalkers have not been observed, although these HLA variations might be affecting only a small and highly specific group of immune cells yet to be discovered.