Rare Mutation Identified for Tourette Syndrome
Neurology Today:
17 June 2010 - Volume 10 - Issue 12 - pp 1,12
doi: 10.1097/01.NT.0000383479.76782.a7

ARTICLE IN BRIEF
The finding of a rare mutation in the gene involved with the histamine system in a father and eight of his children with Tourette syndrome (TS) point to a role for histaminergic neurotransmission in the mechanism and modulation of TS and tics.Doctors usually treat the symptoms of Tourette syndrome (TS) with dopamine blockers aimed at suppressing tics. But a new study points to a rare mutation in a gene involved in the histamine system, which researchers say could lead to new developments in treating and understanding the disease.The study, published in the May 20 issue of the New England Journal of Medicine, looked at one family where the father and all eight children were diagnosed with TS.

Although all the children had the neurological disorder, the mother did not carry the mutation, said Matthew W. State, MD, PhD, co-director for the Program on Neurogenetics and deputy chairman for research in the Department of Psychiatry at Yale University School of Medicine.Researchers mapped the 51 genes in the region, looking at each one to find a mutation that might be responsible for TS in the family, said Dr. State. They were looking for large-scale chromosomal abnormalities in the 51 known genes in the region, but they were originally expecting affected patterns to be located in the dopaminergic system.

“There were many other genes in the interval that we considered more likely suspects and tested first,” Dr. State said. “But when we finally found the rare mutation in the HDC [encoding 1-histodine decarboxylase] and started looking at the literature [on the role of the mutation in animal models of TS], it was clear we should have placed this gene at the top, not the bottom of our list.”“Given that Tourette's syndrome has a population prevalence of 1 percent and a rate of recurrence of 10 to 15 percent among first-degree relatives of an affected person, it is extremely unlikely that all eight offspring of an affected parent would have Tourette's syndrome by chance, suggesting that this kindred indeed carries a mendelian form of the syndrome,” the authors wrote.

The findings, together with previously published data from animal models of TS, point to a role for histaminergic neurotransmission in the mechanism and modulation of TS and tics, Dr. State said. There is a large body of prior evidence showing its function in regions of the brain involved in movement disorders, including the striatum and cortex, areas of the brain usually implicated in TS.In mouse studies, he added, decreased brain histamine has led to an increase in stereotypic behaviors — rearing, sniffing, and biting — that appear similar to human tics. In addition, highly selective antagonist and inverse agonists increase histaminergic neurotransmission and decrease these behaviors in mice.

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