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Rare genetic mutation confirmed as a cause of Tourette Syndrome

Jan 12th 2014 at 7:56 PM

Brain researchers say they have confirmed for the first time that a rare genetic mutation can cause some cases of Tourette syndrome, with the fault disrupting production of histamine in the brain.

The New Haven, CT, researchers at the Yale School of Medicine say the histamine effect "is a cause of the tics and other abnormalities of Tourette syndrome." Tics are repetitive movements and vocal sounds, and they are unwanted and involuntary - they cannot be controlled.

Publishing their research on mice in the journal Neuron, the authors raise the question of investigating treatment of Tourette syndrome by drugs that target histamine receptors in the brain.

Drugs with such a mode of action are already being explored by pharmaceutical companies for the treatment of separate brain disorders, schizophrenia and ADHD.

Information from the national gene database about histamine describes the chemical's role - it is a messenger molecule released by nerves, among other functions.

Current neurological drugs under investigation target a certain gene-encoded histamine receptor known as the histamine H3 receptor.

Christopher Pittenger, of the Yale Child Study Center and associate professor of psychiatry and psychology, says of his particular study on histamine genetics:

"These findings give us a new window into what's going on in the brain in people with Tourette. That's likely to lead us to new treatments."

Histamine also has an important role in inflammation, which is why antihistamines work to reduce allergy symptoms. Interactions with the histamine system in the brain, say the Yale researchers, "explain why some allergy medications cause people to feel sleepy."

The specific gene in this study is called HDC (the histidine decarboxylase gene), which the researchers previously found to be mutated in a family that had nine members with Tourette syndrome.
Mouse with glass containers
Researchers found that mice with a faulty HDC gene showed symptoms similar to those found in Tourette syndrome.

That earlier finding of a faulty gene led the authors to confirm its effects on histamine in their present study with mice.

Mice with the same mutation carried by the Tourette family developed symptoms similar to those found in the syndrome, the Yale team showed, saying that this helps to prove that the histamine disruption can cause the tics.
Brain structures and chemicals

The study also found effects to do with dopamine, another brain chemical involved in communication between nerve cells.

There were abnormalities in dopamine neurotransmitter signaling in mice and in the patients carrying the faulty HDC gene.

The disruption was to dopamine effects in the basal ganglia, which is a network of structures responsible for movement - and the part of the brain that Dr. Pittenger focuses on toward the scientific understanding of neuropsychiatric diseases.

His research biography says:

"The basal ganglia are involved both in motor control and in the formation of habits.

Abnormalities in this circuit are implicated in a variety of conditions characterized by maladaptive, inflexible behaviors - habits gone bad.

These include obsessive-compulsive disorder, Tourette syndrome, and drug addiction."

The Tourette Syndrome Association of America - a non-profit whose mission "is to identify the cause of, find the cure for, and control the effects of Tourette Syndrome" - helped to fund the Yale study, which also received financial support from the Allison Family Foundation and the National Institutes of Health.

The US Centers for Disease Control and Prevention (CDC) does not have a firm estimate of the number of people affected by Tourette syndrome in America, but has run studies that indicate a prevalence of between 3 and 6 children out of every 1,000 in the population.

Other researchers, from the Massachusetts General Hospital and the University of Chicago, have also found family genetics behind Tourette's - and obsessive compulsive disorder (OCD), too. Their PLOS Genetics study published in October 2013 found insights into genetic architecture.



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