What causes Tourette's syndrome?
Most people with Tourette's syndrome are believed to have a gene that makes them more likely to develop the condition. However, that gene has not been identified. Other factors, such as emotional and physical health or external stress, may also contribute to the development of Tourette's syndrome. Genetic studies indicate tic disorders, including Tourette syndrome, are inherited as a dominant gene(s) that may produce varying symptoms in different family members.
A person with Tourette syndrome has about a 50% chance of passing the gene(s) to one of his/her children. However, the gene(s) may express as Tourette syndrome, as a milder tic disorder, or as obsessive compulsive symptoms with no tics at all. It is known that a higher than usual incidence of milder tic disorders and obsessive compulsive behaviours are more common in the families of Tourette syndrome patients. The sex of the child also influences the expression of the gene(s). The chance that the child of a person with Tourette syndrome will have the disorder is at least three times higher for a son than for a daughter. Yet only a minority of the children who inherit the gene(s) will have symptoms severe enough to ever require medical attention. In some cases, Tourette syndrome may not be inherited; these cases are identified as "sporadic" Tourette syndrome because a genetic link cannot be found.
Research shows that, in Tourette syndrome, something is wrong with the way in which the brain produces or uses important substances called neurotransmitters, which control how signals are sent along the nerve cells. The neurotransmitters dopamine and serotonin have been implicated in Tourette syndrome; noradrenaline is thought to be the most important stimulant. (Medications that mimic noradrenaline may cause tics in susceptible patients.) Whatever the exact defect, it is handed down through the genes from parents to children. If one parent has Tourette syndrome, each child has a 50% chance of getting the abnormal gene. Seven of every ten girls who inherit the gene, and nearly all boys who inherit it, will develop symptoms of Tourette syndrome. Overall, about one in every 2,500 persons has full-blown Tourette syndrome. Three times as many will have some features, usually chronic motor tics or obsessive thoughts. Patients with Tourette syndrome are more likely to have trouble controlling their impulses, to have dyslexia (or other learning problems), and to talk during sleep or wake frequently. Compulsive behavior, such as constantly washing the hands or repeatedly checking that a door is locked, is a common feature of Tourette syndrome, seen in 30-90% of all patients.