Tourette's Syndrome (cont.)
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Tourette's Syndrome Causes
Our present understanding is that Tourette's syndrome is a biological disorder of the brain, but the exact reasons for of the tics and the associated disorders that are often seen in persons with Tourette's syndrome are not clear.
Fortunately, Tourette's syndrome is not a fatal condition; hence, there are very few possibilities of performing autopsies on individuals with Tourette's syndrome. In the few autopsies reported most of the abnormalities were seen in an area deep in the brain, the basal ganglia, which is known to be strongly associated with the control of movement. This is an expected finding since this area of the brain is known to be abnormal in other conditions that are also associated with movement disorders not related to Tourette's syndrome. Recently, MRI studies of the brain in persons with Tourette's syndrome also have shown some abnormalities in this area of the brain.
There is a familial incidence of Tourette's syndrome. First-degree relatives of persons with Tourette's syndrome more frequently have tics and obsessive compulsive disorders or attention deficit hyperactivity disorder (ADHD) than the general population. Also, twin studies have shown that identical twins (monozygotic twins) are five times more likely to both have Tourette's syndrome than in twins that are not identical (dizygotic twins). These observations suggest an autosomal dominant inheritance of the condition with variable penetrance.
However, in spite of this strong evidence of genetic involvement, at the present time, no gene has been identified as related to Tourette's syndrome. Moreover, other factors are certainly also responsible for the symptoms. For example, the severity of the syndrome in affected identical twins is not necessarily the same. For example, Tourette's syndrome is more severe in the twin who experienced greater perinatal complications.
The observation of tics developing after streptococcal infections motivated clinical trials to look at the role of autoimmune disorders as a cause of Tourette's syndrome. It is known that streptococcal infections can trigger, in certain individuals, autoimmune disorders that can attack and damage the basal ganglia, resulting in Sydenham chorea. This is a movement disorder characterized by multiple abnormal movements, including tics, as well as other behavioral issues such as obsessive compulsive disorders, which are also seen in people with Tourette's syndrome. Also clinical trials have looked at the role that pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections (PANDAS) may play in the development and prognosis of Tourette's syndrome, but, presently, this is only a hypothesis and has not been proven.
Finally studies are inconclusive about the possible association between exposure to stimulants methylphenidate (Ritalin, Ritalin SR, Ritalin LA), amphetamines (Adderall) and certain other medications lamotrigine (Lamictal) and the precipitation of Tourette's syndrome.
It has also been found that Tourette's syndrome is more common in boys than in girls by a ratio of five to one.
Tourette's syndrome has been described in people of many ethnic backgrounds. At the present time there is no indication that Tourette's syndrome is more frequent in any particular ethnic group.
Norberto Alvarez, MD