What causes Tourette's disorder?
Tourette's disorder is an autosomal dominant disorder. Autosomal means that both males and females are affected, and dominant means that 1 copy of the gene is necessary to have the condition. This means that a parent with TD or a parent who has the gene for TD has a 50/50 chance, with each pregnancy, to pass the gene on. TD is associated with a nongenetic cause in 10% to 15% of children. Complications of pregnancy, low birth weight, head trauma, carbon monoxide poisoning, and encephalitis are thought to be associated with the onset of nongenetic TD.
Dominant disorders exhibit something known as incomplete penetrance, which means that not everyone with the gene will have symptoms of Tourette's disorder. In other words, if a parent passes the gene on to a child, the child may not have any symptoms of the disorder. If a daughter inherits the gene, there is a 70% chance that she will have at least 1 of the signs of TD. On the other hand, if a son inherits the gene, there is a 99% chance that he will have at least 1 of the signs of TD.
Finally, dominant disorders can also exhibit something known as variable expressivity. This means that there are differences in the expression of the TD gene in different people. For example, 1 person with TD may have obsessive-compulsive disorder, while another has a chronic tic disorder, while another has full-blown TD. In addition, there are differences in expressivity between males and females: males are more likely to have full-blown TD or chronic tics, while females are more likely to have obsessive-compulsive disorder (OCD), an anxiety disorder in which a person has an unreasonable thought, fear, or worry (obsession) that he or she tries to manage through a ritualized activity (compulsion) to reduce the anxiety.
Who is affected by Tourette's disorder?
A diagnosis of TD is generally made before the child reaches his or her 18th birthday. In the majority of cases, a child is diagnosed around the age of 7. TD affects more males than females.
What are the symptoms of Tourette's disorder?
Tic behaviors seen in TD change over time, and vary in frequency and complexity. The following are the most common tic behaviors associated with TD. However, each child experiences symptoms differently. Symptoms may include:
Involuntary, purposeless, motor movements (may involve different parts of the body, such as the face, neck, shoulders, trunk, or hands):
- Head jerking
- Any excessively repeated movements (for example, foot tapping, leg jerking, or scratching)
Some of the more complex tic behaviors associated with TD may appear purposeful, and may include the following:
- Sticking out the tongue or lip-smacking
- Touching behaviors
- Making obscene gestures
In addition to some, or all, of the above symptoms, TD is also characterized by one or more vocal tics (meaningless sound), in order for a diagnosis of TD to be made, including the following:
- Grunting or moaning sounds
- Tongue clicking
- Throat clearing, snorting, or coughing
- Echoing sounds or phrases repeatedly
Many children and adolescents who have TD also have attention problems and some also have academic difficulties. However, most have normal intelligence and do not usually have primary learning disabilities.
The symptoms of TD may resemble other conditions or medical problems. Always consult your child's health care provider for a diagnosis.