Causes of Tourette Syndrome

The cause of Tourette Syndrome has not been fully established but a lot has been learnt over the last 20 years. It is known as a neuro-developmental condition, as a vulnerability to having tics seems to develop as the brain is developing, although tics usually first appear at around the age of 5 (can be younger or much older than this). TS is often associated with ‘comorbid’ (also present) conditions such as Attention Deficit Hyperactivity Disorder (ADHD) and Obsessive-Compulsive Disorder (OCD). These conditions often overlap and run in families.

The brain

Brain scanning in people with TS has shown that there are some parts of the brain that function differently or have a slightly different size e.g. some of the structures in the motor circuits that control movement.

There is probably an imbalance in the function of brain neurotransmitters (chemical messengers in the brain that send signals between nerve cells) including dopamine, and probably others. Many of the drugs that reduce tics act by supressing the dopamine system.  Go to our page on medication for further information.

Genetic factors

Although tics often run in families there is not a single gene that causes TS or can be tested to diagnose it. This is different to other genetic diseases such as Huntington’s disease or cystic fibrosis in which only one abnormal gene causes the disease. Research in recent years has focussed on identifying many variations in genes that together increase the risk of an individual developing TS. Thousands of people with TS have contributed to this work, and the results will become more useful with even greater numbers. Identifying which genes contribute to TS should increase our understanding of how the condition develops and may ultimately lead to new treatments, but this is a long process.  Read our guide (far right) on genetics and TS for further information. 

Environmental factors

It is likely that genetic make-up is not the only cause of TS. Other causes are called environmental, meaning that factors in the environment as the brain is developing may influence the risk of developing tics. It is likely that environmental factors interact with an individual’s genetic make-up to determine the risk. A large study which followed up over 6000 pregnant mothers and their children over time found that the strongest risk factor was inadequate weight gain of the mother during pregnancy, but not low birth weight or prematurity of the baby. In addition, use of cannabis and alcohol during pregnancy, and whether the child was the first born were also associated with a higher risk of the child developing TS.  Like the hunt for genetic causes, better information comes from studying large numbers of patients but this can be difficult to interpret and results across different studies have varied.

Another possible factor that may trigger  TS or make it worse is infection. It is not unusual for people with TS to report worse tics during any kind of infection. There has been a theory that a particular kind of infection, with a bacteria called streptococcus, may be particularly important. This has been very difficult to prove as streptococcus throat infections are very common in children.

A major Europe-wide research project called EMTICS is investigating this link. This study includes an investigation into antibiotic treatment of the infection. Results are not yet available and there is no good evidence currently to use antibiotics in TS in most circumstances.

An area related to looking at infection in cases of TS is the special case of children who have a very sudden onset of symptoms associated with streptococcus infection, a condition called Paediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcal infections (PANDAS). For more information on this topic see our section on PANDA and PANS (far right)

This information was written by Dr Jeremy Stern, Dr Helen Simmons, Professor Eileen Joyce and Professor Andrea Cavanna, December 2018.