Tourette syndrome results from a combination of genetic, neurological, and environmental factors, not any single cause. No one gene or event triggers it on its own. Instead, inherited vulnerability interacts with differences in brain chemistry and, in some cases, prenatal exposures to produce the motor and vocal tics that define the condition. About 1 in 162 children have Tourette syndrome, with boys roughly three times more likely to be affected than girls.
Genetics Play the Largest Role
The strongest evidence points to genetics. Twin studies show that when one identical twin has Tourette syndrome, the other twin also has it 53% of the time. For non-identical twins, that number drops to just 8%. That gap tells researchers that inherited DNA accounts for a large share of risk, though the fact that identical twins don’t match 100% of the time confirms that genes alone aren’t the full story.
Two specific genes have stood out in large-scale genetic studies. One, called SLITRK1 on chromosome 13, helps guide how nerve cells connect during brain development. The other, HDC on chromosome 15, is involved in producing histamine, a chemical messenger in the brain. Both appear to be genuinely linked to tic disorders. Beyond these, however, no other individual gene mutations have been confirmed as clearly disease-causing. Most researchers now believe Tourette syndrome involves many common gene variants, each contributing a small amount of risk, rather than one or two rare mutations.
A Misfiring Circuit in the Brain
The tics in Tourette syndrome trace back to a loop of brain structures that normally helps you start, stop, and fine-tune movements. This loop connects the basal ganglia (a set of deep brain structures that act as a gatekeeper for movement), the thalamus (a relay station), the cerebellum (which coordinates timing and precision), and the motor areas of the cortex (which send the final “move” signal to your muscles).
In people with Tourette syndrome, a small area within the basal ganglia becomes abnormally excitable. That excess activity throws off the gatekeeper function: signals that should be suppressed instead pass through the thalamus and reach the cortex, producing an involuntary movement or sound. Brain imaging studies consistently show that these circuits are more tightly connected and more active in people with tics, and recent work has also found abnormal activity in the cerebellum during tic episodes, suggesting the problem extends beyond the basal ganglia alone.
Neurotransmitter Imbalances
The chemical messengers that carry signals through these brain circuits are also out of balance. Dopamine, the neurotransmitter most associated with movement and reward, appears to be the central player. People with Tourette syndrome show heightened sensitivity of dopamine receptors in the basal ganglia, which helps explain why medications that dial down dopamine activity can reduce tics.
Two other neurotransmitters matter as well. Glutamate, the brain’s main “go” signal, appears overactive in the motor circuits involved in tics, while GABA, the brain’s main “stop” signal, appears underactive. That combination tips the balance toward too much excitation and not enough inhibition, making involuntary movements more likely. These glutamate and GABA imbalances don’t operate in isolation; they interact with dopamine circuits, amplifying the overall effect.
Serotonin, which influences mood and impulse control, may also play a role, particularly in the obsessive-compulsive and anxiety symptoms that frequently accompany Tourette syndrome. Its exact contribution to tics themselves remains less clear.
Prenatal and Birth Complications
What happens before and during birth can influence whether someone with genetic vulnerability actually develops tics, and how severe those tics become. The two most consistently reported prenatal risk factors are maternal smoking during pregnancy and low birth weight.
Maternal smoking has been linked not only to a higher chance of developing Tourette syndrome but also to greater tic severity and more severe co-occurring ADHD and OCD symptoms. In twin studies where only one twin developed Tourette syndrome, the affected twin tended to be the one with lower birth weight. The correlation was strikingly direct: the greater the weight difference between twins, the greater the difference in their tic severity scores.
Pregnancy complications like high blood pressure, infections, preeclampsia, and severe nausea have also been associated with worse tic severity. Delivery complications, including premature membrane rupture and signs of fetal distress, similarly predicted more severe tics later in childhood. These factors likely don’t cause Tourette syndrome outright but can push a genetically predisposed child toward more noticeable symptoms.
The Immune System Connection
A more controversial line of research explores whether infections, particularly strep throat, can trigger sudden-onset tics in some children. The idea, first proposed in 1998 under the name PANDAS (Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections), suggests that the immune response to strep bacteria can mistakenly attack brain tissue in the basal ganglia, producing tics or obsessive-compulsive symptoms.
The evidence is mixed. Some case-control studies found that children with OCD and tic disorders were 2 to 13 times more likely to have had a recent strep infection than children without these conditions. A large Danish study tracking over a million children found a modestly higher rate of tic disorders and OCD in those who tested positive for strep. But other studies found no clear link between strep infections and the sudden appearance or worsening of tics. Notably, in the Danish study, even children who tested negative for strep but were tested anyway (suggesting they were sick with something) had a slightly elevated risk, raising the possibility that general immune activation, not strep specifically, could be a factor.
PANDAS remains a real diagnosis in clinical practice, but it likely explains only a small subset of tic cases rather than Tourette syndrome broadly.
How These Factors Come Together
Tourette syndrome is best understood as a threshold condition. A child inherits a collection of gene variants that make their brain’s movement-control circuits more excitable than average. Prenatal exposures like smoking or low birth weight may lower that threshold further. Once the threshold is crossed, the dopamine-sensitive circuits in the basal ganglia begin producing tics, typically between ages 4 and 6. Tic severity usually peaks between ages 10 and 12, then declines during adolescence for most people.
This layered model also helps explain why Tourette syndrome so rarely appears alone. Roughly 86% of people with the condition have at least one other neuropsychiatric diagnosis. ADHD is the most common, affecting 60 to 80% of people with Tourette syndrome. OCD occurs in 11 to 80% depending on how broadly it’s defined. Mood disorders, anxiety, and disruptive behavior each show up in about 30% of cases. These aren’t coincidences. The same genetic variants and circuit abnormalities that produce tics overlap heavily with the brain systems involved in attention, impulse control, and anxiety. For many people, managing these co-occurring conditions matters as much as, or more than, managing the tics themselves.