They are faster than average for their age on timed tests of motor coordination, and constant tic suppression may lead to an advantage in switching between tasks because of increased inhibitory control.Learning disabilities may be present, but whether they are due to tics or comorbid conditions is controversial; older studies that reported higher rates of learning disability did not control well for the presence of comorbid conditions. There are often difficulties with handwriting, and disabilities in written expression and math are reported in those with TS plus other conditions. Causes
The exact cause of Tourettes is unknown, but it is well established that both genetic and environmental factors are involved. Genetic epidemiology studies have shown that Tourettes is highly heritable, and 10 to 100 times more likely to be found among close family members than in the general population. The exact mode of inheritance is not known; no single gene has been identified, and hundreds of genes are likely involved. Genome-wide association studies were published in 2013 and 2015 in which no finding reached a threshold for significance; a 2019 meta-analysis found only a single genome-wide significant locus on chromosome 13, but that result was not found in broader samples. Twin studies show that 50 to 77% of identical twins share a TS diagnosis, while only 10 to 23% of fraternal twins do. But not everyone who inherits the genetic vulnerability will show symptoms.
ADHD may also contribute to higher rates of anxiety, and aggression and anger control problems are more likely when both OCD and ADHD co-occur with Tourettes.Compulsions that resemble tics are present in some individuals with OCD; "tic-related OCD" is hypothesized to be a subgroup of OCD, distinguished from non-tic related OCD by the type and nature of obsessions and compulsions. Compared to the more typical compulsions of OCD without tics that relate to contamination, tic-related OCD presents with more "counting, aggressive thoughts, symmetry and touching" compulsions. Compulsions associated with OCD without tics are usually related to obsessions and anxiety, while those in tic-related OCD are more likely to be a response to a premonitory urge. There are increased rates of anxiety and depression in those adults with TS who also have OCD.Among individuals with TS studied in clinics, between 2.9% and 20% had autism spectrum disorders, but one study indicates that a high association of autism and TS may be partly due to difficulties distinguishing between tics and tic-like behaviors or OCD symptoms seen in people with autism.Not all people with Tourettes have ADHD or OCD or other comorbid conditions, and estimates of the rate of pure TS or TS-only vary from 15% to 57%; in clinical populations, a high percentage of those under care do have ADHD. Children and adolescents with pure TS are not significantly different from their peers without TS on ratings of aggressive behaviors or conduct disorders, or on measures of social adaptation.