Tourette

Tourette syndrome Classification Characteristics Causes Diagnosis Screening Management Prognosis Epidemiology History and research directions

Causes

The exact cause of Tourette's is unknown, but it is well established that both genetic and environmental factors are involved.[31] Genetic studies have shown that the overwhelming majority of cases of Tourette's are inherited, although the exact mode of inheritance is not yet known,[32] and no gene has been identified.[6] In some cases, Tourette's is sporadic, that is, it is not inherited from parents.[33] In other cases, tics are associated with disorders other than Tourette's, a phenomenon known as tourettism.

A person with Tourette's has about a 50% chance of passing the gene(s) to one of his or her children, but Tourette's is a condition of variable expression and incomplete penetrance.[35] Thus, not everyone who inherits the genetic vulnerability will show symptoms; even close family members may show different severities of symptoms, or no symptoms at all. The gene(s) may express as Tourette's, as a milder tic disorder (transient or chronic tics), or as obsessive compulsive symptoms without tics. Only a minority of the children who inherit the gene(s) have symptoms severe enough to require medical attention.[36] Gender appears to have a role in the expression of the genetic vulnerability: males are more likely than females to express tics.[25]

Non-genetic, environmental, infectious, or psychosocial factors—while not causing Tourette's—can influence its severity.[6] Autoimmune processes may affect tic onset and exacerbation in some cases. In 1998, a team at the US National Institute of Mental Health proposed a hypothesis that both obsessive-compulsive disorder (OCD) and tic disorders may arise in a subset of children as a result of a poststreptococcal autoimmune process.[37] Children who meet five diagnostic criteria are classified, according to the hypothesis, as having Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal infections (PANDAS).[38] This contentious hypothesis is the focus of clinical and laboratory research, but remains unproven.[39][40]

The exact mechanism affecting the inherited vulnerability to Tourette's has not been established, and the precise etiology is unknown. Tics are believed to result from dysfunction in cortical and subcortical regions, the thalamus, basal ganglia and frontal cortex.[31] Neuroanatomic models implicate failures in circuits connecting the brain's cortex and subcortex,[6] and imaging techniques implicate the basal ganglia and frontal cortex.[41]

Some forms of OCD may be genetically linked to Tourette's.[22][42] A subset of OCD is thought to be etiologically related to Tourette's and may be a different expression of the same factors that are important for the expression of tics.[43] The genetic relationship of ADHD to Tourette syndrome, however, has not been fully established.