Neurobiology of Tourette syndrome: Current status and need for further investigation

Tourette syndrome (TS) is a common, chronic neuropsychiatric disorder characterized by the presence of fluctuating motor and phonic tics. The typical age of onset is ~5-7 years, and the majority of children improve by their late teens or early adulthood. Affected individuals are at increased risk for the development of various comorbid conditions, such as obsessive- compulsive disorder, attention deficit hyperactivity disorder, school problems, depression, and anxiety. There is no cure for tics, and symptomatic therapy includes behavioral and pharmacological approaches. Evidence supports TS being an inherited disorder; however, the precise genetic abnormality remains unknown. Pathologic involvement of cortico-striatal-thalamo-cortical (CSTC) pathways is supported by neurophysiological, brain imaging, and postmortem studies, but results are often confounded by small numbers, age differences, severity of symptoms, comorbidity, use of pharmacotherapy, and other factors. The primary site of abnormality remains controversial. Although numerous neurotransmitters participate in the transmission of messages through CSTC circuits, a dopaminergic dysfunction is considered a leading candidate. Several animal models have been used to study behaviors similar to tics as well as to pursue potential pathophysiological deficits. TS is a complex disorder with features overlapping a variety of scientific fields. Despite description of this syndrome in the late 19th century, there remain numerous unanswered neurobiological questions.