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10-09-2009, 09:26 AM
Tourette syndrome (TS) is a childhood neuropsychiatric disorder characterized by motor and phonic (vocal) tics. It is often associated with behavior disorders, particularly obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD). These behavior disorders often accompany the tics and may dominate the clinical picture in some patients. TS is a genetic condition that runs in families . However, the precise genetic abnormality responsible for the phenotype has not yet been elucidated.

The precise pathophysiologic mechanisms of TS are yet to be determined. Most studies support the hypothesis that TS is an inherited developmental disorder of synaptic neurotransmission. Further studies are needed to elucidate the physiologic and cellular mechanisms underlying tics and TS.

The basal ganglia, particularly the caudate nucleus and the inferior prefrontal cortex, are implicated in the pathogenesis of TS. Volumetric magnetic resonance imaging studies have shown that children with TS have larger dorsolateral prefrontal regions as well as increased cortical white matter in the right frontal lobe.

The neurobiology of TS is currently accepted to involve the likely disinhibition in cortico-striatal-thalamic-cortical loops, with an overly active caudate nucleus. Similar models have been ascribed to ADHD and OCD. Dysfunction within these circuits results in an inability to suppress unwanted movements, behaviors, or impulses.

Functional neuroimaging studies performed while patients are actively having tics also demonstrate multifocal activation within the brain, involving the following areas:


Medial and lateral premotor cortices
Anterior cingulated cortex
Dorsolateral-rostral prefrontal cortex
Inferior parietal cortex
Putamen
Caudate nucleus
Primary motor cortex
Broca area
Superior temporal gyrus
Insula
Claustrum


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