Tourette Sydrome is a neuropsychiatric, childhood-onset disorder characterized my motor tics in addition to vocal (phonic) tics. Original estimates of the prevalence of this condition was that it was very rare. However, it appears that many individuals with the condition has a relatively mild form of the disorder. Including these individuals produces a prevalence rate of between .1% and 1% of the population.
Common motor tics presenting on average around ages 5 to 7 years of age include eye blinking, facial twitching, sniffing and shoulder shrugging. The most common motor tic is throat clearing. Outbursts of shouting profanities is commonly felt to be common in Tourette Syndrome but actually occurs in only 10% of cases.
Ryan Felling and Harvey Singer recently published an excellent overview of the neurobiology of Tourette Sydnrome in The Journal Neuroscience. This review includes an introduction to the syndrome before examining brain circuits, animal models, structural and functional brain imaging findings.
The authors note that brain structural and functional abnormalities in Tourette Syndrome appear diffusely located but do involve the brain stuctures related to motor control including the basal ganglia (See Brain Tutor. There are several known neuropsychiatric conditions of the basal ganglia that produce motor abnormalities.
Parkinson's disease is an abnormality of the basal ganglia's substantia nigra producing slowed motor movements with muscle rigidity. Huntington's disease produces atrophy of the basal ganglia region known as the head of the caudate and is characterized by jerky, uncontrolled movements known as chorea.
The structure and functional brain imaging studies to date in Tourettes Sydrome have demonstrated a variety of effects in the basal ganglia including:
- reduced caudate volume (smaller caudate size linked to greater tic severity)
- enlarged putamen
- activity in putament and caudate (and cortex) correlate with tic activity
- decreased activity in the putamen and caudate with attempts to suppress tic
The review notes that Tourette Syndrome appears to be due to "pathololgic involvement of the cortico-striatal (putamen/caudate)-thalamo-cortico" brain circuits with dysfunction of the neurotransmitter dopamine a key contributor to disorder.
The authors note that no effective treatment exists for Tourette Syndrome. Interventions focus on behavioral and drug treatment with an emphasis on treating the common co-occuring disorders: OCD and ADHD. Thankfully, symptoms often reduce in frequency and severity with age.
The authors conclude significant additional research is needed using larger samples with better description of specific tic patterns, control for comorbid ADHD and OCD and focus on whether brain changes found in Tourette Sydrome are primary or may result from compensatory mechanism in response to tic motor behaviors.
Interested readers can learn more about this disorder from a excellent series of discussion by patients with Tourettes Syndrome from the New York Times Patient Voices Multimedia project here.
Screen Shot of Basal Ganglia Structures from Brain Tutor iPad app.
