• Tics are brief movements (motor tics) or sounds (vocal tics) that occur intermittently and unpredictably out of a background of normal motor activity. Although tics can appear as the result of direct brain injury (so-called symptomatic, eg, from head trauma or encephalitis), they most commonly are idiopathic and are part of the spectrum of Gilles de la Tourette syndrome or other idiopathic tic disorders. To aid investigators searching for the gene(s) causing Tourette syndrome, criteria are proposed to classify the idiopathic tic disorders. Although some of these separate entities may ultimately be shown to be caused by the same gene, until that is established, it is considered best when searching for the Tourette's gene to have tic disorders classified into distinct, homogeneous entities. The proposed classification will likely change over time as better diagnostic techniques become available and can both expand and consolidate, particularly after the Tourette gene is located.
Definitions and Classification of Tic Disorders. Arch Neurol. 1993;50(10):1013–1016. doi:10.1001/archneur.1993.00540100012008
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