DEFINITIONS AND CLASSIFICATION OF TIC DISORDERS

Tics are brief movements (motor tics) or sounds (vocal tics) that occu r intermittently and unpredictably out of a background of normal motor activity. Although tics can appear as the result of direct brain inju ry (so-called symptomatic, eg, from head trauma or encephalitis), they most commonly are idiopathic and are part of the spectrum of Gilles d e la Tourette syndrome or other idiopathic tic disorders. To aid inves tigators 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 sear ching for the Tourette's gene to have tic disorders classified into di stinct, 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.