Tic disorders are transient or chronic conditions associated with difficulties in self-esteem, family life, peer acceptance, or school or job performance that are related directly to the presence of motor or phonic tics. Although descriptions of tic symptoms have appeared since antiquity, the systematic study of individuals with tic disorders dates only from the 19th century with the reports of Itard<sup>56 Itard J.M.G. Memoire sur quelques fonctions involontaires des appareils de la locomotion de la prehension et de la voix Arch Gen Med 1825 ;  8 : 385

Cliccare qui per andare alla sezione Riferimenti</sup> and Gilles de la Tourette.<sup>39 Gilles de la Tourette G. Ètude sur une affection nerveuse caractérisée par de l'incoordination motrice accompagnée d'echolalie et de copralalie Arch Neurol 1885 ;  9 : 19-158

Cliccare qui per andare alla sezione Riferimenti</sup> Tourette, in his classic study of 1885, described nine cases of chronic tic disorder characterized by motor “incoordinations” or tics, “inarticulate shouts accompanied by articulated words with echolalia and coprolalia.” In this report, he described not only the cardinal features of severe tic disorders, he also noted the association between tic disorders and obsessive–compulsive symptoms as well as the hereditary nature of the syndrome in some families.

Individuals with tic disorders also may present with a complex array of behavioral difficulties including disinhibited speech or conduct, impulsivity, distractibility, motoric hyperactivity, and obsessive–compulsive symptoms. Professional opinion has been divided on how broadly to define the spectrum of maladaptive behaviours associated with Tourette's syndrome. This controversy is fueled, in part, by the genuine frustration that parents, educators, and other professionals encounter when they attempt to divide an individual child's repertoire of problem behaviors into those that are “Tourette-related” and those that are not. Population-based epidemiologic studies and family-genetic studies have begun to clarify these issues, but much work remains to be done.

In this article, a brief discussion of the phenomenology and classification of tic disorders precedes a review of the causes, neurobiologic substrates, assessment, and management of these conditions. The general perspective that is presented is that Tourette's syndrome and other etiologically related disorders including some forms of obsessive–compulsive disorder are model neurobiologic disorders in which it may be possible to understand the genetic and environmental (epigenetic) mechanisms that interact to produce syndromes of varying severity. Advances in understanding the causes and determinants of tic disorders may lead to the development of more rational and effective interventions.