Tourette’s syndrome (also called Gilles de la Tourette syndrome) is a neuropsychiatric disorder that occurs with an estimated prevalence of 1% among school-age children [38], is characterized by multiple chronic tics (involuntary movements and vocalizations) and is often accompanied by other behavioural disorders, including ADHD and obsessive-compulsive disorder (OCD) [34]. Although family and twin studies have suggested a contribution of genetic factors in Tourette’s syndrome, its precise contribution rate remains unclear [39]. Until now, most association studies have focussed on candidate genes belonging to the dopaminergic pathway, and showed several positive associations for the DAT, monoamine oxidase A (MAOA; Xp11.3) and the dopamine receptors D2 (DRD2; 11q23), D3 (DRD3; 3q13.3) and D4 [40-47]. However, since not all subsequent replication studies were positive [48-53] and other genes were found to associate as well [54], the contribution of the dopaminergic pathway to Tourette’s syndrome remains to be established.
