Large genetic association and linkage studies to date have failed to implicate genes for dopamine synthesis or metabolism as causes of TS, but clinical presentations of rare genetic diseases involving dopamine pathways are supportive, as in a recently reported case of TS in a girl with chromosome 22q11 deletion [7]. This region contains Catechol-O-Methyltransferase (COMT), which degrades dopamine, norepinephrine, and epinephrine. Low-COMT gene copy number has been associated with obsessive compulsive and hyperactive psychopathology in velocardiofacial syndrome [8], and lesser-COMT activity theoretically could increase catecholamines and hyperkinetic movements.
