http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=350423 4&dopt=Citation
"A patient with Gilles de la Tourette syndrome later developed Parkinson's disease in middle age. This was accompanied by a marked reduction in the frequency of tics but levodopa toxicity exacerbated the tics. The dopamine hypothesis of tic disorders is supported by this observation"