Currently, no treatment is available for Parkinson’s disease and the prescribed drugs only allow the control of some symptoms: levodopa (a precursor of dopamine), dopamine receptor agonists, inhibitors of monoamine oxidase B (MAO-B), catechol-O-methyltransferase (COMT) inhibitors, amantadine (an anti-influenza drug widely used in parkinsonism and dyskinesia), and anticholinergic drugs, including antidepressant drugs [89]. The gene discussed is COMT; the disease is drug-induced dyskinesia.