COMT and Parkinson disease: Diagnosis is based on clinical signs and symptoms, and various therapeutic options available for the treatment of Parkinson's disease include dopamine agonists, levodopa, anticholinergic agents, monoamine oxidase inhibitors, catechol-o-methyltransferase inhibitors, and amantadine [6]. Levodopa is the most effective treatment for Parkinson's disease combined with carbidopa to inhibit the peripheral conversion to dopamine [7].