COMT and Parkinson disease: For example, the “gold standard” levodopa (L-DOPA) replacement therapy in combination with monoamine oxidase B (MAO-B) and/or catechol-O-methyltransferase (COMT) inhibitors, DA agonists, or DOPA-decarboxylase inhibitors still remains the most widely used treatment of PD [6,7,8].