COMT and Parkinson disease: Up to the present time, the treatment with the assistance of dopamine (DA) precursor (levodopa), DA agonists, catechol-O-methyltransferase (COMT) inhibitors, and monoamine oxidase B (MAO-B) inhibitors principally focuses on the mitigation of PD-related manifestations, but hitherto no therapeutic candidate has been indicated to totally abolish the progression of the ailment [16,17,18].