In terms of PD, the current therapy in practice is applied as a combination of gold-standard dopaminergic reposition with 3-(3,4-dihydroxyphenyl)-l-alanine (l-dopa), along with other agents such as MAO-B, catechol O-methyltransferase (COMT) inhibitors, dopaminergic agonists, and cholinergic blockers [222]. This evidence concerns the gene COMT and Parkinson disease.