A blockade of D1R with a D1R antagonist, SCH23390, significantly enhances the conversion of l-3,4-dihydroxyphenylalanine (l-DOPA) to dopamine in PD patients by augmentation of brain aromatic l-amino acid decarboxylase (AADH) compared with l-DOPA alone, suggesting the further enhancement of dopamine metabolism [9]. This evidence concerns the gene DRD1 and Parkinson disease.