CYP2D6 and Parkinson disease: The CYP enzyme debrisoquine 4-hydroxylase encoded by the CYP2D6 gene (MIM: 124030) is of particular importance in the context of PD since it is expressed in neurons and metabolizes endogenous and environmental neurotoxins that have been associated with idiopathic PD [6] Importantly, individuals with PD have lower CYP2D6 expression in the brain [7].