CYP2D6 and Parkinson disease: Based on initial reports on an increased occurrence of PD in CYP2D6 PMs as well as a higher incidence of activity-decreasing SNPs in CYP2E1 of PD patients (McCann et al., 1997; Vaglini et al., 2004), we first analyzed the distribution of SNPs in these two genes in PD patients and HC.