SLC6A3 and Parkinson disease: Two SNPs in DDC (rs921451 - c.-29+5426A>G and rs3837091 - c.-61_-58delAGAG), one in MAOB (rs1799836 - c.1348-36A>G), and one in SLC6A3 (rs393795 - c.653+4065C>A) were selected due to their previous association with drug response in PD.