Levels of VMAT2 are reduced in the striatum of PD brain samples (Miller et al. 1999) and in positron emission tomography (PET) studies on PD patients (Kilbourn et al. 1993; Frey et al. 1996; Lee et al. 2000; Martin et al. 2008; Okamura et al. 2010). This evidence concerns the gene SLC18A2 and Parkinson disease.