SLC18A2 and Parkinson disease: It has been deduced that VMAT2 dysfunction can lead to a reduction of dopamine in vesicles and further intracellular accumulation of dopamine-generated toxic products, ultimately resulting in the degeneration of dopaminergic neurons, particularly in the striatum, which is responsible for PD symptoms (Olanow and Tatton, 1999; Pifl et al., 2014).