In early PD patients, levodopa-derived dopamine is packaged into synaptic vesicles by vesicular monoamine transporter 2 (VMAT-2), stored, and released in both tonic and phasic bursts in response to impulse flow [40, 41], in order to preserve dopamine receptors from levodopa plasma concentration fluctuations and, therefore, to maintain physiological dopaminergic transmission [42, 43]. The gene discussed is SLC18A2; the disease is Parkinson disease.