The left panel of Figure 6 shows that SLC18A1, 2, and 3 may have a role in synaptic vesicle cycling, acetylcholinesterase (ACHE) [42], and amine oxidase [flavin-containing] A (MAOA) [43,44] signaling, which have been shown to be involved in tryptophan metabolism, clycerophospholipid metabolism, and also related to cocaine and amphetamine addiction, as well as alcoholism, and Parkinson’s disease in the presynaptic nerve terminal. This evidence concerns the gene SLC18A1 and Parkinson disease.