SLC18A2 and Parkinson disease: This could occur, for instance: (i) by an abnormal upregulation/increased activity of hTyr or other putative NM-producing enzymes, such as tyrosinase-related protein 2 (i.e. dopachrome tautomerase), the expression of which we found significantly increased in induced pluripotent stem cell (iPSC)-derived DA neurons from PD patients;71 or (ii) by increased cytosolic DA levels, which may convert to NM, as a consequence of defects in VMAT2-dependent DA encapsulation within synaptic vesicles, as it has been shown in early PD cases26.