Radioactive tracers in PD patients have been used to substantiate (1) compromised integrity of pre-synpatic nigrostriatal projections, i.e., [18F]LDOPA (which monitors DA uptake, metabolism, DOPA decarbarboxylase (DDC), DA storage within intact nerve terminals); (2) faulty DA transporters (DAT) i.e., CFT, C-RTI-32, FP-CIT ligands, [11C]methylphenidate (MP)/99mTc-TRODAT-1 or (3) abnormal type-2-vesicular monoamine transporter (VMAT2) function using tracers such as [11C]-dihydrotetrabenazine (DTBZ) which measures cytoplastic DA uptake into synaptic vesicles [28–30]. The gene discussed is SLC6A3; the disease is Parkinson disease.