Dopamine transporter (DAT) single-photon emission tomography (SPECT) with 123I-N-omega-fluoropropyl-2-beta-carbomethoxy-3-beta (4-iodophenyl) nortropane (123I-FP-CIT) is a widely used diagnostic tool for patients with suspected parkinsonian syndromes such as Parkinson’s disease, PSP, and CBD as an in vivo marker of nigrostriatal neuron loss (Palermo and Ceravolo, 2019). The gene discussed is SLC6A3; the disease is Parkinson disease.