The most widely used is dopamine transporter single-photon emission CT (DAT-SPECT), which can reveal reduced striatal dopaminergic innervation years before clinical PD. Prodromal individuals (e.g., those with iRBD or leucine-rich repeat kinase 2 (LRRK2) mutations) often have abnormal DAT scans in advance of symptoms [9]. The gene discussed is SLC6A3; the disease is Parkinson disease.