Striatal dopamine transporter (DAT) imaging using 123I-ioflupane single photon positron emitted computed tomography (SPECT) (DaTScan, GE) identifies 5−20% of newly diagnosed Parkinson’s disease (PD) subjects enrolling in clinical studies to have scans without evidence of dopaminergic deficit (SWEDD). This evidence concerns the gene SLC6A3 and Parkinson disease.