SLC6A3 and Parkinson disease: The classic method of differentiating PD tremor from ET involves iodine-123-labelled N-omega-(flu-oropropyl)-2beta-carbomethoxy-3beta-(4-iodophenyl) tropane and iodine-123-labelled 2β-carbomethoxy-3β-(4-iodophenyl) tropane dopamine transporter imaging with single-photon emission computed tomography using nuclear imaging techniques [51,52,53].