SLC6A3 and Parkinson disease: Cross-sectional single photon emission computed tomography and positron emission tomography studies on the dopamine transporter (DAT) - that clears dopamine from the synaptic cleft after its release - have consistently shown reduced striatal DAT availability in PD + ICD compared with PD − ICD (Cilia et al. 2010; Lee et al. 2014; Voon et al. 2014).