By using a D2-receptor and vesicular monoamine transporter (VMAT2) ligands as a marker for dopamine receptor integrity in the cortex and striatum respectively, Christopher et al. demonstrated that cognitive impairment in PD is associated with D2 receptor reduction in the insular cortex, anterior cingulate gyrus and parahippocampal gyrus compared to cognitively intact PD controls. This evidence concerns the gene SLC18A2 and Parkinson disease.