Positron emission tomography (PET) approaches have indicated decreased D2R binding (Steeves et al., 2009; Stark et al., 2018) and relatively unchanged D1R binding in the ventral striatum in PD + ICD (Payer et al., 2015) compared with PD patients without ICDs (PD-ICD). This evidence concerns the gene DRD2 and impulse control disorder.