Several studies have reported an association between ICD development in PD patients and genetic polymorphisms in dopamine receptor (DRD1–3) and glutamate receptor (GRIN2B) genes (6–9), while individual studies also point toward a potential association with genetic polymorphisms in serotonin receptor (HTR2A), dopamine transporter (DAT1), and tryptophan hydroxylase 2 (TPH2) genes (10, 11). Here, DRD1 is linked to Parkinson disease.