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). The gene discussed is TPH2; the disease is impulse control disorder.