Recently, the spectrum of monoaminergic ICD candidate genes was expanded through the identification of a polymorphism in OPRK1, which encodes an opioid receptor, as the strongest genetic predictive factor in a clinical–genetic model designed to predict the occurrence of ICDs in early PD in the Parkinson’s Progression Markers Initiative (PPMI) cohort (12). The gene discussed is OPRK1; the disease is Parkinson disease.