SLC6A3 and Parkinson disease: The prodromes of Parkinson's disease (PD) can begin many years before diagnosis1, 2 and offer an opportunity to identify individuals in the earlier stages of the disease.3 Studies aiming to identify patients at risk of PD have mainly centred on individuals with a family history of PD or asymptomatic carriers of genes associated with PD, idiopathic anosmia, rapid eye movement–sleep behavior disorder (RBD), or with imaging abnormalities associated with increased risk (such as hyperechogenicity on transcranial sonography and nigrostriatal deficit on dopamine transporter imaging).4, 5, 6, 7