However, because DAT availability in the posterior putamen is already exhausted when patients with PD visit a clinic for motor complaints, it is plausible that dopaminergic mechanisms play a role in the prediagnostic (i.e., preclinical or prodromal) phase of PD, while extra-dopaminergic mechanisms emerge in the clinical phase of PD. Here, SLC6A3 is linked to Parkinson disease.