Nevertheless, due to the retrospective study design and the lack of dopamine transporter (DAT) scanning, we cannot determine the causal relationships among aging, glymphatic dysfunction, and dopaminergic denervation, nor to clarify whether glymphatic dysfunction is one of the driving factors or merely a concomitant phenomenon of dopaminergic deficits in PD. The gene discussed is SLC6A3; the disease is Parkinson disease.