PD biomarkers fall into five main types: clinical (motor and non-motor symptoms), imaging (e.g., dopamine transporter scans), biochemical (e.g., α-synuclein in CSF or blood), genetic (e.g., LRRK2 and GBA mutations), and digital (data from wearables and apps) [268,269]. The gene discussed is SLC6A3; the disease is Parkinson disease.