SAA: seed amplification assays; CSF: cerebrospinal fluid; PD: Parkinson’s disease; DAT-SPECT: dopamine transporter single-photon emission CT; α-syn PET: α-synuclein positron-emission tomography; NfL: neurofilament light; GFAP: glial fibrillary acidic protein; GBA: glucocerebrosidase; LRRK2: leucine-rich repeat kinase 2; PRS: polygenic risk score. The gene discussed is GBA1; the disease is Parkinson disease.