Plasma neurofilament light (NfL), glial fibrillary acidic protein (GFAP), phosphorylated tau181, amyloid-β (Aβ)42, and Aβ40 were measured using ultrasensitive Simoa in early-stage patients with MSA (n = 73), spinocerebellar ataxia (SCA, n = 29), Parkinson’s disease (PD, n = 28), and healthy controls (n = 100). Here, GFAP is linked to multiple system atrophy.