SLC6A3 and multiple system atrophy: <h4>Objective</h4>The objective of this study was to characterize changes in candidate biomarkers in early multiple system atrophy (MSA) and identify baseline predictors of faster progression.<h4>Methods</h4>This 1-year, multicenter, prospective study assessed clinical, neuroimaging (3T-magnetic resonance imaging [MRI], dopamine transporter single-photon emission computed tomography [DaT-SPECT]), and neurofilament light chain (NfL) changes in patients with early MSA (< 5 years from symptom onset) and healthy controls (HCs).