a–c, Individual α-syn aggregation curves are shown in the presence of CSF samples (40 μl) from all study participants, including healthy controls (a; n = 56), patients with MSA (b; n = 75) and patients with PD (c; n = 94). The α-syn-PMCA assay was started by adding α-syn monomers (1 mg ml−1) and ThT (5 μM) to 100 mM PIPES, pH 6.5 containing 500 mM NaCl. The plate was incubated at 37 °C with intermittent shaking for 1 min every 30 min at 500 rpm. The extent of aggregation was monitored using a fluorometer to measure ThT fluorescence, with an excitation of 435 nm and emission of 485 nm. The colours represent the expected aggregation curves for patients with PD (red), patients with MSA (blue) and healthy controls (black), regardless of clinical diagnosis.