Levels of α-synuclein in the plasma correlate with cognitive impairment — but not motor symptom severity — in patients with Parkinson disease (PD), research from Taiwan indicates. Ming-Jang Chiu and co-workers used an ultrasensitive immunoassay to measure plasma levels of α-synuclein in 80 patients with PD and 34 controls. Overall, the levels were higher in the patients with PD than in the controls, and were further elevated in PD patients with cognitive impairment. By contrast, no significant correlation was found between plasma α-synuclein levels and motor symptom severity in the PD group. The findings raise the possibility that plasma α-synuclein could serve as a biomarker to gauge the risk of cognitive decline in patients with PD.