Lower Plasma α-Synuclein Levels are Associated with Cognitive Impairment in Parkinson's Disease

Background: alpha-Synuclein (alpha-syn) has a central role in the development of Parkinson's disease (PD). Plasma alpha-syn has been associated with the presence of cognitive impairment in PD although data have been inconsistent. The aim of this study was to explore the correlation between plasma alpha-syn levels and cognitive impairment in PD. Methods: A total of 53 participants, 26 patients with PD and 27 healthy controls were included in the study. Unified Parkinson's Disease Rating Scale (UPDRS) part. and Hohen-Yahr scale (H-Y scale) were used to detect PD severity. The cognitive function was assessed with Montreal Cognitive Assessment (MoCA) scale, Frontal Assessment Battery (FAB), Trail Making Test A (TMT-A), Verbal Function Test (VFT), Clock Drawing Test (CDT), and Rey's Auditory Verbal Learning Test (RAVLT). Enzyme-Linked Immunosorbent Assay (ELISA) method was used to measure alpha-syn and hemoglobin (Hb) concentration in the plasma samples collected from participants. Results: Plasma alpha-syn in PD patients was significantly lower than those in the control group (p < 0.01). No associations were found between plasma alpha-syn and Hb or gender (p > 0.05). The decline in plasma alpha-syn in PD patients was negatively correlated with disease severity, including UPDRS. scores and H-Y scale. Furthermore, lower plasma alpha-syn was negatively associated with the scores of MoCA, FAB, and RAVLT (immediate recall) scores in PD group. Conclusions: Our data suggest that lower plasma alpha-syn levels are associated with cognitive decline in PD. Thus, plasma alpha-syn may be a novel biomarker for patients at risk of cognitive decline.