PCSK9 and Parkinson disease: This study aimed to identify serum biomarkers associated with PD-CI and investigate the synergistic contributions of lipid metabolism and inflammatory signaling.<h4>Methods</h4>In this retrospective, cross-sectional study, six candidate proteins (INPP5D, FLNA, ICAM-1, PCSK9, JAK1, and LCAT) were selected based on our previously published discovery-phase serum proteomics analysis and were quantified via ELISA in an independent cohort of 75 PD patients and 35 age-matched healthy controls (HCs).