We found four top biomarker candidates—ACY1, BSP, GHR, and OMD—that replicated across a single-site Discovery Cohort and a multisite Replication Cohort, were robust to common sources of preanalytical variability, and did not differ in paired samples from PD participants on versus off dopaminergic medication. This evidence concerns the gene ACY1 and occult macular dystrophy.