Posavi M, Diaz-Ortiz M, Liu B, et al. - Researchers provided a molecular characterization of individuals with Parkinson disease (PD) via assessing blood-based biomarkers for diagnostic confirmation and prediction of progression. Using an aptamer-based platform, they measured levels of 1,129 proteins in 141 plasma samples (96 PD, 45 neurologically normal control [NC]; 45.4% female; mean age: 70.0 years) from a longitudinally followed Discovery Cohort based at the University of Pennsylvania. They ranked these candidate proteins via Stability Selection. In a replication cohort of 317 individuals (215 PD, 102 NC; 47.9% female; mean age: 66.7 years) from the multisite, longitudinally followed National Institute of Neurological Disorders and Stroke Parkinson Disease Biomarker Program Cohort, they performed confirmation of the findings from the discovery cohort. Findings revealed that people with PD consistently differed from people without PD in terms of blood levels of four proteins—bone sialoprotein, osteomodulin, aminoacylase-1, and growth hormone receptor (GHR). Lower GHR levels at baseline were identified to be predictive of a faster rate of cognitive decline in people with PD.