For example, a Pennsylvania cohort identified four serum proteins—bone sialoprotein (BSP), osteomodulin (OMD), aminoacylase-1 (ACY1), and growth hormone receptor (GHR)—as PD biomarkers, yet these were not specific to PD when compared to ALS or mild cognitive impairment [41]. Here, IBSP is linked to amyotrophic lateral sclerosis.