Furthermore, results from the Biomarkers in Parkinson’s Disease (MARK-PD) study indicated that circulating NFL levels could predict the severity and progression of cognitive decline (DRS-2 change in plasma; decrease in MoCA score > 2 points in serum) but not motor aggravation (UPDRS III ≥ 5 points in plasma; increased UPDRS III > 4 points in serum) [106,108,109]. Here, NEFL is linked to Mental deterioration.