APOE and Parkinson disease: The concentration of CSF total apoE in CU Aβ− group was statistically, but not substantially, higher compared with MCI (p < 0.05, AUC = 0.54), PD (p < 0.05, AUC = 0.55), and PDD patients (p < 0.05, AUC = 0.58) (Fig. 2a).