The main objective of the cross-sectional study of Samat et al., [60] was to investigate the prevalence of PD-MCI among 46 PD patients using the PDCRS and MoCA test, the Level I MDS criteria [6], and to correlate the presence of cognitive dysfunction with measurable biomarkers such as ApoE4 and plasma a-synuclein. Here, APOE is linked to Parkinson disease.