This low level may correspond to PD patients affected in the same time by AD: It was reported ~ 40% of all patients with Lewy body disorders (LBD) [31] have sufficient amyloid plaque and tau tangle pathology for a concomitant Alzheimer’s disease diagnosis at autopsy and that lower Aβ1-42 levels are predictive of increasing cerebral Alzheimer’s disease and both α-synuclein pathology [32]. Here, SNCA is linked to Alzheimer disease.