Besides its potential impact on cognitive decline in PD, the direct influence of APOE-ε4 on α-synuclein pathology could contribute to the earlier age of PD onset in the ε4 carriers observed in our study, and reported previously.46,47 Both of these studies used time of self-reported onset of cardinal PD symptoms, and our study reaffirms this finding of a younger age at clinical PD diagnosis in APOE-ε4 carriers in a population-based cohort. This evidence concerns the gene SNCA and Parkinson disease.