Recent animal model work has shown that the ɛ4 allele is independently associated with α-synuclcin pathology and toxicity.29 In addition, the ɛ4 allele is overrepresented in dementia with Lewy body cases with “pure” Lewy body pathology, compared with PDD cases.30 A systematic review showed that limbic and neocortical α-synuclcin pathology had the strongest association with PD dementia.28 Further work is needed to determine the mechanisms by which APOE influences cognitive decline. Here, APOE is linked to dementia.