Given the fact that APOE4 is associated with the risk of DLB and PDD, but not necessarily PD [6, 27], it is tempting to speculate that effects of APOE4 may manifest more in neocortex where AD and LBD pathologies are found, whereas it has minimal impact on subcortical or brainstem structures where Lewy pathology is predominant in PD. The gene discussed is APOE; the disease is Parkinson disease.