APOE and Alzheimer disease: The apolipoprotein E (APOE) gene is now recognized as the most influential genetic factor in sporadic late-onset Alzheimer’s disease (LOAD) [1,2,3], but emerging evidence suggests APOE plays a role in other neurological conditions, including PD, Parkinson’s related dementia (PDD), and acquired brain injury, defining different clinical subtypes [4,5].