APOE and Alzheimer disease: Apolipoprotein E (APOE), having three common protein isoforms (ɛ2, ɛ3, and ɛ4), is involved in neuronal repair and plasticity [4] and carriers of the ɛ4 allele are at increased risk for neurological conditions such as Alzheimer’s disease (AD) [5] and poor outcome following moderate and severe TBI [6].