APOE and Alzheimer disease: Consistent with the notion that the AD phenotype may be oligogenic and characterized by select, penetrant genes, APOE ε4 carrier status was a strong predictor of CSF Aβ42/40, which is consistent with prior research showing APOE ε4 is the greatest genetic risk locus for AD.16APOE ε4 carrier status did not interact with TBI, which further supports the hypothesis that TBI may implicate more peripheral genetic pathways of AD.