Consequently, we hypothesized that it would have been worthwhile to explore some possible general demographic, cognitive and genotype-associated aspects on TBI and cognitive decline by cross-sectional analyses using existing databases that contain already a sufficient amount of information on subjects prospectively assessed for cognitive and non-cognitive domains (e.g., motor, behavior), history of TBI, TBI time points, and APOE genotype frequencies (being the allele APOE4 is a well-known genetic risk factor for AD and other dementias) (39). The gene discussed is APOE; the disease is Alzheimer disease.