It is also worth noting that in a study of 46 AD patients and 44 non-AD elderly individuals, the APOE-ε4 allele was overrepresented in AD patients positive for herpes simplex virus type 1 (HSV1) in the brain in comparison to those negative for the virus and even to non-AD patients positive for HSV1, with an OR of 16.8 (Itzhaki et al., 1997). This evidence concerns the gene APOE and Alzheimer disease.