It has been shown that the APOE-epsilon 4 allele frequency was significantly higher in patients positive for HSV-1 in the brain than in the HSV-1-negative AD group, the HSV-1-positive non-AD group, or the HSV-1-negative non-AD group (52.8% vs. 10.0%, 3.6%, and 6.3%, respectively), supporting that AD patients are more susceptible to HSV-1 [107]. The gene discussed is APOE; the disease is Alzheimer disease.