Interestingly, AD itself seems to be a significant risk factor for HSV-1 infection, as APOE ε4 carriers are frequency linked to HSV-1 reactivation, supported by its presence in IgM-positive subjects or those with elevated levels of IgG, while no significant association was found in APOE ε4-negative subjects [54]. The gene discussed is APOE; the disease is Alzheimer disease.