In addition, among individuals who were APOE ε4 carriers, reactivation of herpes simplex virus type 1 (HSV-1) was associated with higher risk of Alzheimer’s disease (AD), but no association was found between HSV-1 and AD among those who were APOE ε4 non-carriers [17]. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.