APOE and Alzheimer disease: In fact, HSV1 DNA presence in normal elderly brains as well as in AD brains has been well established: data from several hundred studies, using a great variety of methods, are consistent with HSV1 presence in brain, with virus activity and state of latency or reactivation, and many are consistent with the concept that HSV1 in brain of APOE-ε4 carriers confers a high risk of AD.