In AD, the Braak hypothesis posits tau pathology begins in the transentorhinal cortex, potentially initiated by oral/nasal microbial products via the olfactory bulb, as neurofibrillary tangles are found in the olfactory epithelium (Braak and Del Tredici, 2015; Shimizu et al., 2004). This evidence concerns the gene MAPT and Alzheimer disease.