A diminished level of salivary lactoferrin, a credible biomarker for Aβ accumulation in AD brains, has been found more recently, because a lower level of salivary lactoferrin altered the oral microbiota, which was an outcome of poor oral hygiene and dry mouth in the elderly and promoted oral bacteria to grow and to spread elsewhere in the body (Nie et al., 2019). This evidence concerns the gene LTF and Alzheimer disease.