During periodontitis, the presence of pathogens in the oral cavity leads to an increase in Aβ (which reflects in increased protein in plasma) and Tau-p, which, combined with APOE allele depletion and increased inflammation, allows molecules to migrate through a compromised blood–brain barrier to the brain, where they may contribute to cognitive impairment and the exacerbation of AD [119]. The gene discussed is APOE; the disease is Alzheimer disease.