MAPT and Alzheimer disease: In a study of an oral microbe, Porphyromonas gingivalis, which is the primary bacterial cause of periodontitis, Dominy et al. [195] found P. gingivalis and its toxic protease, gingipains, in the brains of AD patients by conducting tissue microarrays on AD and sex- and age-matched brain tissue cores, which correlated with tau and ubiquitin pathology.