APP and Alzheimer disease: Moreover, the study found strong associations between alterations in the gut microbiome and changes in fecal, serum, and cortical metabolomes observed in AD mice.16 Additionally, the introduction of gut microbiota from conventionally raised mutant amyloid precursor protein (APP)/presenilin 1 (APP/PS1) transgenic mice into germ-free mutant APP/PS1 transgenic mice resulted in a significant escalation of cerebral Aβ pathology in comparison to WT mice and germ-free transgenic mice.17