While the link between the microbiome and brain disorders is starting to emerge18, 19, 20 the impact of gastro-intestinal microbes on the development of AD is not known and has also not adequately been addressed in model system despite often anecdotal evidence that amyloid plaque formation in APP transgenic mice differs among mouse facilities with different specific-pathogen-free (SPF) conditions21, 22. The gene discussed is APP; the disease is Alzheimer disease.