Using a mouse model of early-onset Alzheimer’s disease, the amyloid precursor protein/presenilin 1 (APP/PS1) transgenic model transfer of the microbiota from conventional-raised mice to germ-free mice resulted in increased cerebral pathology, providing evidence that microbiota plays a key role in the development of neurodegenerative diseases [37]. This evidence concerns the gene PSEN1 and neurodegenerative disease.