Within APP/PS1 mice, a transgenic AD mouse model which have elevated production of β-amyloid, germ-free (GF) mice had a drastic reduction of cerebral β-amyloid pathology, whereas increased cerebral Aβ amyloid pathology was observed in GF mice colonized with the “diseased” microbiota of conventional mice9. The gene discussed is APP; the disease is amyloidosis.