PSEN1 and early-onset autosomal dominant Alzheimer disease: The group of Harach generated germ-free mice using APPPS1 mice as an animal model of Alzheimer's disease (a double transgenic mice expressing mutated forms of the genes for human amyloid protein (APP) and presenilin 1) and found a drastic reduction of cerebral amyloid pathology when compared with control APP mice with intestinal microbiota.