PSEN1 and Onset: The murine Aβ peptide does not aggregate to form amyloid plaques, so the authors used the well-characterized APPPS1-21–transgenic mouse line (11) that expresses human amyloid precursor protein (APP) with the Swedish mutation (KM670/671NL) (12) and human presenilin 1 (PS1) with the L166P mutation (13), both of which cause early-onset autosomal dominant AD in humans.