PSEN1 and Alzheimer disease: However, prolonged exposure to Aβ in aged APP/PS1 mice drove a marked, more than 2-fold reduction in synapse density in this compartment compared to juvenile and weaned APP/PS1 mice (AD: aged 1.71 ± 0.20 vs. juvenile 4.54 ± 0.24 puncta/μm, Tukey’s multiple-comparisons corrected p = 3.1 × 10−10; aged vs. weaned 3.83 ± 0.38 puncta/μm, Tukey’s multiple-comparisons corrected p = 2.7 × 10−6; Figure S5I).