PSEN2 and Alzheimer disease: Specifically, four groups of mice were included: a control group; a group expressing human wild type presenilin-2 (PS-2), a protein that when mutated determines the onset of AD; a group expressing mutated human PS-2; and a group expressing mutated human PS-2 but subjected to treadmill exercise 50 min a day, 5 days a week, for a total of 6 weeks.