by Leah E. Escalante, James Hose, Jamie M. Ahrens, Hollis Howe, Norah Paulsen, Sofia J. Liss, Michael Place, Audrey P. Gasch Down syndrome, caused by an extra copy of Chromosome 21, causes lifelong problems. One of the most common phenotypes among people with Down syndrome is premature aging, including early tissue decline, neurodegeneration, and shortened life span. Yet the reasons for premature systemic aging are a mystery and difficult to study in humans. Here we show that chromosome amplifi