Acceleration of scrapie in trisomy 16----diploid aggregation chimeras. We studied the susceptibility to prion infection of the trisomy 16----diploid chimeric mouse, a putative model of Down syndrome. When weanling chimeras were inoculated intracerebrally with scrapie prions, the time until appearance of the first symptoms of scrapie was reduced by 17 days (from a mean control time of 153 days) and the time to death was reduced by 30 days (from control time of 170 days). Our results with trisomy 16 chimeras argue that the susceptibility to central nervous system degeneration caused by prions can be modulated by chromosome imbalance. 