The Tg-AD rat model expresses two human genes driven by the mouse prion promoter, APPswe (Swedish) mutation, and human presenilin-1 exon 9 deletion (PS1ΔE9)25,26 at levels that are respectively 2.6 and 6.2 higher than their endogenous rat counterparts25. The gene discussed is PSEN1; the disease is Alzheimer disease.