The Down syndrome mouse was the Tc(Hsa21)1TybEmcf (Tc1) model (O’Doherty et al., 2005), which carries a freely segregating chromosome 21 and is trisomic for 75% of the genes on this chromosome but, importantly, is not functionally triplicated for APP (Sheppard et al., 2012; Gribble et al., 2013). The gene discussed is APP; the disease is Down syndrome.