The apoE isoform-dependent effects of XN on behavioral and cognitive performance and molecular measures are striking considering the role of apoE in Alzheimer’s pathology in mutants mice (Bales et al., 1997) and the enhanced ability of human apoE3 or apoE4 to delay AD pathology compared to mouse apoE (Fagan et al., 2002). The gene discussed is APOE; the disease is Alzheimer disease.