Although the main cause of AD in Down syndrome individuals is likely to be the additional copy of the APP gene encoded by chromosome 21 (reviewed in Kingsbury et al., 2006), mice overexpressing APP (which encodes amyloid beta A4 protein) do not fully recapitulate all the AD-like phenotypes seen in Down syndrome mouse models (Cataldo et al., 2003). The gene discussed is APP; the disease is Down syndrome.