The discovery of mutations in amyloid precursor protein (APP) causing AD and the development of transgenic mouse lines overexpressing mutant APP reproducing many pathological features of AD all strongly suggest that accumulation of Aβ can cause AD, at least in its familial forms (St George-Hyslop, 2000; Bird, 2005; Gatz et al., 2006; Goedert and Spillantini, 2006; Roberson and Mucke, 2006; Haass and Selkoe, 2007). This evidence concerns the gene APP and Alzheimer disease.