A small subset (less than 2%) of AD cases result from dominantly inherited genetic mutations in genes encoding the β-amyloid precursor protein (APP) and presenilins (PSEN1 and PSEN2, Goate et al., 1991; Levy-Lahad et al., 1995; Sherrington et al., 1995). Here, PSEN1 is linked to Alzheimer disease.