Less than 5% of all AD cases are genetically based (familial AD, FAD) due to mutations in the genes encoding for APP or presenilin1 (PS1) and presenilin2 (PS2), proteins involved in the proteolytic cleavage of APP, leading to an earlier age of onset (Scheuner et al., 1996; Hardy, 1997). Here, APP is linked to familial Alzheimer disease.