Mutations identified in familial forms of AD (FAD) indicate a causal role for the amyloid precursor protein (APP) and presenilin (PSEN1/PSEN2) genes, which encode the precursor of Aβ and the ɣ-secretase enzyme that catalyses the final step of Aβ peptide production, respectively2,3. This evidence concerns the gene APP and Alzheimer disease.