Mutations in three genes involved in β-amyloid protein precursor cleavage by γ- and β-secretases, namely APP, presenilin 1 (PSEN1), and presenilin 2 (PSEN2), cause early-onset familial AD (fAD) [12,13,14,15,16,17,18]. Here, PSEN2 is linked to familial Alzheimer disease.