Mutations in the amyloid protein precursor (APP) or in the catalytic subunits of γ-secretase presenilin-1 (PSEN1) and presenilin-2 (PSEN2) are related to familial cases of AD (fAD) with an early onset of the disease, which represents the 5% of AD cases [72]. The gene discussed is PSEN2; the disease is Alzheimer disease.