Patients suffering from familial AD (fAD) develop cognitive impairment and dementia between 50 and 65 years and bear mutations in one of the three genes involved in the β-amyloidogenic pathway: APP, presenilin 1 (PSEN1), and presenilin 2 (PSEN2); increased APP dosage is also causative of AD and CAA [58–64]. This evidence concerns the gene PSEN2 and Alzheimer disease.