Extracellular amyloid beta (Aβ) plaques are a hallmark of AD, composed of fragments of amyloid precursor protein (APP) [79, 80] generated by presenilin secretases (PSEN1/2) [81], with APP [82, 83] and PSEN genes [84, 85] mutated in familial AD. Here, PSEN1 is linked to Alzheimer disease.