These alterations in APP metabolism are due to mutations in the PSEN1 [presenilin‐1 (PS1)], PSEN2 [presenilin‐2 (PS2)], and APP genes in familial AD (FAD), or by unknown causes in sporadic cases (SAD) (Goedert & Spillantini, 2006). Here, PSEN2 is linked to familial Alzheimer disease.