Apoptotic proteolytic cleavage of the presenilins by caspases.

Familial Alzheimer's disease (FAD) is a genetically heterogeneous disorder that is caused by defects in at least three early onset genes (age of onset:<60 yr.): presenilin 2 (PS2) on chromosome 1 (1), presenilin 1 (PS1) on chromosome 14 (2), and amyloid protein precursor (APP) on chromosome 21 (3,4). Mutations within the APP gene are responsible for only a small portion (<2%) of reported cases of FAD (5), whereas up to half of all early onset FAD cases are caused by mutations in the PSEN1 and PSEN2 genes (6,7).