Alzheimer presenilins in the nuclear membrane, interphase kinetochores, and centrosomes suggest a role in chromosome segregation.

Mutations in two related genes, presenilin 1 and 2, account for most early-onset familial Alzheimer's disease. Although structural features indicate that the presenilins are membrane proteins, their function(s) is unknown. We have localized the presenilins to the nuclear membrane, its associated interphase kinetochores, and the centrosomes-all subcellular structures involved in cell cycle regulation and mitosis. The colocalization of the presenilins with kinetochores on the nucleoplasmic surface of the inner nuclear membrane, together with other results, suggests that they may play a role in chromosome organization and segregation, perhaps as kinetochore binding proteins/receptors. We discuss a pathogenic pathway for familial Alzheimer's disease in which defective presenilin function causes chromosome missegregation during mitosis, resulting in apoptosis and/or trisomy 21 mosaicism.