Although recent evidence indicates that the Aβ cascade hypothesis is debatable [27], Aβ plaques play a major role in the progression of the disease [28], while mutations in the APP gene, along with those in presenilin 1 (PSEN1) and presenilin 2 (PSEN2) genes, are linked to early-onset familial forms of AD [29,30]. The gene discussed is PSEN2; the disease is Alzheimer disease.