Despite most AD cases being sporadic, 1% of cases represent an early-onset, familial subtype of the disease (FAD), which is caused by mutations in the amyloid precursor protein (APP) [15], presenilin 1 (PSEN1) [16], and presenilin 2 (PSEN2) [17] genes. The gene discussed is PSEN2; the disease is Alzheimer disease.