Changes in three distinct genes—amyloid precursor protein (APP), amyloid beta (A4), presenilin 1 (PSEN1), and presenilin 2 (PSEN2)—have been pinpointed as the primary culprits behind early-onset Alzheimer’s disease (EOAD) [42]. The gene discussed is PSEN1; the disease is early-onset autosomal dominant Alzheimer disease.