Less than 5% of AD patients manifest symptoms at an earlier stage (before the age of 65), i.e., familial AD (FAD), which is linked to genetic mutations in one of three genes, including, amyloid precursor protein (APP), presenilin1 (PSEN1) and presenilin 2 (PSEN2) [11]. The gene discussed is PSEN2; the disease is familial Alzheimer disease.