PSEN1 and Alzheimer disease: Amyloid Precursor Protein (APP), Presenilin-1 (PSEN1), and Presenilin-2 (PSEN2) mutations have been identified as causative, while Apolipoprotein E (APOE) haplotype 4 (APOE4) increases the risk of developing AD 3- to fourfold [1].