PSEN1 and Alzheimer disease: In a small percentage of cases, however, patients that carry specific mutations in the amyloid precursor protein (APP), presinilin-1 (PSEN1), or presinilin-2 (PSEN2) genes will develop an autosomal dominant form of AD known as familial AD (FAD) (Campion et al., 1999; Bateman et al., 2012; Cruchaga et al., 2012; Long and Holtzman, 2019).