PSEN2 and Alzheimer disease: Early-onset AD is related to mutations in the three familial AD genes, namely amyloid precursor protein (APP, multiple mutations such as 670/671 Swedish mutation for favoring β-secretase cleavage, 717 transmembrane domain mutation for overproduction of Aβ42, A692G Flemish/E693Q Dutch, and p. E693G Arctic mutations for facilitating Aβ protofibril formation) on chromosome 21q21.3, presenilin 1 (PSEN1, S182) on chromosome 14q24.3, and presenilin 2 (PSEN2) on chromosome lq42.13 (Sisodia and St George-Hyslop, 2002; Tsatsanis et al., 2020).