PSEN1 and early-onset autosomal dominant Alzheimer disease: Variants in three genes, the Amyloid Precursor Protein (APP), Presenilin 1 (PSEN1) and Presenilin 2 (PSEN2), cause early onset familial AD (EOFAD; < 60 years of age), which overlap clinically and pathologically with late-onset sporadic presentations of AD (LOAD; > 60 years of age) [4, 5].