Particularly, three EOAD genes—amyloid precursor protein (APP) [19], presenilins 1 and 2 (PSEN1 [20] and PSEN2 [21,22])—show high-penetrant mutations inherited as autosomal dominant trait [23,24,25] (i.e., autosomal dominant AD [ADAD] forms representing <1% of all AD cases) [26,27]. This evidence concerns the gene PSEN1 and Alzheimer disease.