PSEN1 and Alzheimer disease: There are two forms of AD: the familial form characterized by an early onset of symptoms, around the age of 50, due to an autosomal dominant inheritance of mutations in the genes encoding the amyloid precursor protein (APP) and presenilin 1 and 2 (PSEN1 and PSEN2) that affect the production of the amyloid beta peptide (Aβ); and the sporadic form that accounts for more than 95% of patients, and which usually develops after the age of 65 [21,25,26].