APP and hippocampal atrophy: The etiology of early-onset Alzheimer’s disease (AD) has a strong genetic component and mutations in genes that encode for amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) give rise to a rare but severe form of familial dementia characterized by cortical and hippocampal atrophy and progressive cognitive decline (Saunders, 2001; Nacmias et al., 2014; Lanoiselee et al., 2017).