APP and Alzheimer disease: Previous studies have found that early onset/familial AD gene mutations, such as presenilin 1/2 and amyloid precursor protein, can be detected in the carriers at very early-stage AD when cognitive abilities are still intact (Selkoe, 1997; Selkoe, 2001; Chhatwal et al., 2013; Van Cauwenberghe et al., 2016).