PSEN1 and Alzheimer disease: The causes of AD are unknown, but some evidence has been gained from identifying abnormalities in selected genes, including the beta-amyloid precursor protein gene, APP, and the presenilin genes, PSEN1 and PSEN2. In addition, it has been suggested that there may be alterations of epigenetic factors due to aging or in response to environmental stresses (Wang et al., 2008; Coppieters and Dragunow, 2011; Bihaqi et al., 2012).