PSEN1 and familial Alzheimer disease: Mutations in the PSEN1 gene, located on chromosome 14, encodes the presenilin-1 (PS1) protein, and have been found to be the main causative mutations in FAD with PSEN1 considered the most common AD-related gene in this disorder (Kelleher and Shen 2017; Lanoiselee et al. 2017).