PSEN1 and Alzheimer disease: Mutations in APP and in the Presenilin’s, PS1 and PS2 are associated with increased aggregation of the Aβ peptides in the brain’s parenchyma through an increased overall production of all Aβ species (e.g., APP duplications or APP mutations located around the β cleavage site) or production of a more aggregated form of the Aβ peptide, leading to AD [62].