Pathogenic mutations in three genes encoding for proteins involved in the maturation and aggregation of Aβ, namely PSEN1 (presenilin-1), PSEN2 (presenilin-2) and APP (amyloid precursor protein), are causative of familial early-onset forms of AD affecting individuals under the age of 65 years with an autosomal dominant pattern of inheritance [10]. Here, APP is linked to Alzheimer disease.