Adults with DS are the largest population with an increased risk for Alzheimer's disease (AD) associated with a specific genotype, as an extra copy of the gene coding for amyloid precursor protein (APP) located on chromosome 21 leads to its overproduction and consequent atypical deposition of amyloid beta (Aβ).5, 6. Here, APP is linked to early-onset autosomal dominant Alzheimer disease.