DS may therefore be viewed as a genetic cause of AD alongside known autosomal dominant pathogenic mutations in the APP, presenilin-1 (PSEN1), and presenilin-2 (PSEN2) genes (autosomal dominant AD [ADAD]) [5], although the clinical course during the early stages of AD in DS is less well described [6]. This evidence concerns the gene PSEN1 and Alzheimer disease.