The presence of the amyloid precursor protein (APP) gene on Hsa21 plays a role in this early onset AD [4,9], but other genes on this chromosome (e.g., RCAN1 and Dyrk1A) might also play a role in the development of AD pathology and clinical manifestations of dementia [10,11,12]. This evidence concerns the gene DYRK1A and Alzheimer disease.