It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this c

It's actually many, many genes that are overexpressed and result in the Down syndrome phenotype. My work is with adults with DS and Alzheimer disease--in this case, triplication of the amyloid precursor protein (APP) gene on chromosome 21 nearly guarantees accelerated development of cerebral amyloid deposition compared to typically developing people. But that's just a miniscule part of the Down syndrome phenotype.